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Authors: Tian Su, Ziwei Li, Yinghua Zhang, Junqiang Xu and Bin Xu.
Journal of the American Society for Horticultural Science (2024)
Abstract: "Cucumber (Cucumis sativus L.) belongs to the cucumber genus of the Cucurbitaceae family, and the selection of cultivars with minimal or no lateral branches can enhance the cultivation management efficiency. The growth of lateral branches is inhibited by strigolactone. To investigate the regulatory mechanism of strigolactone on the lateral branch development in cucumber, the cultivar LZ1 exhibiting multiple lateral branches was selected as the experimental material. The axillae of the plants were infiltrated with 1, 5, and 10 μmol·L−1 germination releaser 24 (GR24) at the four- to five-leaf stage. It was identified that 1 μmol·L−1 GR24 exhibited the most potent inhibitory effect on cucumber lateral branches. Additionally, exogenous strigolactone decreased the auxin content in the apical bud and axillae and increased the auxin content in the stem. This inhibited polar auxin transport in the axillary bud and promoted polar auxin transport in the apical bud. The content of strigolactone in the axilla region of cucumbers was elevated, whereas the synthesis and expression of cytokinin in the same area were reduced. A low concentration of GR24 induced the expression of cucumber branched 1 (csbrc1), whereas a high concentration of GR24 downregulated the expression of cucumber lateral suppressor (cscls) and blind (csblind), which inhibited the growth of cucumber lateral branches."
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: 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: 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: 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: WEN Yun-ze, HE Peng, BAI Xiao-han, ZHANG Hui-zhi, ZHANG Yun-feng and YU Jia-ning.
Journal of Integrative Agriculture (2023)
Abstract: "Cotton is one of the most important economic crops in the world and is a major source of fiber in the textile industry. Strigolactones (SLs) are a class of carotenoid-derived plant hormones involved in many processes of plant growth and development; however, SL functions in fiber development remain largely unknown. Here, we found that the endogenous SLs were significantly higher in fibers 20 days post-anthesis (DPA). Exogenous SLs significantly increased fiber length and cell wall thickness. Furthermore, we cloned three key SLs biosynthetic genes, namely GhD27, GhMAX3, and GhMAX4, which were highly expressed in fibers, and subcellular localization analyses revealed that GhD27, GhMAX3, and GhMAX4 were localized in the chloroplast. The exogenous expression of GhD27, GhMAX3, and GhMAX4 complemented the physiological phenotypes of d27, max3, and max4 mutations in Arabidopsis, respectively. Knockdown of GhD27, GhMAX3, and GhMAX4 in cotton resulted in an increased number of axillary buds and leaves, decreased fiber length, and significantly reduced fiber thickness. These findings revealed that SLs participate in plant growth, fiber elongation, and secondary cell wall formation in cotton. These results provide new and effective genetic resources for improving cotton fiber yield and plant architecture."
Authors: Mohammad Faizan, Shi Hui Cheng, Sadia Haque Tonny and Merajul Islam Robab.
Plant Physiology and Biochemistry (2022)
Highlights • Phytohormones play roles inter-connectedly and follow the mechanism of crosstalk signaling. • SLs termed as ‘ecological signal’ has shown a potential role towards the plant growth. • SLs helps to contribute to the removal of weed. • SLs along with other phytohormones imply roles in plant defense mechanism against abiotic stress.
Abstract: "Strigolactones (SLs) have been implicated in various developmental processes of the plant, including the response against several abiotic stresses. It is well known as a class of endogenous phytohormones that regulates shoot branching, secondary growth and root morphology. This hormone facilitates plants in responding to nitrogen and phosphorus starvation by shaping the above and below ground structural design. SLs actively participate within regulatory networks of plant stress adaptation that are governed by phytohormones. Heavy metals (HMs) in soil are considered a serious environmental problem that causes various harmful effects on plants. SLs along with other plant hormones imply the role in plant architecture is far from being fully understood. Strategy to remove/remediation of HMs from the soil with the help of SLs has not been defined yet. Therefore, the present review aims to comprehensively provide an overview of SLs role in fine-tuning plant architectures, relation with other plant hormones under abiotic stress, and remediation of HMs contaminated soil using SLs."
Authors: Kaori Yoneyama, Xiaonan Xie, Takahito Nomura, Koichi Yoneyama and Tom Bennett.
Current Biology (2022)
Editor's view: Strigolactones (SLs) trigger parasitism and symbiosis in the rhizosphere and function as a hormone in plants. Yoneyama et al. demonstrate that rice plants sense SLs in the rhizosphere and regulate their SL biosynthesis and exudation, suggesting that SLs act as a cue for a plant-plant communication in rice plants.
