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Authors: Joseph Cammarata, Adrienne H. K. Roeder and Michael J. Scanlon.
bioRxiv (2022)
Abstract: "Crosstalk between auxin and cytokinin contributes to widespread developmental processes, including root and shoot meristem maintenance, phyllotaxy, and vascular patterning. Although auxin and cytokinin are potent regulators of plant development, our understanding of crosstalk between these hormones is limited to few model systems. The moss Physcomitrium patens (formerly Physcomitrella patens) is a powerful system for studying plant hormone function. Auxin and cytokinin play similar roles in regulating moss gametophore (upright shoot) architecture, as they do in flowering plant shoots. However, auxin-cytokinin crosstalk is poorly understood in moss. Here we find that the ratio of auxin to cytokinin is an important determinant of development in P. patens, especially during leaf development and branch stem cell initiation. Addition of high levels of auxin to P. patens gametophores blocks leaf outgrowth. However, simultaneous addition of high levels of both auxin and cytokinin partially restores leaf outgrowth, suggesting that the ratio of these hormones is the overriding factor. Likewise, during branch initiation and outgrowth, chemical inhibition of auxin synthesis phenocopies cytokinin application. Finally, cytokinin insensitive mutants resemble plants with altered auxin signaling and are hypersensitive to auxin. In summary, our results suggest that the ratio between auxin and cytokinin signaling is the basis for developmental decisions in the moss gametophore."
Authors: Batist Geldhof, Jolien Pattyn, Petar Mohorović, Karlien Van den Broeck, Vicky Everaerts, Ondřej Novák and Bram Van de Poel.
bioRxiv (2022)
Abstract: "Developing leaves undergo a vast array of age-related changes as they mature. These include physiological, hormonal and morphological changes that determine their adaptation plasticity towards adverse conditions. Waterlogging induces leaf epinasty in tomato, and the magnitude of leaf bending is intricately related to the age-dependent cellular and hormonal response. We now show that ethylene, the master regulator of epinasty, is differentially regulated throughout leaf development, giving rise to age-dependent epinastic responses. Young leaves have a higher basal ethylene production, but are less responsive to waterlogging-induced epinasty, as they have a higher capacity to convert the root-borne and mobilized ACC into the inactive conjugate MACC. Ethylene stimulates cell elongation relatively more at the adaxial petiole side, by activating auxin biosynthesis and locally inhibiting its transport through PIN4 and PIN9 in older and mature leaves. As a result, auxins accumulate in the petiole base of these leaves and enforce partially irreversible epinastic bending upon waterlogging. Young leaves maintain their potential to transport auxins, both locally and through the vascular tissue, leading to enhanced flexibility to dampen the epinastic response and a faster upwards repositioning during reoxygenation. This mechanism also explains the observed reduction of epinasty during and its recovery after waterlogging in the anthocyanin reduced (are) and Never ripe (Nr) mutants, both characterized by higher auxin flow. Our work has demonstrated that waterlogging activates intricate hormonal crosstalk between ethylene and auxin, controlled in an age-dependent way."
Authors: Janlo M. Robil and Paula McSteen.
New Phytologist (2023)
Abstract: "Parallel veins are characteristic of monocots, including grasses (Poaceae). Therefore, how parallel veins develop as the leaf grows in the medial-lateral (ML) dimension is a key question in grass leaf development. Using fluorescent protein reporters, we mapped auxin, cytokinin (CK), and gibberellic acid (GA) response patterns in maize (Zea mays) leaf primordia. We further defined the roles of these hormones in ML growth and vein formation through combinatorial genetic analyses and measurement of hormone concentrations. We discovered a novel pattern of auxin response in the adaxial protoderm that we hypothesize has important implications for the orderly formation of 3° veins early in leaf development. In addition, we found an auxin transport and response pattern in the margins that correlates with the transition from ML to PD growth. We present evidence that auxin efflux precedes CK response in procambial strand development. We also determined that GA plays an early role in the shoot apical meristem as well as a later role in the primordium to restrict ML growth. We propose an integrative model whereby auxin regulates ML growth and vein formation in the maize leaf through control of GA and CK."
Authors: Jinlei Sui, Xiaohu Xiao, Jianghua Yang, Yujie Fan, Sirui Zhu, Jinheng Zhu, Binhui Zhou, Feng Yu and Chaorong Tang.
Plant Science (2023)
Highlights: • Four latex-abundant RALFs specifically interacted with the extracellular domain of HbFER1. • Bioactivity assays reveal functional conservation of latex-abundant HbRALFs. • The HbRALF-FER pathway implicates in regulation of pH homeostatis in Hevea latex. • Immunoinhibition of HbFER1 affects rubber biosynthesis.
