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Authors: Connor Tansley, Nicola J. Patron, and Sarah Guiziou
ACS Synthetic Biology (2024)
Abstract: "Many plant species are grown to enable access to specific organs or tissues, such as seeds, fruits, or stems. In some cases, a value is associated with a molecule that accumulates in a single type of cell. Domestication and subsequent breeding have often increased the yields of these target products by increasing the size, number, and quality of harvested organs and tissues but also via changes to overall plant growth architecture to suit large-scale cultivation. Many of the mutations that underlie these changes have been identified in key regulators of cellular identity and function. As key determinants of yield, these regulators are key targets for synthetic biology approaches to engineer new forms and functions. However, our understanding of many plant developmental programs and cell-type specific functions is still incomplete. In this Perspective, we discuss how advances in cellular genomics together with synthetic biology tools such as biosensors and DNA-recording devices are advancing our understanding of cell-specific programs and cell fates. We then discuss advances and emerging opportunities for cell-type-specific engineering to optimize plant morphology, responses to the environment, and the production of valuable compounds."
Authors: Haiqiang Zhang, Zichen Liu, Yunxiao Wang, Siyu Mu, Hongzhong Yue, Yanjie Luo, Zhengao Zhang, Yuhong Li and Peng Chen.
Theoretical and Applied Genetics (2024)
Key message A novel super compact mutant, scp-3, was identified using map-based cloning in cucumber. The CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase was the candidate gene of scp-3.
Abstract: "Mining dwarf genes is important in understanding stem growth in crops. However, only a small number of dwarf genes have been cloned or characterized. Here, we characterized a cucumber (Cucumis sativus L.) dwarf mutant, super compact 3 (scp-3), which displays shortened internodes and dark green leaves with a wrinkled appearance. The photosynthetic rate of scp-3 is significantly lower than that of the wild type. The dwarf phenotype of scp-3 mutant can be partially rescued by the exogenous brassinolide (BL) application, and the endogenous brassinosteroids (BRs) levels in the scp-3 mutant were significantly lower compared to the wild type. Microscopic examination revealed that the reduced internode length in scp-3 resulted from a decrease in cell size. Genetic analysis showed that the dwarf phenotype of scp-3 was controlled by a single recessive gene. Combined with bulked segregant analysis and map-based cloning strategy, we delimited scp-3 locus into an 82.5 kb region harboring five putative genes, but only one non-synonymous mutation (A to T) was discovered between the mutant and its wild type in this region. This mutation occurred within the second exon of the CsGy4G017510 gene, leading to an amino acid alteration from Leu156 to His156. This gene encodes the CsDWF7 protein, an analog of the Arabidopsis DWF7 protein, which is known to be involved in the biosynthesis of BRs. The CsDWF7 protein was targeted to the cell membrane. In comparison to the wild type, scp-3 exhibited reduced CsDWF7 expression in different tissues. These findings imply that CsDWF7 is essential for both BR biosynthesis as well as growth and development of cucumber plants."
Authors: Gökhan Boyno, Younes Rezaee Danesh, Semra Demir, Necmettin Teniz, José M. Mulet and Rosa Porcel.
International Journal of Molecular Sciences (2023)
Abstract: "Plants, the cornerstone of life on Earth, are constantly struggling with a number of challenges arising from both biotic and abiotic stressors. To overcome these adverse factors, plants have evolved complex defense mechanisms involving both a number of cell signaling pathways and a complex network of interactions with microorganisms. Among these interactions, the relationship between symbiotic arbuscular mycorrhizal fungi (AMF) and strigolactones (SLs) stands as an important interplay that has a significant impact on increased resistance to environmental stresses and improved nutrient uptake and the subsequent enhanced plant growth. AMF establishes mutualistic partnerships with plants by colonizing root systems, and offers a range of benefits, such as increased nutrient absorption, improved water uptake and increased resistance to both biotic and abiotic stresses. SLs play a fundamental role in shaping root architecture, promoting the growth of lateral roots and regulating plant defense responses. AMF can promote the production and release of SLs by plants, which in turn promote symbiotic interactions due to their role as signaling molecules with the ability to attract beneficial microbes. The complete knowledge of this synergy has the potential to develop applications to optimize agricultural practices, improve nutrient use efficiency and ultimately increase crop yields. This review explores the roles played by AMF and SLs in plant development and stress tolerance, highlighting their individual contributions and the synergistic nature of their interaction."
Authors: Chang Su, Andrzej Kokosza, Xiaonan Xie, Aleš Pěnčík, Youjun Zhang, Pasi Raumonen, Xueping Shi, Sampo Muranen, Melis Kucukoglu Topcu, Juha Immanen, Risto Hagqvist, Omid Safronov, Juan Alonso-Serra, Gugan Eswaran, Mirko Pavicic Venegas, Karin Ljung, Sally Ward, Ari Pekka Mähönen, Kristiina Himanen, Jarkko Salojärvi, Alisdair R. Fernie, Ondřej Novák, Ottoline Leyser, Wojtek Pałubicki, Ykä Helariutta and Kaisa Nieminen.