Highlights: • Crowding reduces biosynthesis and exudation of strigolactones • This density-dependent response requires strigolactone perception • Strigolactone biosynthesis and exudation respond to environmental strigolactones • Crowding in soil reduces strigolactone exudation and shoot branching in rice plants
Abstract: "Plants have evolved elaborate mechanisms to detect neighboring plants, which typically involve the perception of “cues” inadvertently produced by the neighbor.1 Strigolactones are hormonal signaling molecules2,3 that are also exuded into the rhizosphere by most flowering plant species to promote arbuscular mycorrhizal symbioses.4 Since flowering plants have an endogenous perception system for strigolactones,5 strigolactones are obvious candidates to act as a cue for neighbor presence, but have not been shown to act as such. To test this hypothesis in rice plants, we quantified two major strigolactones of rice plants, orobanchol and 4-deoxyorobanchol, in root exudates by using LC-MS/MS (MRM) and examined feedback regulation of strigolactone biosynthesis and changes in shoot branching phenotypes in rice plants grown at different densities in hydroponics and soil culture. We show that the presence of neighboring plants, or greater root volume, results in rapidly induced changes in strigolactone biosynthesis, sensitivity, and exudation and the subsequent longer-term changes in shoot architecture. These changes require intact strigolactone biosynthesis in neighboring plants and intact strigolactone signaling in focal plants. These results suggest that strigolactone biosynthesis and exudation in rice plants are driven by supra-organismal environmental strigolactone levels. Strigolactones thus act as a cue for neighbor presence in rice plants, but also seem to act as a more general root density-sensing mechanism in flowering plants that integrates soil volume and neighbor density and allows plants to adapt to the limitations of the rhizosphere."
Authors: Valentina Dell’Oste, Francesca Spyrakis and Cristina Prandi.
Molecules (2021)
Abstract: "Strigolactones (SLs) are a class of sesquiterpenoid plant hormones that play a role in the response of plants to various biotic and abiotic stresses. When released into the rhizosphere, they are perceived by both beneficial symbiotic mycorrhizal fungi and parasitic plants. Due to their multiple roles, SLs are potentially interesting agricultural targets. Indeed, the use of SLs as agrochemicals can favor sustainable agriculture via multiple mechanisms, including shaping root architecture, promoting ideal branching, stimulating nutrient assimilation, controlling parasitic weeds, mitigating drought and enhancing mycorrhization. Moreover, over the last few years, a number of studies have shed light onto the effects exerted by SLs on human cells and on their possible applications in medicine. For example, SLs have been demonstrated to play a key role in the control of pathways related to apoptosis and inflammation. The elucidation of the molecular mechanisms behind their action has inspired further investigations into their effects on human cells and their possible uses as anti-cancer and antimicrobial agents."
Authors: Matija Stanic, Neil M.N. Hickerson, Rex Arunraj and Marcus A. Samuel.
Plant Biotechnology Journal (2021)
Excerpts: "One group of hormones that is required for suppressing shoot branching and regulating axillary meristem activity are the Strigolactones (SLs), a class of carotenoid-derived terpenoid lactones (Umehara et al., 2008)."
"Given that yield increase in canola (Brassica napus) is a major industry priority, alteration of SL signaling could lead to a highly branched morphotype similar to the dwarfed plants of the green revolution with favorable shoot architecture for addition of more inputs. In order to examine if suppression of D14 receptor could lead to these desired changes, canola (Westar) were transformed with an RNAi suppression construct driven by the 35SCaMV promoter which targets the SL receptor BnD14."
"All T1 CRISPR/Cas9-edited lines exhibited a similar branched phenotype (Figure 1i) and sequencing showed consistent edits at the specified target sites and therefore T2 and T3 seeds from a single line, designated d14, was chosen for further downstream analyses. When SL biosynthetic genes were examined in the roots of d14 plants, characteristic feedback upregulation of CCD7 and CCD8 transcripts were observed in the absence strigolactone perception (Figure 1j)."
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Authors: Yuqi Liu, Shangyu Chen, Sikander Pal, Jingquan Yu, Yanhong Zhou, Lam-Son Phan Tran and Xiaojian Xia.
New Crops (2024)
Abstract: "Plants have evolved varied structures for environmental adaptation. Shoot branching, as a part of plant architecture, influences the allocation of sugars produced by photosynthesis and thus greatly impacts crop yields. The activity of axillary meristem, and apical dominance governs the shoot branching patterns. In this review, we summarize the key factors involved in the formation of lateral branches, and the mechanisms of how these factors are interconnected. In particular, we focus on recent advances in understanding how sugar and environmental signals affect the hormonal signaling network to regulate apical dominance. Ultimately, we propose that epigenetic modifications are critical mechanisms underlying the plasticity of shoot branching, and that precise targeted gene editing is promising for shaping the ideal plant architecture."
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: 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: 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: 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."
Authors: Tengkui Chen, Wuming Xiao, Cuihong Huang, Danhua Zhou, Yongzhu Liu, Tao Guo, Zhiqiang Chen and Hui Wang.