Abstract: "RAPID ALKALINIZATION FACTORs (RALFs), which are secreted peptides serving as extracellular signals transduced to the inside of the cell, interact with the receptor-like kinase FERONIA (FER) and participates in various biological pathways. Here, we identified 23 RALF and 2 FER genes in Hevea brasiliensis (para rubber tree), and characterized their expression patterns in different tissues, across the process of leaf development, and in response to the rubber yield-stimulating treatments of tapping and ethylene. Four Hevea latex (the cytoplasm of rubber-producing laticifers)-abundant RALF isoforms, HbRALF19, HbRALF3, HbRALF22, and HbRALF16 were listed with descending expression levels. Of the four HbRALFs, expressions of HbRALF3 were markedly regulated in an opposite way by the treatments of tapping (depression) and ethylene (stimulation). All of the four latex-abundant RALFs specifically interacted with the extracellular domain of HbFER1. Transgenic Arabidopsis plants overexpressing these HbRALFs displayed phenotypes similar to those reported for AtRALFs, such as shorter roots, smaller plant architecture, and delayed flowering. The application of HbRALF3 and HbRALF19 recombinant proteins significantly reduced the pH of Hevea latex, an important factor regulating latex metabolism. An in vitro rubber biosynthesis assay in a mixture of latex cytosol (C-serum) revealed a positive role of HbFER1 in rubber biosynthesis. Taken together, these data provide evidence for the participation of the HbRALF-FER module in rubber production."
Authors: Huifang Li, Hong Liu, Chenyang Hao, Tian Li, Yunchuan Liu, Xiaolu Wang, Yuxin Yang, Jun Zheng and Xueyong Zhang.
Plant Physiology (2023)
Abstract: "Auxin plays an important role in regulating leaf senescence. Auxin response factors (ARFs) are crucial components of the auxin signaling pathway; however, their roles in leaf senescence in cereal crops are unknown. In this study, we identified TaARF15-A1 as a negative regulator of senescence in wheat (Triticum aestivum L.) by analyzing TaARF15-A1 overexpression and RNA interference lines and CRISPR/Cas9-based arf15 mutants. Overexpression of TaARF15-A1 delayed senescence, whereas knockdown lines and knockout mutants showed accelerated leaf senescence and grain ripening. RNA-seq analysis revealed that TaARF15-A1 delays leaf senescence by negatively regulating senescence-promoting processes and positively modulating senescence-delaying genes including senescence-associated phytohormone biosynthesis and metabolism genes as well as transcription factors. We also demonstrated that TaARF15-A1 physically interacts with TaMYC2, a core jasmonic acid (JA) signaling transcription factor that positively modulates wheat senescence. Furthermore, TaARF15-A1 suppressed the expression of TaNAM-1 (TaNAM-A1 and TaNAM-D1) via protein–protein interaction and competition with TaMYC2 for binding to its promoter to regulate senescence. Finally, we identified two haplotypes of TaARF15-A1 in global wheat collections. Association analysis revealed that TaARF15-A1-HapI has undergone strong selection during wheat breeding in China, likely owing to its earlier maturity. Thus, we identify TaARF15-A1 as a negative regulator of senescence in common wheat and present another perspective on the crosstalk between auxin and JA signaling pathways in regulating plant senescence."
Authors: Nguyen Manh Linh and Enrico Scarpella.
PLOS Biology (2022)
Editor's view: How do plants form vein networks, in the absence of cellular migration or direct cell-cell interaction? This study shows that a GNOM-dependent combination of polar auxin transport, auxin signal transduction, and movement of an auxin signal through plasmodesmata patterns leaf vascular cells into veins.
Abstract: "To form tissue networks, animal cells migrate and interact through proteins protruding from their plasma membranes. Plant cells can do neither, yet plants form vein networks. How plants do so is unclear, but veins are thought to form by the coordinated action of the polar transport and signal transduction of the plant hormone auxin. However, plants inhibited in both pathways still form veins. Patterning of vascular cells into veins is instead prevented in mutants lacking the function of the GNOM (GN) regulator of auxin transport and signaling, suggesting the existence of at least one more GN-dependent vein-patterning pathway. Here we show that in Arabidopsis such a pathway depends on the movement of auxin or an auxin-dependent signal through plasmodesmata (PDs) intercellular channels. PD permeability is high where veins are forming, lowers between veins and nonvascular tissues, but remains high between vein cells. Impaired ability to regulate PD aperture leads to defects in auxin transport and signaling, ultimately leading to vein patterning defects that are enhanced by inhibition of auxin transport or signaling. GN controls PD aperture regulation, and simultaneous inhibition of auxin signaling, auxin transport, and regulated PD aperture phenocopies null gn mutants. Therefore, veins are patterned by the coordinated action of three GN-dependent pathways: auxin signaling, polar auxin transport, and movement of auxin or an auxin-dependent signal through PDs. Such a mechanism of tissue network formation is unprecedented in multicellular organisms."
Authors: Huadong Zhan, Mingmin Lu, Qin Luo, Feng Tan, Ziwei Zhao, Mingqian Liu and Yubing He.
Plant Science (2022)
Highlights • Single and double mutants of OsCPD genes are constructed via CRISPR/Cas9 gene editing tool. • Oscpd1 oscpd2 double mutants develop multiple and obvious brassinosteroid-related defects. • Overexpression of OsCPD1 and OsCPD2 led to a typical brassinosteroid enhanced phenotype.