PNAS (2023)
Significance What makes a tree a tree instead of a bush? Through a candidate gene approach, we identified a natural bush-like (short and highly branching) SL-deficient birch mutant, kanttarelli, with an early STOP codon in an essential SL biosynthesis gene, BpMAX1. The number of higher-order branches was increased in the mutant and in phenocopying transgenic RNAi -lines. Intriguingly, the auxin concentration formed a gradient along the main stem in the WT, with more auxin in the uppermost internodes and less toward the base, whereas in the transgenic line this gradient was absent. Mathematical modeling showed that this difference in auxin distribution may result from the differing architectures. Our results could be applied in the breeding of trees with an optimized architecture.
Abstract: "Due to their long lifespan, trees and bushes develop higher order of branches in a perennial manner. In contrast to a tall tree, with a clearly defined main stem and branching order, a bush is shorter and has a less apparent main stem and branching pattern. To address the developmental basis of these two forms, we studied several naturally occurring architectural variants in silver birch (Betula pendula). Using a candidate gene approach, we identified a bushy kanttarelli variant with a loss-of-function mutation in the BpMAX1 gene required for strigolactone (SL) biosynthesis. While kanttarelli is shorter than the wild type (WT), it has the same number of primary branches, whereas the number of secondary branches is increased, contributing to its bush-like phenotype. To confirm that the identified mutation was responsible for the phenotype, we phenocopied kanttarelli in transgenic BpMAX1::RNAi birch lines. SL profiling confirmed that both kanttarelli and the transgenic lines produced very limited amounts of SL. Interestingly, the auxin (IAA) distribution along the main stem differed between WT and BpMAX1::RNAi. In the WT, the auxin concentration formed a gradient, being higher in the uppermost internodes and decreasing toward the basal part of the stem, whereas in the transgenic line, this gradient was not observed. Through modeling, we showed that the different IAA distribution patterns may result from the difference in the number of higher-order branches and plant height. Future studies will determine whether the IAA gradient itself regulates aspects of plant architecture."
Authors: Shuping Jiao, Sujan Mamidi, Mark A. Chamberlin, Mary Beatty, Shawn Thatcher, Kevin D. Simcox, Fanna Maina, Hu Wang-Nan, Gurmukh S. Johal, Lynn Heetland, Sandeep R. Marla, Robert B. Meeley, Jeremy Schmutz, Geoffrey P. Morris and Dilbag S. Multani.
New Phytologist (2023)
Abstract: "In the current genomic era, the search and deployment of new semi-dwarf alleles have continued to develop better plant types in all cereals. We characterized an agronomically optimal semi-dwarf mutation in Zea mays L. and a parallel polymorphism in Sorghum bicolor L. We cloned the maize brachytic1 (br1-Mu) allele by a modified PCR-based Sequence Amplified Insertion Flanking Fragment (SAIFF) approach. Histology and RNA-Seq elucidated the mechanism of semi-dwarfism. GWAS linked a sorghum plant height QTL with the Br1 homolog by resequencing a West African sorghum landraces panel. The semi-dwarf br1-Mu allele encodes an MYB transcription factor78 that positively regulates stalk cell elongation by interacting with the polar auxin pathway. Semi-dwarfism is due to differential splicing and low functional Br1 wild-type transcript expression. The sorghum ortholog, SbBr1, co-segregates with the major plant height QTL qHT7.1 and is alternatively spliced. The high frequency of the Sbbr1 allele in African landraces suggests that African smallholder farmers used the semi-dwarf allele to improve plant height in sorghum long before efforts to introduce Green Revolution-style varieties in the 1960s. Surprisingly, variants for differential splicing of Brachytic1 were found in both commercial maize and smallholder sorghum, suggesting parallel tuning of plant architecture across these systems."
Authors: Lin Du, Jijun Yan, Chunxin Yu, Chunying Wang, Weiming Tan and Liusheng Duan.
Journal of Plant Growth Regulation (2024)
Abstract: "Strigolactone (SL) biosynthesis inhibitors have shown impressive activity in increasing shoot branching and inhibiting seed germination of the root parasitic plants Striga spp. and Orobanche spp. Herein, novel 1H-1,2,4-triazole derivatives were designed as SL biosynthesis inhibitors based on the backbone modification strategy, 33 target compounds were chemical synthesized and screened on Arabidopsis thaliana and Oryza sativa. The structure–activity relationship analysis enabled the discovery of a potential SL biosynthesis inhibitor B4 with the promising activity in increasing shoot branching, elongating taproot by inhibiting the biosynthesis of 4-deoxyorobanchol (4DO). We further found that B4-treated A. thaliana showed increased branching phenotype with the upregulated gene expression of AtMAX3 and AtMAX4. These results indicated that B4 might be a potent SL biosynthesis inhibitor and provide a unique scaffold for the development of new SL biosynthesis inhibitors."
Authors: Keisuke Okamoto, Taiki Inoue, Tsunesato Nagano, Sho Miyazaki, Ikuo Takahashi, Tadao Asami, Kazunori Okada, Kazuma Okada and Masatoshi Nakajima.