Plants (2023)
Abstract: "The plant architecture of rice is an important factor affecting yield. Strigolactones (SLs) are newly discovered carotenoid-derived plant hormones that play an important role in rice plant architecture. In this study, a high-tillering dwarf mutant, CHA-1, was identified by spatial mutagenesis. CHA-1 was located in the region of 31.52–31.55 MB on chromosome 1 by map-based cloning. Compared with the wild-type THZ, the CHA-1 mutant showed that ACCAC replaced TGGT in the coding region of the candidate gene LOC_Os01g54810, leading to premature termination of expression. Genetic complementation experiments proved that LOC_Os01g54810 was CHA-1, which encodes a putative member of Class III lipase. Expression analysis showed that CHA-1 was constitutively expressed in various organs of rice. Compared with those in THZ, the expression levels of the D17 and D10 genes were significantly downregulated in the CHA-1 mutant. In addition, the concentrations of ent-2′-epi-5-deoxystrigol (epi-5DS) in the root exudates of the CHA-1 mutant was significantly reduced compared with that of THZ, and exogenous application of GR24 inhibited the tillering of the CHA-1 mutant. These results suggest that CHA-1 influences rice architecture by affecting SL biosynthesis."
Authors: Sirisha Kaniganti, Joorie Bhattacharya, Petla Bhanu Prakash and Palakolanu Sudhakar Reddy.
Environmental and Experimental Botany (2022)
Highlights: • SL plays a crucial role in host-parasite interaction. • SL functions in root and shoot architecture regulation, nutrition uptake. • Involved in physiological responses of the plant with phytohormones. • Regulate developmental processes like root hair elongation, leaf senescence. • Play a vital role in biotic and abiotic stress tolerance.
Abstract: "Strigolactones (SLs), initially reported as germination stimulants for Striga lutea were later described for their role in Phelipanche and Orobanche species. SLs were reported in major cereals such as sorghum and maize, which established their importance in host-parasite interaction. Over the past decade, several roles of SLs have been elucidated in root and shoot architecture, pathogen interaction, plant defense mechanism, and nutrition uptake. Additionally, SL plays a key role in abiotic and biotic stress tolerance associated with other phytohormones. The review provides a comprehensive overview of various aspects of SLs and their complex interaction networks with other phytohormones, including ethylene, that exist in the plant system. The review also highlights pivotal points for establishing SLs in commercial agriculture to fully explore their potential in crop improvement and shaping modern agriculture."
Authors: Khopeno Khuvung, Federico A. O. Silva Gutierrez and Didier Reinhardt.
Frontiers in Plant Science (2022)
Abstract: "Despite its central role in the control of plant architecture, strigolactone has been recognized as a phytohormone only 15 years ago. Together with auxin, it regulates shoot branching in response to genetically encoded programs, as well as environmental cues. A central determinant of shoot architecture is apical dominance, i.e., the tendency of the main shoot apex to inhibit the outgrowth of axillary buds. Hence, the execution of apical dominance requires long-distance communication between the shoot apex and all axillary meristems. While the role of strigolactone and auxin in apical dominance appears to be conserved among flowering plants, the mechanisms involved in bud activation may be more divergent, and include not only hormonal pathways but also sugar signaling. Here, we discuss how spatial aspects of SL biosynthesis, transport, and sensing may relate to apical dominance, and we consider the mechanisms acting locally in axillary buds during dormancy and bud activation."
Authors: Liping Zhu, Lingling Dou, Huizhi Zhang, Li Zhang, Cuixia Liu, Jianing Yu and Guanghui Xiao.
Research Square (2021)
Abstract: "Strigolactone (SL) signaling is essential in regulating plant development. DWARF14 (D14), the SL receptor, interacts with the F-box in MORE AXILLARY GROWTH (MAX2) to modulate SL signaling. However, the biological function of D14 protein is still unknown in cotton. Here, we identified GhD14s in Gossypium hirsutum and resolved its function in cotton plant architecture and fiber development. The GhD14D protein was localized to both the cytoplasm and nucleus. GUS staining assay showed that GhD14D was mainly expressed in leaf primordium, inflorescence, axillary bud and stem and expression analysis revealed that GhD14A/D was highly expressed in stem, flower and fiber cells at 20 days post-anthesis (DPA). Silencing GhD14A/D gene expression in upland cotton significantly increased branch angle and reduced fiber length as well as the transcripts of secondary cell wall biosynthesis related genes. In addition, overexpression of GhD14D in Atd14 mutant successfully rescued the phenotype of the d14-1 mutant with much shoot-branching and short plant height. Our findings suggest that the GhD14 gene contributes to shoot branch development and fiber cell development in cotton. This study deepens our understanding of the biological role of SL signaling in cotton and providing guidance for modifying cotton plant architecture and improving fiber development using genetic engineering to help us breed better cotton varieties in the future."
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