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Authors: Fei Jin, Liping Zhu, Liyong Hou, Hongbin Li, Ling Li and Guanghui Xiao.
Plant Physiology (2024)
One-sentence summary: Two auxin/indole-3-acetic acid proteins interact with distinct auxin response factors and antagonistically control cotton fiber elongation and initiation.
Abstract: "Auxin, a pivotal regulator of diverse plant growth processes, remains central to development. The auxin-responsive genes auxin/indole-3-acetic acids (AUX/IAAs) are indispensable for auxin signal transduction, which is achieved through intricate interactions with auxin response factors (ARFs). Despite this, the potential of AUX/IAAs to govern the development of the most fundamental biological unit, the single cell, remains unclear. In this study, we harnessed cotton (Gossypium hirsutum) fiber, a classic model for plant single-cell investigation, to determine the complexities of AUX/IAAs. Our research identified two pivotal AUX/IAAs, auxin resistant 2 (GhAXR2) and short hypocotyl 2 (GhSHY2), which exhibit opposite control over fiber development. Notably, suppressing GhAXR2 reduced fiber elongation, while silencing GhSHY2 fostered enhanced fiber elongation. Investigating the mechanistic intricacies, we identified specific interactions between GhAXR2 and GhSHY2 with distinct ARFs. GhAXR2’s interaction with GhARF6-1 and GhARF23-2 promoted fiber cell development through direct binding to the AuxRE cis-element in the constitutive triple response 1 (GhCTR1) promoter, resulting in transcriptional inhibition. In contrast, the interaction of GhSHY2 with GhARF7-1 and GhARF19-1 exerted a negative regulatory effect, inhibiting fiber cell growth by activating the transcription of xyloglucan endotransglucosylase/hydrolase 9 (GhXTH9) and cinnamate-4-hydroxylase (GhC4H). Thus, our study reveals the intricate regulatory networks surrounding GhAXR2 and GhSHY2, elucidating the complex interplay of multiple ARFs in AUX/IAA-mediated fiber cell growth. This work enhances our understanding of single-cell development and has potential implications for advancing plant growth strategies and agricultural enhancements."
Authors: Keming Luo, Shuai Liu, Xiaokang Fu, Xuelian Du, Jian Hu, Lianjia Luo, Changjian Fa, Rongling Wu, Laigeng Li and Changzheng Xu.
Research Square (2023)
Abstract: "Auxin, as a vital phytohormone, is enriched in the vascular cambium, playing a crucial role in regulating wood formation in trees. Despite its significance, the molecular mechanisms underlying the influence of auxin on wood development remain elusive. In this study, we report a transcription factor, PLETHORA 5 (PLT5), whose expression was specifically activated by auxin signalling in the vascular cambium. PLT5 was found to regulate cell expansion and lignification of fibres in poplar. Genetic experiments confirmed the noncell-autonomous regulation of auxin signalling from the vascular cambium and revealed the necessity of PLT5 protein mobility to mediate this process. Remarkably, PLT5 proteins specifically inhibit the initiation of fibre cell wall thickening by directly repressing SND1 genes. This study unveils a sophisticated model wherein the auxin-PLT5 signalling cascade intricately regulates wood fibre development in poplar by fine-tuning the thickening of fibre cell walls."
Authors: Qingwei Song, Wanting Gao, Chuanhui Du, Wenjie Sun, Jin Wang and Kaijing Zuo.
Plant Biotechnology Journal (2023)
Abstract: "Ethylene plays an essential role in the development of cotton fibres. Ethylene biosynthesis in plants is elaborately regulated by the activities of key enzymes, 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS); however, the potential mechanism of post-translational modification of ACO and ACS to control ethylene synthesis in cotton fibres remains unclear. Here, we identify an E3 ubiquitin ligase, GhXB38D, that regulates ethylene biosynthesis during fibre elongation in cotton. GhXB38D gene is highly expressed in cotton fibres during the rapid elongation stage. Suppressing GhXB38D expression in cotton significantly enhanced fibre elongation and length, accompanied by the up-regulation of genes associated with ethylene signalling and fibre elongation. We demonstrated that GhXB38D interacts with the ethylene biosynthesis enzymes GhACS4 and GhACO1 in elongating fibres and specifically mediates their ubiquitination and degradation. The inhibition of GhXB38D gene expression increased the stability of GhACS4 and GhACO1 proteins in cotton fibres and ovules, resulting in an elevated concentration of ethylene. Our findings highlight the role of GhXB38D as a regulator of ethylene synthesis by ubiquitinating ACS4 and ACO1 proteins and modulating their stability. GhXB38D acts as a negative regulator of fibre elongation and serves as a potential target for enhancing cotton fibre yield and quality through gene editing strategy."