Bioscience, Biotechnology, and Biochemistry (2023)
Abstract: "MdDOX-Co, the ectopic expression of which is considered to cause the columnar tree shape, belongs to the 2-oxoglutarate-dependent dioxygenase (2ODD) family. It adds a hydroxyl group to position 12 of gibberellins. However, the 2ODD enzymes related to gibberellin biosynthesis and catabolism are phylogenetically distinct from MdDOX-Co. Thus, it is possible that substrates other than gibberellins exist in MdDOX-Co. To identify the previously unidentified substrate(s) of MdDOX-Co, we searched for MdDOX-Co-specific inhibitors. Chemical screening using GC-MS was performed to investigate the effects of 2,400 compounds that inhibited the catalytic reaction of MdDOX-Co, but not the catabolic reaction of GA 2-oxidase, an enzyme involved in gibberellin catabolism. By applying these two compounds in Arabidopsis, a chemical designated as TPDD that did not inhibit gibberellin biosynthesis was selected. The structure-activity relationships among the TPDD analogs were also obtained."
Authors: Ting Zou, Kaixuan Zhang, Jing Zhang, Sijing Liu, Jing Liang, Jiaxu Liu, Jun Zhu, Yueyang Liang, Shiquan Wang, Qiming Deng, Huainian Liu, Jinghua Jin, Ping Li and Shuangcheng Li.
The Plant Journal (2023)
Significance Statement: The rice GRAS transcriptional factor DLT2 interacts with two brassinosteroid signaling components, DLT and OsBZR1, to regulate BR responses and plant development.
Abstract: "Brassinosteroids (BRs) are a class of steroid phytohormones that control various aspects of plant growth and development. Several transcriptional factors (TFs) have been suggested to play roles in BR signaling. However, their possible relationship remains largely unknown. Here, we identified a rice mutant dwarf and low-tillering 2 (dlt2) with altered plant architecture, increased grain width, and reduced BR sensitivity. DLT2 encodes a GIBBERELLIN INSENSITIVE (GAI)-REPRESSOR OF GAI (RGA)-SCARECROW (GRAS) TF that is mainly localized in the nucleus and has weak transcriptional activity. Our further genetic and biochemical analyses indicate that DLT2 interacts with two BR-signaling-related TFs, DLT and BRASSINAZOLE-RESISTANT 1, and probably modulates their transcriptional activity. These findings imply that DLT2 is implicated in a potentially transcriptional complex that mediates BR signaling and rice development and suggests that DLT2 could be a potential target for improving rice architecture and grain morphology. This work also sheds light on the role of rice GRAS members in regulating numerous developmental processes."
Authors: Carlos Hernán Barrera-Rojas, Mateus Henrique Vicente, Diego Armando Pinheiro Brito, Eder M. Silva, Aitor Muñoz Lopez, Leticia F. Ferigolo, Rafael Monteiro do Carmo, Carolina M. S. Silva, Geraldo F. F. Silva, Joao P. O. Correa, Marcela M. Notini, Luciano Freschi, Pilar Cubas and Fabio T. S. Nogueira.
Journal of Experimental Botany (2023)
Abstract: "The miRNA156 (miR156)/SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL/SBP) regulatory hub is highly conserved among phylogenetically distinct species, but how it interconnects multiple pathways to converge to common integrators controlling shoot architecture is still unclear. Here, we demonstrated that the miR156/SlSBP15 node modulates tomato shoot branching by connecting multiple phytohormones with classical genetic pathways regulating both axillary bud development and outgrowth. miR156-overexpressing plants (156-OE) displayed high shoot branching, whereas plants overexpressing a miR156-resistant SlSBP15 allele (rSBP15) showed arrested shoot branching. Importantly, the rSBP15 allele was able to partially restore the wild-type shoot branching phenotype in the 156-OE background. rSBP15 plants have tiny axillary buds, and their activation is dependent on shoot apex-derived auxin transport inhibition. Hormonal measurements revealed that indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations were lower in 156-OE and higher in rSBP15 axillary buds, respectively. Genetic and molecular data indicated that SlSBP15 regulates axillary bud development and outgrowth by inhibiting auxin transport and GOBLET (GOB) activity, and by interacting with tomato BRANCHED1b (SlBRC1b) to control ABA levels within axillary buds. Collectively, our data provide a new mechanism by which the miR156/SPL/SBP hub regulates shoot branching, and suggest that modulating SlSBP15 activity might have potential applications in shaping tomato shoot architecture."
Authors: Shouzhen Teng, Qiming Liu, Guoxin Chen, Yuan Chang, Xuean Cui, Jinxia Wu, Pengfei Ai, Xuehui Sun, Zhiguo Zhang and Tiegang Lu.