Abstract: "CONSTITUTIVE PHOTOMORPHOGENIC DWARF (CPD), member of the CYP90A family of cytochrome P450 (CYP450) monooxygenase, is an essential component of brassinosteroids (BRs) biosynthesis pathway. Compared with a single CPD/CYP90A1 in Arabidopsis thaliana, two highly homologous CPD genes, OsCPD1/CYP90A3 and OsCPD2/CYP90A4, are present in rice genome. There is still no genetic evidence so far about the requirement of OsCPD1 and OsCPD2 in rice BR biosynthesis. In this study, we reported the functional characterization of OsCPD genes using CRISPR/Cas9 gene editing technology. The overall growth and development of oscpd1 and oscpd2 single knock-out mutants was indistinguishable from the wild-type, whereas, the oscpd1 oscpd2 double mutant displayed multiple and obvious BR-related defects. Cytological analyses further indicated the defective cell elongation in oscpd1 oscpd2 double mutant. The oscpd double mutants had a lower endogenous BR level and could be restored by the application of the brassinolide (BL). Moreover, overexpression of OsCPD1 and OsCPD2 led to a typical BR enhanced phenotype, with enlarged leaf angle and increased grain size. Taken together, our results provide direct genetic evidence that OsCPD1 and OsCPD2 play essential and redundant roles in maintenance of plant architecture by modulating BR biosynthesis in rice."
Authors: Sergio Navarro-Cartagena and José Luis Micol.
Trends in Plant Science (2023)
Highlights: In simple leaves, like those of Arabidopsis thaliana, the positional information provided by auxin has been considered enough to explain leaf serration, which in addition requires the CUP-SHAPED COTYLEDON2 (CUC2) transcription factor. Cytokinin response and CUC2 localization coincide at the base of arabidopsis leaf primordia, and plants defective in cytokinin activity have leaf margins less serrated than the wild type. Cytokinins favor leaf complexity in the development of the compound leaves of Solanum lycopersicum and Cardamine hirsuta. Auxin and cytokinins crosstalk in different plant developmental processes; we hypothesize that cytokinins also play a role via their interplay with auxin in leaf margin morphogenesis of simple leaves.
Abstract: "The interplay between auxin and cytokinins affects facets of plant development as different as ovule formation and lateral root initiation. Moreover, cytokinins favor complexity in the development of Solanum lycopersicum and Cardamine hirsuta compound leaves. Nevertheless, no role has been proposed for cytokinins in patterning the margins of the simple leaves of Arabidopsis thaliana, a process that is assumed to be sufficiently explained by auxin localization. Here, we discuss evidence supporting the hypothesis that cytokinins play a role in simple leaf margin morphogenesis via crosstalk with auxin, as occurs in other plant developmental events. Indeed, mutant or transgenic arabidopsis plants defective in cytokinin biosynthesis or signaling, or with increased cytokinin degradation have leaf margins less serrated than the wild type."
Authors: Yingying Cao, Dandan Dou, Dongling Zhang, Yaogang Zheng, Zhenzhen Ren, Huihui Su, Chongyu Sun, Xiaomeng Hu, Miaomiao Bao, Bingqi Zhu, Tianxue Liu, Yanhui Chen and Lixia Ku.
Plant Science (2022)
Highlights: • To meet the demands for the projected 10 billion people by 2050, it is urgently needed improve crop yields through developing new breeding technologies. • Leaf angle (LA) is a key trait of plant architecture and a target for genetic improvement of crops. • In this study, we cloned the ZmDWF1 gene originated from our previous reported QTL qLA5-1 through map-based cloning. • Overexpression of ZmDWF1 resulted in enlarged LA, indicating that ZmDWF1 is a positive regulator of LA in maize, and the regulatory framework of ZmDWF1 was created based on the results from RNA-Sequencing and yeast-two hybrid (Y2H) screening analysis. • This study provides a comprehensive update on the progress of studying the molecular genetic mechanisms of LA formation in cereal crops and strategies for breeding cereal crops.
Abstract: "Leaf angle (LA) is a critical agronomic trait enhancing grain yield under high-density planting in maize. A number of researches have been conducted in recent years to investigate the quantitative trait loci/genes responsible for LA variation, while only a few genes were identified through map-based cloning. Here we cloned the ZmDWF1 gene, which was previously reported to encode Δ24-sterol reductase in the brassinosteroids (BRs) biosynthesis pathway. Overexpression of ZmDWF1 resulted in enlarged LA, indicating that ZmDWF1 is a positive regulator of LA in maize. To reveal the regulatory framework of ZmDWF1, we conducted RNA-Sequencing and yeast-two hybrid (Y2H) screening analysis. RNA-Sequencing analyzing results indicate ZmDWF1 mainly affected expression level of genes involved in cell wall associated metabolism and hormone metabolism including BR, gibberellin, and auxin. Y2H screening with Bi-FC assay confirmed three proteins (ZmPP2C-1, ZmROF1, and ZmTWD1) interacting with ZmDWF1. We revealed a new regulatory network of ZmDWF1 gene in controlling plant architecture in maize."
Authors: Peng Huang, Jiangzhe Zhao, Jiale Hong, Bao Zhu, Shuai Xia, Zhu Engao, Pingfei Han and Kewei Zhang.