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: Jianyan Zeng, Dan Yao, Ming Luo, Lingli Ding, Yi Wang, Xingying Yan, Shu'e Ye, Chuannan Wang, Yiping Wu, Jingyi Zhang, Yaohua Li, Lingfang Ran, Yonglu Dai, Yang Chen, Fanlong Wang, Hanyan Lai, Nian Liu, Nianjuan Fang, Yan Pei and Yuehua Xiao.
The Crop Journal (2023)
Abstract: "Cotton fiber is a raw material for the global textile industry and fiber quality is essential to its industrial application. Carotenoids are plant secondary metabolites that may serve as dietary components, regulate light harvesting, and scavenge reactive oxygen species. Although carotenoids accumulate predominantly in rapidly elongating cotton fibers, their roles in cotton fiber development remain poorly understood. In this study, a fiber-specific promoter proSCFP was applied to drive the expression of GhOR1Del, a positive regulator of carotenoid accumulation, to upregulate the carotenoid level in cotton fiber in planta. Fiber length, strength, and fineness were increased in proSCFP:GhOR1Del transgenic cotton and abscisic acid (ABA) and ethylene contents were increased in elongating fibers. The ABA downstream regulator GhbZIP27a stimulated the expression of the ethylene synthase gene GhACO3 by binding to its promoter, suggesting that ABA promoted fiber elongation by increasing ethylene production. These findings suggest the involvement of carotenoids and ABA signaling in promoting cotton fiber elongation and provide a strategy for improving cotton fiber quality."
Authors: Samina Yousaf, Tanzeela Rehman, Bushra Tabassum, Faheem Aftab and Uzma Qaisar.
Scientific Reports (2023)
Abstract: "A class of proteins, 1-aminocyclopropane-1-carboxylate oxidase (ACO), is required in the final step of production of ethylene from its immediate precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Despite the crucial and regulatory role of ACO gene family in the fiber development, it has not been thoroughly analyzed and annotated in G. barbadense genome. In the present study, we have identified and characterized all isoforms of ACO gene family from genomes of Gossypium arboreum, G. barbadense, G. hirsutum and G. raimondii. Phylogenetic analysis classified all ACO proteins into six distinct groups on the basis of maximum likelihood. Gene locus analysis and circos plots indicated the distribution and relationship of these genes in cotton genomes. Transcriptional profiling of ACO isoforms in G. arboreum, G. barbadense and G. hirsutum fiber development exhibited the highest expression in G. barbadense during early fiber elongation. Moreover, the accumulation of ACC was found highest in developing fibers of G. barbadense in comparison with other cotton species. ACO expression and ACC accumulation correlated with the fiber length in cotton species. Addition of ACC to the ovule cultures of G. barbadense significantly increased fiber elongation while ethylene inhibitors hindered fiber elongation. These findings will be helpful in dissecting the role of ACOs in cotton fiber development and pave a way towards genetic manipulations for fiber quality improvement."
Authors: Jing Xi, Jianyan Zeng, Xingxian Fu, Liuqin Zhang, Gailing Li, Baoxia Li, Xingying Yan, Qingqing Chu, Yuehua Xiao, Yan Pei and Mi Zhang.
Journal of Experimental Botany (2023)
Abstract: "PIN-FORMED- (PIN) mediated polar auxin transport plays a predominant role in most auxin-triggered organogenesis in plants. Global control of PIN polarity at the plasma membrane contributes to the essential establishment of auxin maxima in most multicellular tissues. However, establishment of auxin maxima in single cells is poorly understood. Cotton fibers, derived from ovule epidermal cells by auxin-triggered cell protrusion, provide an ideal model to explore the underlying mechanism. Here, we report that cell-specific degradation of GhPIN3a, which guides the establishment of the auxin gradient in cotton ovule epidermal cells, is associated with the preferential expression of GhROP6 GTPase in fiber cells. In turn, GhROP6 reduces GhPIN3a abundance at the plasma membrane and facilitates intracellular proteolysis of GhPIN3a. Overexpression and activation of GhROP6 promote cell elongation, resulting in a substantial improvement in cotton fiber length."
Author: Marco Bürger
The Plant Cell (2022)
Excerpts: "Two important contributors to fiber development are cell elongation and secondary wall thickness. In a new publication, Yuzhou Zhang, Zailong Tian, and colleagues (Zhang et al., 2022) show that gibberellins activate SL biosynthesis to enhance cell wall thickness and the elongation of fiber cells in cotton."