New Phytologist (2023)
Abstract: "Modifications of plant architecture can increase planting density, regulate photosynthesis, and improve crop yields. Many basic helix–loop–helix (bHLH) transcription factors participate in the brassinosteroid (BR) signaling pathway and are critical for plant architecture morphogenesis in rice. However, the number of identified bHLH genes suitable for improving production value is still limited. In this study, we cloned Lam1, encoding the typical bHLH transcription factor OsbHLH92. OsbHLH92 knockout (KO) lines exhibit erect leaves. Decreases in the number and size of parenchyma cell layers on the adaxial side of the lamina joint in KO lines were the main reason for the decreased leaf angle. Genetic experiments verify that OsBU1 and its homologs are downstream of OsbHLH92, which is involved in the noncanonical RGA1-mediated BR signaling pathway. OsbHLH91, an OsbHLH92 homolog, plays both conserved and differentiated roles relative to OsbHLH92. Notably, OsbHLH92-KO lines show erect leaves without the acquisition of adverse agronomic traits. Moreover, by driving a specific panicle promoter, OsbHLH92 can greatly increase productivity by at least 10%. This study identifies new components of the BR signaling pathway, demonstrates the importance of OsbHLH92 in improving planting density and crop productivity, and broadens our knowledge of typical and atypical bHLH family members in rice."
Authors: Dengan Xu, Yingjie Bian, Xumei Luo, Chenfei Jia, Qianlin Hao, Xiuling Tian, Qiang Cao, Wei Chen, Wujun Ma, Zhongfu Ni, Xiangdong Fu, Zhonghu He, Xianchun Xia and Shuanghe Cao.
Development (2023)
Summary: Transgenic, micromorphological, dynamic and multi-omic analyses in wheat reveal the underlying mechanism of the Green Revolution gene Rht-B1b in modulation of plant architecture and yield component traits.
Abstract: "The utilization of reduced plant height genes Rht-B1b and Rht-D1b, encoding homeologous DELLA proteins, led to the wheat Green Revolution (GR). However, the specific functions of GR genes in yield determination and the underlying regulatory mechanisms remained unknown. Here, we validated that Rht-B1b, as a representative of GR genes, affects plant architecture and yield component traits. Upregulation of Rht-B1b reduced plant height, leaf size and grain weight, but increased tiller number, tiller angle, spike number per unit area, and grain number per spike. Dynamic investigations showed that Rht-B1b increased spike number by improving tillering initiation rather than outgrowth, and enhanced grain number by promoting floret fertility. Rht-B1b reduced plant height by reducing cell size in the internodes, and reduced grain size or weight by decreasing cell number in the pericarp. Transcriptome analyses uncovered that Rht-B1b regulates many homologs of previously reported key genes for given traits and several putative integrators for different traits. These findings specify the pleiotropic functions of Rht-B1b in improving yield and provide new insights into the regulatory mechanisms underlying plant morphogenesis and yield formation."
Authors: Shangyu Chen, Xuewei Song, Qixiang Zheng, Yuqi Liu, Jingquan Yu, Yanhong Zhou and Xiaojian Xia.
Journal of Experimental Botany (2023)
Abstract: "Plant architecture imposes a large impact on crop yield. IDEAL PLANT ARCHITECTURE 1 (IPA1), which encodes a SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factor, is a target of molecular design for improving grain yield. However, the roles of SPL transcription factors in regulating tomato (Solanum lycopersicum) plant architecture are unclear. Here, we show that the expression of SPL13 is downregulated in the lateral buds of strigolactones (SLs)-deficient ccd mutants and is induced by GR24 (a synthetic analogue of SL). Knockout of SPL13 by CRISPR/Cas9 resulted in higher levels of cytokinins (CKs) and transcripts of CK synthesis gene ISOPENTENYL TRANSFERASES 1 (IPT1) in the stem nodes and more growth of lateral buds. GR24 suppresses CKs synthesis and lateral bud growth in ccd mutants but is not effective in spl13 mutants. Meanwhile, silencing of IPT1 gene inhibited bud growth of spl13 mutants. Interestingly, SLs levels in root extracts and exudates are significantly increased in spl13 mutants. Molecular studies indicated that SPL13 directly represses the transcription of IPT1 and the SL synthesis genes CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7) and MORE AXILLARY GROWTH 1 (MAX1). The results demonstrate that SPL13 acts downstream of SL to suppress lateral bud growth by inhibiting CKs synthesis in tomato. Tuning the expression of SPL13 is a potential approach for decreasing the number of lateral shoots in tomato."
Authors: Craig L. Cowling, Linkan Dash and Dior R. Kelley.
Journal of Experimental Botany (2023)
Abstract: "Phytohormones play a central role in plant development and environmental responses. Auxin is a classical hormone that is required for organ formation, tissue patterning, and defense responses. Auxin pathways have been extensively studied across numerous land plant lineages, including bryophytes and eudicots. In contrast, our understanding of the roles of auxin in maize morphogenesis and immune responses are limited. Here, we will review evidence for auxin-mediated processes in maize and describe promising areas for future research in the auxin field. Several recent transcriptomic and genetic studies have demonstrated that auxin is a key influencer of both vegetative and reproductive development in maize (namely roots, leaves and kernels). Auxin signaling has been implicated in both maize shoot architecture and immune responses through genetic and molecular analyses of the conserved co-repressor RAMOSA ENHANCER LOCUS2. Polar auxin transport is linked to maize drought responses, root growth, shoot formation, and leaf morphogenesis. Notably, maize has been a key system for delineating auxin biosynthetic pathways and offers many opportunities for future investigations on auxin metabolism. In addition, crosstalk between auxin and other phytohormones has been uncovered through gene expression studies and are important for leaf and root development in maize. Collectively these studies point to auxin as a cornerstone for maize biology that could be leveraged for improved crop resilience and yield."