Plant Physiology (2023)
Abstract "Leaf angle is determined by lamina joint inclination and is an important agronomic trait that determines plant architecture, photosynthetic efficiency, and crop yield. Cytokinins are phytohormones involved in shaping rice (Oryza sativa L.) architecture, but their role in leaf angle remains unknown. Here, we report that cytokinin accumulation mediated by rice CYTOKININ OXIDASE/DEHYDROGENASE3 (OsCKX3) controls lamina joint development and negatively regulates leaf angle. Phenotypic analysis showed that rice osckx3 mutants had smaller leaf angles, while the overexpression lines (OsCKX3-OE) had larger leaf angles. Histological sections indicated that the leaf inclination changes in the osckx3 and OsCKX3-OE lines resulted from asymmetric proliferation of the cells and vascular bundles in the lamina joint. Reverse transcription quantitative PCR, promoter-fused β-glucuronidase (GUS) expression, and subcellular localization assays indicated that OsCKX3 was highly expressed in the lamina joint, and OsCKX3-GFP fusion protein localized to the endoplasmic reticulum (ER). The enzyme assays using recombinant protein OsCKX3 revealed that OsCKX3 prefers trans-zeatin (tZ) and isopentenyladenine (iP). Consistently, tZ and iP levels increased in the osckx3 mutants but decreased in the OsCKX3 overexpression lines. Interestingly, agronomic trait analysis of the rice grown in the paddy field indicated that osckx3 displayed a smaller leaf angle and enhanced primary branch number, grain size, 1000-grain weight, and flag leaf size. Collectively, our results revealed that enhancing cytokinin levels in the lamina joint by disrupting OsCKX3 negatively regulates leaf angle, highlighting that the cytokinin pathway can be engineered to reduce leaf angle in rice and possibly in other cereals."
Authors: Zhifei Li, Ying Pi, Changsheng Zhai, Dong Xu, Wenyao Ma, Hong Chen, Yi Li and Han Wu.
Plant Cell Reports (2022)
Key message: Tomato DWARF14 regulates the development of roots, shoot branches and leaves, and also plays a role in photosynthetic pigment accumulation and photosynthetic capacity.
Abstract: "Strigolactones (SLs) are a novel class of plant hormones. DWARF14 (D14) is the only SL receptor identified to date, but it is not functionally analyzed in tomato (Solanum lycopersicum). In the present study, we identified the potential SL receptor in tomato by bioinformatic analysis, which was designated as SlD14. SlD14 was expressed in roots, stems, flowers and developing fruits, with the highest expression level in leaves. sld14 mutant plants produced by the CRISPR/Cas9 system displayed reduced plant height and root biomass, increased shoot branching and altered leaf shape comparing with WT plants. The cytokinin biosynthetic gene ISOPENTENYLTRANSFERASE 3 (SlIPT3), auxin biosynthetic genes FLOOZY (SlFZY) and TRYPTOPHAN AMINOTRANSFERASE RELATED 1 (SlTAR1) and several auxin transport genes SlPINs, which are involved in branch formation, showed higher expression levels in the sld14 plant stem. In addition, sld14 plants exhibited light-green leaves, reduced chlorophyll and carotenoid contents, abnormal chloroplast structure and reduced photosynthetic capacity. Transcriptomic analysis showed that the transcript levels of six chlorophyll biosynthetic genes, three carotenoid biosynthetic genes and numerous chlorophyll a/b-binding protein genes were decreased in sld14 plants. These results suggest that tomato SL receptor gene SlD14 not only regulates the development of roots, shoot branches and leaves, but also plays a role in regulating photosynthetic pigment accumulation and photosynthetic capacity."
Authors: Bruno Silvestre Lira, Maria José Oliveira, Lumi Shiose, Mateus Henrique Vicente, Gabriel Ponciano Carvalho Souza, Eny Iochevet Segal Floh, Eduardo Purgatto, Fabio Tebaldi Silveira Nogueira, Luciano Freschi and Magdalena Rossi.
Plant Molecular Biology (2022)
Key message: SlBBX28 is a positive regulator of auxin metabolism and signaling, affecting plant growth and flower number in tomato
Abstract: "B-box domain-containing proteins (BBXs) comprise a family of transcription factors that regulate several processes, such as photomorphogenesis, flowering, and stress responses. For this reason, attention is being directed toward the functional characterization of these proteins, although knowledge in species other than Arabidopsis thaliana remains scarce. Particularly in the tomato, Solanum lycopersicum, only three out of 31 SlBBX proteins have been functionally characterized to date. To deepen the understanding of the role of these proteins in tomato plant development and yield, SlBBX28, a light-responsive gene, was constitutively silenced, resulting in plants with smaller leaves and fewer flowers per inflorescence. Moreover, SlBBX28 knockdown reduced hypocotyl elongation in darkness-grown tomato. Analyses of auxin content and responsiveness revealed that SlBBX28 promotes auxin-mediated responses. Altogether, the data revealed that SlBBX28 promotes auxin production and signaling, ultimately leading to proper hypocotyl elongation, leaf expansion, and inflorescence development, which are crucial traits determining tomato yield.
Authors: Kyungyoon Kim, Bae Young Choi, Joohyun Kang, Donghwan Shim, Enrico Martinoia and Youngsook Lee.