"Zhang and co-workers therefore established that SLs have a dual role in cotton: They not only promote fiber cell elongation, but also enhance secondary cell wall thickness."
"GA, therefore, through GRF4, directly activates the expression of the SL biosynthesis gene D27 to trigger the SL-mediated increase in fiber cell elongation and cell wall thickness (see Figure)."
Authors: Jianyan Zeng, Xingying Yan, Wenqin Bai, Mi Zhang, Yang Chen, Xianbi Li, Lei Hou, Juan Zhao, Xiaoyan Ding, Ruochen Liu, Fanlong Wang, Hui Ren, Jingyi Zhang, Bo Ding, Haoru Liu, Yuehua Xiao and Yan Pei.
Journal of Experimental Botany (2022)
Abstract: "Cytokinin is considered to be an important driver of seed yield. To increase the yield of cotton while avoiding the negative consequences caused by constitutive overproduction of cytokinin, we carpel-specifically downregulated cytokinin oxidase/dehydrogenase (CKX), a key negative regulator of cytokinin levels, in transgenic cotton. The carpel-specific downregulation of CKXs significantly enhanced cytokinin levels in the carpels. The elevated cytokinin promoted the expression of carpel- and ovule-development associated genes, GhSTK2, GhAG1, and GhSHP, boosting ovule formation and thus producing more seeds in the ovary. Field experiments showed that the carpel-specific increase of cytokinin significantly increased both seed yield and fiber yield of cotton, without resulting in detrimental phenotypes. Our study details the regulatory mechanism of cytokinin signaling for seed development, and provides an effective and feasible strategy for the yield improvement of seed crops."
Authors: Zemin Shi, Xia Chen, Huidan Xue, Tingting Jia, Funing Meng, Yunfei Liu, Xiaomin Luo, Guanghui Xiao and Shengwei Zhu.
The Plant Journal (2022)
Abstract: "The Brassinazole-Resistant (BZR) transcription factor is a core component of brassinosteroid (BR) signaling and involved in the development of many plant species. BR is essential for the initiation and elongation of cotton fibers. However, the mechanism of BR-regulating fiber development and the function of BZR is poorly understood in cotton. Here, we identified a BZR family transcription factor protein referred to as GhBZR3 in cotton. Overexpression of GhBZR3 in Arabidopsis caused shorter root hair length, hypocotyl length, and hypocotyl cell length, indicating that GhBZR3 negatively regulates cell elongation. Pathway enrichment analysis from VIGS-GhBZR3 cotton plants found that fatty acid metabolism and degradation might be the regulatory pathway that is primarily controlled by GhBZR3. Silencing GhBZR3 expression in cotton resulted in taller plant height as well as longer fibers. The very-long-chain fatty acid (VLCFA) content was also significantly increased in silenced GhBZR3 plants compared to wild-type. The GhKCS13 promoter, a key gene for VLCFA biosynthesis, contains two GhBZR3 binding sites. The results of yeast one-hybrid, electrophoretic mobility shift, and luciferase assays revealed that GhBZR3 directly interacted with the GhKCS13 promoter to suppress gene expression. Taken together, these results indicated that GhBZR3 negatively regulates cotton fiber development by reducing VLCFA biosynthesis. This study not only deepens our understanding of GhBZR3 function in cotton fiber development but also highlights the potential of improving cotton fiber length and plant growth using GhBZR3 and its related genes in future cotton breeding programs."
Authors: Masood Jan, Zhixin Liu, Chenxi Guo and Xuwu Sun.
International Journal of Molecular Sciences (2022)
Abstract: "Cotton (Gossypium spp.) is an economically important natural fiber crop. The quality of cotton fiber has a substantial effect on the quality of cotton textiles. The identification of cotton fiber development-related genes and exploration of their biological functions will not only enhance our understanding of the elongation and developmental mechanisms of cotton fibers but also provide insights that could aid the cultivation of new cotton varieties with improved fiber quality. Cotton fibers are single cells that have been differentiated from the ovule epidermis and serve as a model system for research on single-cell differentiation, growth, and fiber production. Genes and fiber formation mechanisms are examined in this review to shed new light on how important phytohormones, transcription factors, proteins, and genes linked to fiber development work together. Plant hormones, which occur in low quantities, play a critically important role in regulating cotton fiber development. Here, we review recent research that has greatly contributed to our understanding of the roles of different phytohormones in fiber development and regulation. We discuss the mechanisms by which phytohormones regulate the initiation and elongation of fiber cells in cotton, as well as the identification of genes involved in hormone biosynthetic and signaling pathways that regulate the initiation, elongation, and development of cotton fibers."