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Authors: Jian You Wang, Guan-Ting Erica Chen, Justine Braguy and Salim Al-Babili.
Trends in Plant Science (2024)
Highlights: Strigolactones (SLs) are structurally diverse and divided into canonical and non-canonical subgroups. SLs are generally considered as plant hormones, best known for inhibiting shoot branching/tillering. SLs are rhizospheric signals important for arbuscular mycorrhizal symbiosis, which may be their ancestral function that is conserved from liverworts to flowering plants. Recent results have revealed functional specificity, indicating that canonical SLs are not the tillering/branching inhibitory hormone in rice or tomato. Increasing the content of 4-deoxyorobanchol in rice by interrupting its hydroxylation affects root, shoot, and panicle growth, suggesting that this canonical SL has hormonal functions. Reducing the levels of canonical SLs by genome editing or applying specific inhibitors is a promising strategy for reducing Striga parasitism.
Abstract: "Strigolactones (SLs) act as regulators of plant architecture as well as signals in rhizospheric communications. Reduced availability of minerals, particularly phosphorus, leads to an increase in the formation and release of SLs that enable adaptation of root and shoot architecture to nutrient limitation and, simultaneously, attract arbuscular mycorrhizal fungi (AMF) for establishing beneficial symbiosis. Based on their chemical structure, SLs are designated as either canonical or non-canonical; however, the question of whether the two classes are also distinguished in their biological functions remained largely elusive until recently. In this review we summarize the latest advances in SL biosynthesis and highlight new findings pointing to rhizospheric signaling as the major function of canonical SLs."
Authors: Fereshteh Jafari, Baobao Wang, Haiyang Wang and Junjie Zou.
Journal of Integrative Plant Biology (2023)
Abstract: "Maize is a major staple crop widely used as food, animal feed, and raw materials in industrial production. High-density planting is a major factor contributing to the continuous increase of maize yield. However, high planting density usually triggers a shade avoidance response and causes increased plant height and ear height, resulting in lodging and yield loss. Reduced plant height and ear height, more erect leaf angle, reduced tassel branch number, earlier flowering, and strong root system architecture are five key morphological traits required for maize adaption to high-density planting. In this review, we summarize recent advances in deciphering the genetic and molecular mechanisms of maize involved in response to high-density planting. We also discuss some strategies for breeding advanced maize cultivars with superior performance under high-density planting conditions."
Authors: Huwei Sun, Hanyun Wang and Chengcai Chu.
Science China - Life Sciences (2024)
Excerpt: "An earlier study has demonstrated that SL biosynthesis requires the symbiotic GRAS type transcription factors NODULATION SIGNALING PATHWAY 1 NSP1 and NSP2 in Medicago truncatula and rice (Liu et al., 2011). Very recently, Yuan et al. (2023) revealed the upstream transcription factors of SL bio synthesis and the molecular mechanism by which SLs regulate N-P balance in response to LP. Under LP conditions, the central P signaling regulator PHOSPHATE STARVATION RESPONSE (OsPHR2) directly activated the expression of NSP1, NSP2, and SL biosynthesis genes D27, D17 and Os900 in rice. NSP1 and NSP2 further formed heterodimers and activated the expression of SL biosynthesis genes (D27, D17, D10, Os900 and Os1400), leading to elevated SL s levels in rice roots and root exudates under Pi deficient conditions . Moreover, the SLs levels in nsp1, nsp2 and nsp1 nsp2 double mutants under LP were similar to or only several fold those in WT plants under high P (HP) conditions, demonstrating that NSP1 and NSP2 are essential for SL biosynthesis under LP conditions. SLs further activated their signaling pathways, promoting the expression of the tillering suppressor TEOSINTE BRANCHED 1 (OsTB1) and thus reducing tiller numbers. To elucidate the mechanisms by which SLs regulate root development and nutrient absorption, Yuan et al. (2023) identified the early SL responsive genes in rice roots using the SL synthetic analogs GR24 4DO and GR24 5DS , which specifically activated the SL signaling pathway. Based on the RNA seq results, the authors identified 150 upregulated genes and 168 downregulated genes, which were commonly regulated by both GR24 and LP treatments. Among the genes repressed by GR24 and LP supply, CROWN ROOTLESS 1 (CRL1)/ADVENTITIOUS ROOTLESS 1 (ARL1) was a newly identified early SL responsive gene. And its expression was inhibited by the activation of the NSP1/2 SL signaling pathway, leading to a reduction in lateral root density of rice under LP conditions (Figure 1)."
Authors: Moritz Göbel and Franziska Fichtner.