Physiologia Plantarum (2022)
Abstract: "Abscisic acid (ABA) is a phytohormone that mediates stress responses and regulates plant development. Several ATP-binding cassette (ABC) transporters in the G subfamily of ABC (ABCG) proteins have been reported to transport ABA. We investigated whether there are any other ABCG proteins that mediate plant developmental processes regulated by ABA in Arabidopsis (Arabidopsis thaliana). The ABCG27 gene was upregulated in response to exogenous ABA treatment. The abcg27 knockout mutant exhibited two developmental defects: epinastic leaves and abnormally long pistils, which reduced fertility and silique length. ABCG27 expression was induced 3-fold when flower buds were exposed to exogenous ABA, and the promoter of ABCG27 had two ABA-responsive elements. ABA content in the pistil and true leaves were increased in the abcg27 knockout mutant. Detached abcg27 pistils exposed to exogenous ABA grew longer than those of the wild-type control. ABCG27 fused to GFP localized to the plasma membrane when expressed in Arabidopsis mesophyll protoplasts. A transcriptome analysis of the pistils and true leaves of the wild type and abcg27 knockout mutant revealed that the expression of organ development-related genes changed in the knockout mutant. In particular, the expression of trans-acting small interference (ta-si) RNA processing enzyme genes, which regulate flower and leaf development, was low in the knockout mutant. Together, these results suggest that ABCG27 most likely function as an ABA transporter at the plasma membrane, modulating ABA levels and thereby regulating the development of the pistils and leaves under normal, non-stressed conditions."
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Authors: Qingqing Wang, Marco Marconi, Chunmei Guan, Krzysztof Wabnik and Yuling Jiao.
PNAS (2022)
Significance: "Flattened leaf blade formation is a key adaption of plants to the environment, but its developmental regulation remains to be resolved. Classical microsurgery experiments suggest that a mobile signal, known as the Sussex signal, in the shoot apex is required for flattened leaf formation. A recent study found that polar auxin transport contributes to the Sussex signal, but how microsurgeries interact with polarity genes remains elusive. Here, we combine live-imaging and computer model simulations to show that an oval-shaped auxin response in inner cells of leaf primordium is essential for the formation of bipolar SlLAM1 expression domain, which establishes initial bilateral leaf primordia. Microsurgeries lead to an axisymmetric domain shape and can interfere with other polarity factors.
Abstract: "The flattened leaf form is an important adaptation for efficient photosynthesis, and the developmental process of flattened leaves has been intensively studied. Classic microsurgery studies in potato and tomato suggest that the shoot apical meristem (SAM) communicates with the leaf primordia to promote leaf blade formation. More recently, it was found that polar auxin transport (PAT) could mediate this communication. However, it is unclear how the expression of leaf patterning genes is tailored by PAT routes originating from SAM. By combining experimental observations and computer model simulations, we show that microsurgical incisions and local inhibition of PAT in tomato interfere with auxin transport toward the leaf margins, reducing auxin response levels and altering the leaf blade shape. Importantly, oval auxin responses result in the bipolar expression of SlLAM1 that determines leaf blade formation. Furthermore, wounding caused by incisions promotes degradation of SlREV, a known regulator of leaf polarity. Additionally, computer simulations suggest that local auxin biosynthesis in early leaf primordia could remove necessity for external auxin supply originating from SAM, potentially explaining differences between species. Together, our findings establish how PAT near emerging leaf primordia determines spatial auxin patterning and refines SlLAM1 expression in the leaf margins to guide leaf flattening."
Authors: Tom Rankenberg, Hans van Veen, Mastoureh Sedaghatmehr, Che-Yang Liao, Muthanna Biddanda Devaiah, Salma Balazadeh and Rashmi Sasidharan.
bioRxiv (2022)
Abstract: "The volatile phytohormone ethylene is a major regulator of plant adaptive responses to flooding. In flooded plant tissues, it quickly increases to high concentrations due to its low solubility and diffusion rates in water. The passive, quick and consistent accumulation of ethylene in submerged plant tissues makes it a reliable cue for plants to trigger flood-acclimative responses. However, persistent ethylene accumulation can also have negative effects, notably accelerated leaf senescence. Ethylene is a well-established positive regulator of senescence which is a natural element of plant ageing. However stress-induced senescence hampers the photosynthetic capacity and stress recovery of plants. In submerged Arabidopsis shoots, senescence follows a strict age-dependent pattern starting with the older leaves. Although mechanisms underlying ethylene-mediated senescence have been uncovered, it is unclear how submerged plants avoid an indiscriminate breakdown of leaves despite high systemic accumulation of ethylene. Here we demonstrate in Arabidopsis plants that even though submergence triggers a leaf-age independent activation of ethylene signaling via EIN3, senescence was initiated only in the old leaves. This EIN3 stabilization also led to the overall transcript and protein accumulation of the senescence-promoting transcription factor ORESARA1 (ORE1). ORE1 protein accumulated in both old and young leaves during submergence. However, leaf age-dependent senescence could be explained by ORE1 activation via phosphorylation only in old leaves. Our results unravel a mechanism by which plants regulate the speed and pattern of senescence during environmental stresses like flooding. Such an age-dependent phosphorylation of ORE1 ensures that older expendable leaves are dismantled first, thus prolonging the life of younger leaves and meristematic tissues vital to whole plant survival."