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Authors: Peng He, Liping Zhu, Xin Zhou, Xuan Fu, Yu Zhang, Peng Zhao, Bin Jiang, Huiqin Wang and Guanghui Xiao.
Developmental Cell (2024)
Editor's view: He et al. identified two signaling cascades, GhSLR1-GhZFP8-GhSDCP1- GhPIF3 and GhSLR1-GhBLH1-GhKCS12, which translate the gibberellins signal to regulate cotton fiber cell elongation. This finding can be potentially used in the field to improve cotton fiber quality.
Highlight: • Gibberellins promotes fiber cell elongation by degrading GhSLR1 • GhSLR1 interacts with two transcription factors, GhZFP8 and GhBLH1 • GhBLH1 activates the transcription of GhKCS12 and enhances VLCFA biosynthesis • GhZFP8 activates the expression of GhPIF3 by upregulating GhSDCP1 in cotton
Abstract: "The agricultural green revolution spectacularly enhanced crop yield through modification of gibberellin (GA) signaling. However, in cotton, the GA signaling cascades remain elusive, limiting our potential to cultivate new cotton varieties and improve yield and quality. Here, we identified that GA prominently stimulated fiber elongation through the degradation of DELLA protein GhSLR1, thereby disabling GhSLR1’s physical interaction with two transcription factors, GhZFP8 and GhBLH1. Subsequently, the resultant free GhBLH1 binds to GhKCS12 promoter and activates its expression to enhance VLCFAs biosynthesis. With a similar mechanism, the free GhZFP8 binds to GhSDCP1 promoter and activates its expression. As a result, GhSDCP1 upregulates the expression of GhPIF3 gene associated with plant cell elongation. Ultimately, the two parallel signaling cascades synergistically promote cotton fiber elongation. Our findings outline the mechanistic framework that translates the GA signal into fiber cell elongation, thereby offering a roadmap to improve cotton fiber quality and yield."
Authors: Fang Liu, Ting Wei, Qiaoling Wang, Guiming Li, Qian Meng, Li Huang, Xi Cheng, Xingying Yan, Yulin Hu, Fan Xu and Ming Luo.
Industrial Crops and Products (2023)
Highlights: • GhSMO2-2 played role in cotton fiber elongation. • GhSMO2-2 was regulated by BR signal and influenced sterol and sphingolipid contents.
Abstract: "Cotton fiber cell is an extremely elongated single cell and is regarded as an ideal material to study the growth and development of plant cell. Phytohormone brassinosteroids (BRs) play crucial roles in fiber cell development. However, its action mechanism in fiber growth is largely unknown. In this study, we identified a homologue of Arabidopsis SMO2–2 (Sterol C-4α Methyl Oxidase), GhSMO2–2, in upland cotton (Gossypium hirsutum L.), which predominantly expressed in fiber cell and peaked at the rapid elongation stage, and responded to BR signal. The GhBES1, a transcription factor in BR signaling could directly bind to the promoter of GhSMO2–2 and promoted its expression. Overexpression of GhSMO2–2 significantly promoted fiber cell elongation and phytosterol synthesis in cotton, and elevated some sphingolipid species that was important for fiber elongation. On the contrary, down-regulating GhSMO2–2 suppressed fiber elongation and blocked these chemicals accumulation. These results indicated that GhSMO2–2 is an important gene involved in fiber cell elongation, and is valuable for genetic engineering to improve fiber quality and yield. Taken together, our study revealed that BR regulated fiber cell elongation by influencing phytosterol and sphingolipid biosynthesis, the key components of membrane lipid raft and provided a new clue for further revealing the function and mechanism of phytosterols, sphingolipids, and BRs in plant cell development."
Authors: Yao Wang, Yang Li, Shao-Ping He, Shang-Wei Xu, Li Li, Yong Zheng and Xue-Bao Li.