Journal of Plant Physiology (2023)
Abstract: "Plants exhibit enormous plasticity in regulating their architecture to be able to adapt to a constantly changing environment and carry out vital functions such as photosynthesis, anchoring, and nutrient uptake. Phytohormones play a role in regulating these responses, but sugar signalling mechanisms are also crucial. Sucrose is not only an important source of carbon and energy fuelling plant growth, but it also functions as a signalling molecule that influences various developmental processes. Trehalose 6-phosphate (Tre6P), a sucrose-specific signalling metabolite, is emerging as an important regulator in plant metabolism and development. Key players involved in sucrose and Tre6P signalling pathways, including MAX2, SnRK1, bZIP11, and TOR, have been implicated in processes such as flowering, branching, and root growth. We will summarize our current knowledge of how these pathways shape shoot and root architecture and highlight how sucrose and Tre6P signalling are integrated with known signalling networks in shaping plant growth."
Authors: Abdugaffor Ablazov, Muhammad Jamil, Imran Haider, Jian You Wang, Vanessa Melino, Moez Maghrebi, Gianpiero Vigani, Kit Xi Liew, Pei-Yu Lin, Guan-Ting Chen, Hendrik NJ Kuijer, Lamis Berqdar, Teresa Mazzarella, Valentina Fiorilli, Luisa Lanfranco, Xiongjie Zheng, Nai-Chiang Dai, Ming-Hsin Lai, Yue-Ie Caroline Hsing, Mark Tester, Ikram Blilou and Salim Al-Babili.
bioRxiv (2023)
Abstract: "The rice Zaxinone Synthase (ZAS) gene encodes a carotenoid cleavage dioxygenase (CCD) that forms the apocarotenoid growth regulator zaxinone. Here, we generated and characterized constitutive ZAS-overexpressing rice lines, to better understand ZAS role in determining zaxinone content and regulating growth and architecture. ZAS overexpression enhanced endogenous zaxinone level, promoted root growth and meristem size, and increased the number of productive tillers, leading to an up to 30% higher grain yield per plant. Hormone analysis revealed a decrease in strigolactone (SL) content, which we confirmed by rescuing the high-tillering phenotype through application of a SL analog. Metabolomics analysis revealed that ZAS overexpressing plants accumulate higher amounts of monosaccharide sugars, in line with transcriptome analysis. Moreover, transgenic plants showed higher carbon (C) assimilation rate and elevated root phosphate, nitrate and sulfate level, enhancing the tolerance towards low phosphate (Pi) and indicating a generally better nutrient uptake. Our study shows that ZAS regulates hormone homeostasis and a combination of physiological processes to promote growth and grain yield, which makes this gene an excellent candidate for sustainable crop improvement."
Authors: Guan-Ting Erica Chen, Jian You Wang, Cristina Votta, Justine Braguy, Muhammad Jamil, Gwendolyn K. Kirschner, Valentina Fiorilli, Lamis Berqdar, Aparna Balakrishna, Ikram Blilou, Luisa Lanfranco and Salim Al-Babili.
PNAS (2023)
Significance: Strigolactones (SLs) are multifunctional, structurally diverse secondary metabolites fulfilling the function of a hormone. Whether a particular SL exerts specific functions is one of the most important questions in SL biology. Here, we generated and characterized rice mutants lacking the common SLs 4-deoxyorobanchol and/or its derivative orobanchol, which represent one of the two SL subfamilies, i.e., canonical SLs. We show that 4-deoxyorobanchol is not a determinant of shoot branching, but has a specific function as a regulator of shoot, root, and panicle growth. Accumulation of 4-deoxyorobanchol affects auxin homeostasis and negatively impacts the symbiosis with mycorrhizal fungi. Our data reveal specific hormonal functions of canonical SLs and pave the way for targeted modulation of rice architecture and rhizospheric interactions.
Abstract: "Strigolactones (SLs) regulate many developmental processes, including shoot-branching/tillering, and mediate rhizospheric interactions. SLs originate from carlactone (CL) and are structurally diverse, divided into a canonical and a noncanonical subfamily. Rice contains two canonical SLs, 4-deoxyorobanchol (4DO) and orobanchol (Oro), which are common in different plant species. The cytochrome P450 OsMAX1-900 forms 4DO from CL through repeated oxygenation and ring closure, while the homologous enzyme OsMAX1-1400 hydroxylates 4DO into Oro. To better understand the biological function of 4DO and Oro, we generated CRISPR/Cas9 mutants disrupted in OsMAX1-1400 or in both OsMAX1-900 and OsMAX1-1400. The loss of OsMAX1-1400 activity led to a complete lack of Oro and an accumulation of its precursor 4DO. Moreover, Os1400 mutants showed shorter plant height, panicle and panicle base length, but no tillering phenotype. Hormone quantification and transcriptome analysis of Os1400 mutants revealed elevated auxin levels and changes in the expression of auxin-related, as well as of SL biosynthetic genes. Interestingly, the Os900/1400 double mutant lacking both Oro and 4DO did not show the observed Os1400 architectural phenotypes, indicating their being a result of 4DO accumulation. Treatment of wild-type plants with 4DO confirmed this assumption. A comparison of the Striga seed germinating activity and the mycorrhization of Os900, Os900/1400, and Os1400 loss-of-function mutants demonstrated that the germination activity positively correlates with 4DO content while disrupting OsMAX1-1400 has a negative impact on mycorrhizal symbiosis. Taken together, our paper deciphers the biological function of canonical SLs in rice and reveals their particular contributions to establishing architecture and rhizospheric communications."