Authors: Yanliang Guo, Jingyi Zhu, Jiahe Liu, Yuxing Xue, Jingjing Chang, Yong Zhang, Golam Jalal Ahammed, Chunhua Wei, Jianxiang Ma, Pingfang Li, Xian Zhang and Hao Li.
Plant, Cell & Environment (2023)
Abstract: "Precocious leaf senescence can reduce crop yield and quality by limiting growth stage. Melatonin has been shown to delay leaf senescence; however, the underlying mechanism remains obscure. Here, we show that melatonin offsets abscisic acid (ABA) to protect photosystem II and delay the senescence of attached old leaves under the light. Melatonin induced H2O2 accumulation, accompanied by an upregulation of melon respiratory burst oxidase homolog D (CmRBOHD) under ABA-induced stress. Both melatonin and H2O2 induced the accumulation of cytoplasmic free Ca2+ ([Ca2+]cyt) in response to ABA, while blocking of Ca2+ influx channels attenuated melatonin- and H2O2-induced ABA tolerance. CmRBOHD overexpression induced [Ca2+]cyt accumulation and delayed leaf senescence, whereas, deletion of Arabidopsis AtRBOHD, a homologous gene of CmRBOHD, compromised the melatonin-induced [Ca2+]cyt accumulation and delay of leaf senescence in Arabidopsis under ABA stress. Furthermore, melatonin, H2O2 and Ca2+ attenuated ABA-induced K+ efflux and subsequent cell death. CmRBOHD overexpression and AtRBOHD deletion alleviated and aggravated the ABA-induced K+ efflux, respectively. Taken together, our study unveils a new mechanism by which melatonin offsets ABA action to delay leaf senescence via RBOHD-dependent H2O2 production that triggers [Ca2+]cyt accumulation and subsequently inhibits K+ efflux and delays cell death/leaf senescence in response to ABA."
Authors: Shengdong Li, Kun Xing, Ghulam Qanmber, Guoquan Chen, Le Liu, Mengzhen Guo, Yan Hou, Lili Lu, Lingbo Qu, Zhao Liu and Zuoren Yang.
Plant Molecular Biology (2022)
Key message: We proposed a working model of BR to promote leaf size through cell expansion. In the BR signaling pathway, GhBES1 affects cotton leaf size by binding to and activating the expression of the E-box element in the GhEXO2 promoter region.
Abstract: "Brassinosteroid (BR) is an essential phytohormone that controls plant growth. However, the mechanisms of BR regulation of leaf size remain to be determined. Here, we found that the BR deficient cotton mutant pagoda1 (pag1) had a smaller leaf size than wild-type CRI24. The expression of EXORDIUM (GhEXO2) gene, was significantly downregulated in pag1. Silencing of BRI1-EMS-SUPPRESSOR 1 (GhBES1), inhibited leaf cell expansion and reduced leaf size. Overexpression of GhBES1.4 promoted leaf cell expansion and enlarged leaf size. Expression analysis showed GhEXO2 expression positively correlated with GhBES1 expression. In plants, altered expression of GhEXO2 promoted leaf cell expansion affecting leaf size. Furthermore, GhBES1.4 specifically binds to the E-box elements in the GhEXO2 promoter, inducing its expression. RNA-seq data revealed many down-regulated genes related to cell expansion in GhEXO2 silenced plants. In summary, we discovered a novel mechanism of BR regulation of leaf size through GhBES1 directly activating the expression of GhEXO2."
Author: Leah R. Band (2022)
PLOS Biology (2022)
Excerpts: "It is well established that the hormone auxin regulates vein patterning. The seminal studies of Sachs [1] showed that auxin application induces the formation of new veins; this observation led to the well-known “Canalisation hypothesis” that proposes that movement of an auxin-dependent signal through cells increases the cell’s capacity for auxin transport [1]."
"However, until now, the mechanistic basis of vein pattern formation remained elusive, given plants inhibited in both carrier-mediated auxin transport and auxin signalling still form some vein patterns [4]. In their new study published in PLOS Biology, Linh and Scarpella investigated whether diffusion through plasmodesmata plays a role in vein patterning, revealing this to be an essential component of vein patterning [5].
"In summary, Linh and Scarpella [5] elucidate a key mechanistic component of Sach’s Canalisation hypothesis. Their elegant study demonstrates that regulation of plasmodesmata is essential for vein patterning. They conclude that vein patterning occurs through the co-ordinated action of auxin signalling, polar transport, and diffusion of an auxin signal through plasmodesmata, 3 processes that are all regulated by GNOM."
Authors: Xiaojia Zhang, Baolin Zhao, Yibo Sun and Yulong Feng.
Frontiers in Plant Science (2022)
Abstract: "Horticultural plants such as vegetables, fruits, and ornamental plants are crucial to human life and socioeconomic development. Gibberellins (GAs), a class of diterpenoid compounds, control numerous developmental processes of plants. The roles of GAs in regulating growth and development of horticultural plants, and in regulating significant progress have been clarified. These findings have significant implications for promoting the quality and quantity of the products of horticultural plants. Here we review recent progress in determining the roles of GAs (including biosynthesis and signaling) in regulating plant stature, axillary meristem outgrowth, compound leaf development, flowering time, and parthenocarpy. These findings will provide a solid foundation for further improving the quality and quantity of horticultural plants products."
Authors: Jiyue Qiao, Yanjun Zhang, ShaqiLa Han, Senqiu Chang, Zhenyu Gao, Yanhua Qi and Qian Qian.
Frontiers in Plant Science (2022)
Abstract: "Leaf inclination is a vital agronomic trait and is important for plant architecture that affects photosynthetic efficiency and grain yield. To understand the molecular mechanisms underlying regulation of leaf inclination, we constructed an auxin response factor (arf) rice mutant—osarf4—showing increased leaf inclination using CRISPR/Cas9 gene editing technology. OsARF4 encodes a nuclear protein that is expressed in the lamina joint (LJ) at different developmental stages in rice. Histological analysis indicated that an increase in cell differentiation on the adaxial side resulted in increased leaf inclination in the osarf4 mutants; however, OsARF4-overexpressing lines showed a decrease in leaf inclination, resulting in erect leaves. Additionally, a decrease in the content and distribution of indole-3-acetic acid (IAA) in osarf4 mutant led to a greater leaf inclination, whereas the OsARF4-overexpressing lines showed the opposite phenotype with increased IAA content. RNA-sequencing analysis revealed that the expression of genes related to brassinosteroid (BR) biosynthesis and response was different in the mutants and overexpressing lines, suggesting that OsARF4 participates in the BR signaling pathway. Moreover, BR sensitivity assay revealed that OsARF4-overexpressing lines were more sensitive to exogenous BR treatment than the mutants. In conclusion, OsARF4, a transcription factor in auxin signaling, participates in leaf inclination regulation and links auxin and BR signaling pathways. Our results provide a novel insight into l leaf inclination regulation, and have significant implications for improving rice architecture and grain yield."
Authors: Hui Wang, Xue Li, Tezera Wolabu, Ziyao Wang, Ye Liu, Dimiru Tadesse, Naichong Chen, Aijiao Xu, Xiaojing Bi, Yunwei Zhang, Jianghua Chen and Million Tadege.
The Plant Cell (2022)
Abstract: "The plant-specific family of WUSCHEL (WUS)-related homeobox (WOX) transcription factors is key regulators of embryogenesis, meristem maintenance, and lateral organ development in flowering plants. The modern/WUS clade transcriptional repressor STENOFOLIA/LAMINA1(LAM1), and the intermediate/WOX9 clade transcriptional activator MtWOX9/NsWOX9 antagonistically regulate leaf blade expansion, but the molecular mechanism is unknown. Using transcriptome profiling and biochemical methods, we determined that NsCKX3 is the common target of LAM1 and NsWOX9 in Nicotiana sylvestris. LAM1 and NsWOX9 directly recognize and bind to the same cis-elements in the NsCKX3 promoter to repress and activate its expression, respectively, thus controlling the levels of active cytokinins in vivo. Disruption of NsCKX3 in the lam1 background yielded a phenotype similar to the knockdown of NsWOX9 in lam1, while overexpressing NsCKX3 resulted in narrower and shorter lam1 leaf blades reminiscent of NsWOX9 overexpression in the lam1 mutant. Moreover, we established that LAM1 physically interacts with NsWOX9, and this interaction is required to regulate NsCKX3 transcription. Taken together, our results indicate that repressor and activator WOX members oppositely regulate a common downstream target to function in leaf blade outgrowth, offering a novel insight into the role of local cytokinins in balancing cell proliferation and differentiation during lateral organ development."
Authors: Xiaokun Wang, Xianglan Wang, Shilei Sun, Xiaoyu Tu, Kande Lin, Lei Qin, Xingyun Wang, Gang Li, Silin Zhong and Pinghua Li.
Plant Physiology (2022)
Abstract: "Leaf angle is an important agronomic trait determining maize (Zea mays) planting density and light penetration into the canopy and contributes to the yield gain in modern maize hybrids. However, little is known about the molecular mechanisms underlying leaf angle beyond the ZmLG1 (liguleless1) and ZmLG2 (Liguleless2) genes. In this study, we found that the transcription factor (TF) ZmBEH1 (BZR1/BES1 homolog gene 1) is targeted by ZmLG2 and regulates leaf angle formation by influencing sclerenchyma cell layers on the adaxial side. ZmBEH1 interacted with the TF ZmBZR1 (Brassinazole Resistant 1), whose gene expression was also directly activated by ZmLG2. Both ZmBEH1 and ZmBZR1 are bound to the promoter of ZmSCL28 (SCARECROW-LIKE 28), a third TF that influences leaf angle. Our study demonstrates regulatory modules controlling leaf angle and provides gene editing targets for creating optimal maize architecture suitable for dense planting."
Authors: Xiaomeng Zhang, Wei Ma, Mengyang Liu, Xing Li, Jingrui Li, Yin Lu, Guanghuan Li, Shu Zhang, Daling Feng, Yanhua Wang, Hao Liang, Shuangxia Luo, Na Li, Aixia Gu, Shuxin Xuan, Xueping Chen, Shuxing Shen and Jianjun Zhao.