Authors: Kun Yuan, Hao Zhang, Chaoji Yu, Nan Luo, Jijun Yan, Shuang Zheng, Qingling Hu, Dahan Zhang, Liquan Kou, Xiangbing Meng, Yanhui Jing, Mingjiang Chen, Xinwei Ban, Zongyun Yan, Zefu Lu, Jian Wu, Yu Zhao, Yan Liang, Yonghong Wang, Guosheng Xiong, Jinfang Chu, Ertao Wang, Jiayang Li and Bing Wang.
Molecular Plant (2023)
Abstract: "Phosphorus is an essential macronutrient for plant development and metabolism. Plants have evolved ingenious mechanisms to overcome phosphate (Pi) starvation. However, the molecular mechanisms underlying regulation of shoot and root architectures as well as coordinated utilization of Pi and nitrogen remain largely unclear. Here, we show that Nodulation Signaling Pathway 1 (NSP1) and NSP2 regulate tiller number by promoting the biosynthesis of strigolactones (SLs), which are a class of phytohormones with fundamental effects on plant architecture and environmental responses. We found that in response to low-Pi stress, NSP1 and NSP2 are induced by Oryza sativa PHOSPHATE STARVATION RESPONSE2 (OsPHR2) and form a complex to directly bind the promoters of SL biosynthesis genes, leading to a great promotion on SL biosynthesis in rice. Interestingly, the NSP1/2-SL signaling module represses the expression of CROWN ROOTLESS 1 (CRL1), a newly identified early SL responsive gene in roots, to restrain lateral root density under Pi deficiency. Furthermore, we demonstrated that GR244DO treatment under normal conditions could repress the expression of OsNRTs and OsAMTs to suppress nitrogen absorption but enhance the expression of OsPTs to promote Pi absorption, thus facilitating the balance of nitrogen and phosphorus uptake in rice. Importantly, we found that the NSP1p:NSP1 and NSP2p:NSP2 transgenic plants showed improved agronomic traits and grain yield under low and medium phosphorus conditions. Taken together, these results uncovered the mechanisms of SL biosynthesis and signaling in response to Pi starvation stress, providing genetic resources for improving plant architecture and nutrient use efficiency under low Pi environments."
Authors: Rameshwar Sharma and Yellamaraju Sreelakshmi.
Journal of Experimental Botany (2023)
Abstract: "Axillary buds (ABs) are dormant buds located in the leaf axils of plants, which have the potential to develop into branches or flowers under appropriate conditions. At the molecular-genetic level, the miR156/SPL/SPB module regulates the development of ABs in plants, thus influencing plant architecture. Auxins are plant hormones that regulate various aspects of plant growth and development, including AB activity. Barrera-Rojas et al. (2023) show that suppressing AB outgrowth elevates auxin levels and lowers GOBLET expression, probably by suppressing its transcription by SBP15. Their findings provide insights into the regulation of AB outgrowth and tomato shoot architecture."
Authors: Jun Wang, Jing Huang, Jinlin Bao, Xizhi Li, Liang Zhu and Jian Jin.
Molecular Plant (2023)
Abstract: "Plant architecture and panicle architecture are two critical agronomic traits that largely affect the yield of rice (Oryza sativa L.). PROSTRATE GROWTH 1 (PROG1) encodes a key C2H2-type zinc-finger transcription factor and has pleiotropic effects on the regulation of both plant and panicle architecture, thereby influencing the grain yield. However, the molecular mechanisms through which PROG1 controls plant and panicle architecture remain unclear. In this study, we have demonstrated the direct binding of PROG1 to the LAZY 1 (LA1) promoter and its role as a repressor of LA1. Conversely, LA1 acts as a repressor of PROG1 by directly binding to the PROG1 promoter. These two genes play antagonistic roles in shaping plant architecture by regulating both tiller angle and tiller number. Furthermore, our findings reveal that PROG1 controls panicle architecture through direct binding to the intragenic regulatory regions of OsGIGANTEA (OsGI) and subsequent activation of its expression. Overall, our study has identified two crucial targets of PROG1, LA1 and OsGI, shedding light on the primary molecular mechanisms underlying plant and panicle architecture control by PROG1. This provides valuable insights into the regulation of key domestication-related traits in rice and identifies potential targets for future high-yield rice breeding."
Authors: Xing Liu, Daniel P. Wickland, Zhicong Lin, Quilin Liu, Lucas Borges Dos Santos, Karen A. Hudson and Matthew E. Hudson.
Journal of Experimental Botany (2023)
Abstract: "Height is a critical component of plant architecture, significantly affecting crop yield. The genetic basis of this trait in soybean remains unclear. In this study, we report the characterization of the Compact mutant of soybean, which has short internodes. The candidate gene was mapped to chromosome 17, and the interval containing the causative mutation was further delineated using biparental mapping. Whole-genome sequencing of the mutant revealed an 8.7 kb deletion in the promoter of the Glyma.17g145200 gene, which encodes a member of the class III gibberellin (GA) 2-oxidases. The mutation has a dominant effect, likely via increased expression of the GA 2-oxidase transcript observed in green tissue, as a result of the deletion in the promoter of Glyma.17g145200. We further demonstrate that levels of GA precursors are altered in the Compact mutant, supporting a role in GA metabolism, and that the mutant phenotype can be rescued with exogenous GA3. We also determined that overexpression of Glyma.17g145200 in Arabidopsis results in dwarfed plants. Thus, gain of promoter activity in the Compact mutant leads to a short internode phenotype in soybean through altered metabolism of gibberellin precursors. These results provide an example of how structural variation can control an important crop trait and a role for Glyma.17g145200 in soybean architecture, with potential implications for increasing crop yield."