PNAS (2022)
Significance: Heading is a pivotal agronomic trait for Chinese cabbage, cabbage, and lettuce. The heading leaves serve as nutrient storage organs, which contribute to good quality and the economic value of leafy heads. However, the genetic basis underlying the head formation remains largely unexplored. Here, we constructed an F2 population with the segregation in the heading phenotype to identify the BrOPS gene that controls leaf curvature in a brassinosteroid-dependent manner. BrOPS interacts with BrBIN2 to modulate the phosphorylation of BrBES1 that negatively regulates the expression of leaf polarity transcription factor BrAS1, thereby influencing leaf curvature and heading shape in Chinese cabbage. Our data provide novel insights into leaf development and add values to future breeding of different heading types of vegetables.
Abstract: "Heading is one of the most important agronomic traits for Chinese cabbage crops. During the heading stage, leaf axial growth is an essential process. In the past, most genes predicted to be involved in the heading process have been based on leaf development studies in Arabidopsis. No genes that control leaf axial growth have been mapped and cloned via forward genetics in Chinese cabbage. In this study, we characterize the inward curling mutant ic1 in Brassica rapa ssp. pekinensis and identify a mutation in the OCTOPUS (BrOPS) gene by map-based cloning. OPS is involved in phloem differentiation in Arabidopsis, a functionalization of regulating leaf curvature that is differentiated in Chinese cabbage. In the presence of brassinosteroid (BR) at the early heading stage in ic1, the mutation of BrOPS fails to sequester brassinosteroid insensitive 2 (BrBIN2) from the nucleus, allowing BrBIN2 to phosphorylate and inactivate BrBES1, which in turn relieves the repression of BrAS1 and results in leaf inward curving. Taken together, the results of our findings indicate that BrOPS positively regulates BR signaling by antagonizing BrBIN2 to promote leaf epinastic growth at the early heading stage in Chinese cabbage."
Authors: Yue Jia, Pei Yu, Wei Shao, Guanghui An, Jiongjiong Chen, Changchun Yu and Hanhui Kuang.
Journal of Experimental Botany (2022)
Abstract: "Lettuce (Lactuca sativa) is one of the most popular vegetables worldwide. Diverse leaf shapes, including wavy leaves, are important traits for lettuce. We dissected the genetics of wavy leaves using an F2 segregating population of lettuce. A major QTL controlling wavy leaves was identified. The candidate region contains the LsKN1 gene, which was previously shown to be indispensable for leafy heads in lettuce. Complementation test and knockout experiments verified the function of LsKN1 on wavy leaves. The LsKN1 allele, which has the insertion of a transposon and controls leafy head in a previous population, promotes wavy leaves in the current population. Occasional transposition of the CACTA transposon from the LsKN1 gene compromised its function on wavy leaves. High expression of the LsKN1 gene upregulates several key genes associated with cytokinin (CK) to increase its contents in leaves. In contrast, high expression of the LsKN1 gene downregulates the expression of genes in the gibberellin (GA) biosynthesis pathway to decrease GA contents in leaves. Application of CK on leaves increased wavy phenotype, while application of GA dramatically flattened the leaves. We conclude that high expression of the LsKN1 gene increases CK contents but decreases GA contents in leaves, switches determinate cells to indeterminate, and consequently leads to wavy leaves."
Authors: Shengnan Huang, Yue Gao, Meihui Xue, Junjie Xu, Ruiqi Liao, Shayu Shang, Xiaofei Yang, Yonghui Zhao, Chengyu Li, Zhiyong Liu and Hui Feng.
Theoretical and Applied Genetics (2022)
Key message: The role of BrKAO2 in leafy head formation was confirmed by using two allelic Chinese cabbage mutants.
Abstract: "Chinese cabbage yield and quality are determined by leafy head formation. Cloning and characterising the key genes regulating leafy head formation are essential for its varietal improvement. We used an EMS-mutagenised population of the heading type ‘FT’ Chinese cabbage line and identified two allelic non-heading mutants, i.e. nhm3-1 and nhm3-2. Genetic analysis showed that the mutant trait was controlled by a single recessive gene. MutMap and Kompetitive Allele Specific PCR genotyping revealed that BraA05g012440.3C was the candidate gene, which encodes ent-kaurenoic acid oxidase 2 in gibberellin (GA) biosynthetic pathway. It was named BrKAO2. Two non-synonymous mutations in the second BrKAO2 exon, respectively, accounted for the mutant phenotypes of nhm3-1 and nhm3-2. BrKAO2 was expressed during all leaf development stages, and there were no significant differences between the wild type and mutants in terms of BrKAO2 expression. The mutant phenotypes were restored to the wild type via exogenous GA3 application. RNA-Seq was performed on wild-type ‘FT’, nhm3-1, and nhm3-1 + GA3 rosette leaves, and several key genes involved in GA biosynthesis, signal transduction, and leafy head development were identified. These findings indicate that BrKAO2 is responsible for the leafy head formation in nhm3 mutants."
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