Authors: Hongxiang Lou, Bowen Zhao, Yan Peng, Ali Mahmoud El-Badri, Maria Batool, Chunyun Wang, Zongkai Wang, Wei Huang, Tianyao Wang, Zhen Li, Zhenghua Xu, Jing Wang, Bo Wang, Jie Kuai and Guangsheng Zhou.
Field Crops Research (2023)
Highlights • Various plant architecture rapeseeds responded differently to nitrogen and density. • HS5+/sca was suitable for reducing nitrogen rate and increasing plant density. • BnaA3. IAA7 mutation caused more lateral roots and root biomass in HS5+/sca. • Auxin level and its signaling genes expression affected root-crown growth.
Abstract: "Context - With the increasing global food and oil security problems, improvement in rapeseed (Brassica napus L.) yield become urgent. Moreover, previous studies rarely used the semi-dwarf and compact plant type of rapeseed to improve yield potential. Objective - Herein, we aimed to investigate the effects of different nitrogen application rates and plant density on root growth and yield-related traits using three genotypes with different plant types to clarify various regulatory mechanisms using semi-dwarf and compact plant type mutants to achieve high yield. Methods - Split-split-plot experiments with three nitrogen application rates (N1: N2: N3, 120: 240: 360 kg ha−1) and three plant densities (D1: D2: D3, 15 × 104: 45 × 104: 75 × 104 plants·ha−1) were conducted during the three growing seasons (2019–2022) using semi-dwarf mutant HS5sca, and HS5 (wild type) as well as their F1 hybrid HS5+/sca. Results - With decreasing nitrogen application rate (N3 to N2), the expression level of IAA signal response genes BnaA07. GH3 and BnaA03. IAA13 was decreased in root, while increased in shoot at the early-flowering stage. Moreover, IAA content was decreased in roots and aboveground parts, whereas soluble sugar content of root bleeding sap was increased and volume of root bleeding sap was decreased in three genotypes at early-flowering stage. Additionally, nitrogen accumulation per plant and yield per plant was decreased, while population nitrogen accumulation and population yield were increased with decreasing nitrogen application rate in three studied genotypes. On the other side, with increasing plant density, the expression of BnaA07. GH3 and BnaA03. IAA13 genes were first increased and then decreased in root tissues. In addition, root surface area, the total volume of root bleeding sap, and nitrogen accumulation were decreased, which decreased dry matter and yield per plant. However, total root area, population nitrogen accumulation, and population yield in the three genotypes were increased, and yield was the highest at D2. The population yield of HS5sca, HS5+/sca, and HS5 achieved the largest increase of 26.0%, 10.3%, and 9.5% under N2D2 in 2019, 6.9%, 8.4%, and 4.7% under N3D2 in 2020, respectively, as compared to N3D1. Moreover, the morphological indices of HS5+/sca were greater than other genotypes, with the highest population yield. Conclusions - Appropriate nitrogen application rate with plant density optimized the root architecture and aboveground type of HS5+/sca that improved auxin level through affecting the downstream auxin-related genes, as well as improved dry matter accumulation and distribution, which increased yield potential. Compared with the two parents, F1 genotype HS5+/sca was suitable for nitrogen fertilizer (240 kg ha−1) and plant density (45–75 × 104 plants ha−1). Implications - + /sca heterozygous genotypes might promote root growth under low nitrogen application rate and high plant density. A strong root system is an important guarantee of high yield; thus, this heterozygous site could use to introduce excellent hybrids in rapeseed production to further improve root traits and optimize cultivation factors to increase seed yield.
Authors: Francois Barbier, Franziska Fichtner and Christine Beveridge.
Nature Plants (2023)
Editor's view: This Review summarizes recent knowledge and offers new insight about the role of strigolactone signalling in the integration of nutritional and metabolic status, as well as its consequences for plant development and architecture.
Abstract: "Strigolactones are rhizosphere signals and phytohormones that play crucial roles in plant development. They are also well known for their role in integrating nitrate and phosphate signals to regulate shoot and root development. More recently, sugars and citrate (an intermediate of the tricarboxylic acid cycle) were reported to inhibit the strigolactone response, with dramatic effects on shoot architecture. This Review summarizes the discoveries recently made concerning the mechanisms through which the strigolactone pathway integrates sugar, metabolite and nutrient signals. We highlight here that strigolactones and MAX2-dependent signalling play crucial roles in mediating the impacts of nutritional and metabolic cues on plant development and metabolism. We also discuss and speculate concerning the role of these interactions in plant evolution and adaptation to their environment."
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