The Plant Cell (2023)
Abstract: "Phytohormones play indispensable roles in plant growth and development. However, the molecular mechanisms underlying phytohormone-mediated regulation of fiber secondary cell wall (SCW) formation in cotton (Gossypium hirsutum) remain largely underexplored. Here, we provide mechanistic evidence for functional interplay between the AP2/ERF transcription factor GhERF108 and auxin response factors GhARF7-1 and GhARF7-2 in dictating the ethylene-auxin signaling crosstalk that regulates fiber SCW biosynthesis. Specifically, in vitro cotton ovule culture revealed that ethylene and auxin promote fiber SCW deposition. GhERF108 RNAi cotton displayed remarkably reduced cell wall thickness compared with controls. GhERF108 interacted with GhARF7-1 and GhARF7-2 to enhance the activation of the MYB transcription factor gene GhMYBL1 (MYB domain like protein 1) in fibers. GhARF7-1 and GhARF7-2 respond to auxin signals that promote fiber SCW thickening. GhMYBL1 RNAi and, GhARF7-1 and GhARF7-2 VIGS cotton displayed similar defects in fiber SCW formation as GhERF108 RNAi cotton. Moreover, the ethylene and auxin responses were reduced in GhMYBL1 RNAi plants. GhMYBL1 directly binds to the promoters of GhCesA4-1, GhCesA4-2, and GhCesA8-1 and activates their expression to promote cellulose biosynthesis, thereby boosting fiber SCW formation. Collectively, our findings demonstrate that the collaboration between GhERF108 and GhARF7-1 or GhARF7-2 establishes ethylene-auxin signaling crosstalk to activate GhMYBL1, ultimately leading to the activation of fiber SCW biosynthesis."
Authors: Yu Gu, Jie Zhang, Le Liu, Ghulam Qanmber, Zhao Liu, Kun Xing, Lili Lu, Li Liu, Shuya Ma, Fuguang Li and Zuoren Yang.
The Plant Journal (2023)
Abstract: "The steroidal hormone brassinosteroid (BR) has been shown to positively regulate cell expansion in plants. However, the specific mechanism by which BR controls this process has not been fully understood. In this study, RNA-seq and DAP-seq analysis of GhBES1.4 (a core transcription factor in BR signaling) were used to identify a cotton cell cycle-dependent kinase inhibitor called GhKRP6. The study found that GhKRP6 was significantly induced by the BR hormone, and that GhBES1.4 directly promoted the expression of GhKRP6 by binding to the CACGTG motif in its promoter region. GhKRP6-silenced cotton plants had smaller leaves with more cells and reduced cell size. Furthermore, endoreduplication was inhibited, which affected cell expansion and ultimately decreased fiber length and seed size in GhKRP6-silenced plants compared with the control. The KEGG enrichment results of control and VIGS-GhKRP6 plants revealed differential expression of genes related to cell wall biosynthesis, MAPK, and plant hormone transduction pathways – all of which are related to cell expansion. Additionally, some cyclin-dependent kinase (CDK) genes were up-regulated in the plants with silenced GhKRP6. Our study also found that GhKRP6 could interact directly with a cell cycle-dependent kinase called GhCDKG. Taken together, these results suggest that BR signaling influences cell expansion by directly modulating the expression of cell cycle-dependent kinase inhibitor GhKRP6 via GhBES1.4."
Authors: Liping Zhu, Huiqin Wang, Jiaojie Zhu, Xiaosi Wang, Bin Jiang, Liyong Hou and Guanghui Xiao.
Cell Reports (2023)
Editor's view: Zhu et al. demonstrate that BES1 binds the E-box of the CERP promoter, and CERP further binds the E-box of the EXPA3-1 promoter to activate corresponding gene transcription. The BES1-CERP-EXPA3-1 cascade is conserved in BR-mediated plant single- cell elongation.
Highlights • BR and GhBES1 positively regulate fiber cell elongation • GhBES1 activates the transcription of GhCERP via binding to E-box of GhCERP promoter • GhEXPA3-1 is a downstream target of GhCERP • BES1-CERP-EXPA3 might be a broad-spectrum pathway in BR-promoted cell elongation
Abstract: "Continuous plant growth is achieved by cell division and cell elongation. Brassinosteroids control cell elongation and differentiation throughout plant life. However, signaling cascades underlying BR-mediated cell elongation are unknown. In this study, we introduce cotton fiber, one of the most representative single-celled tissues, to decipher cell-specific BR signaling. We find that gain of function of GhBES1, a key transcriptional activator in BR signaling, enhances fiber elongation. The chromatin immunoprecipitation sequencing analysis identifies a cell-elongation-related protein, GhCERP, whose transcription is directly activated by GhBES1. GhCERP, a downstream target of GhBES1, transmits the GhBES1-mediated BR signaling to its target gene, GhEXPA3-1. Ultimately, GhEXPA3-1 promotes fiber cell elongation. In addition, inter-species functional analysis of the BR-mediated BES1-CERP-EXPA3 signaling cascade also promotes Arabidopsis root and hypocotyl growth. We propose that the BES1-CERP-EXPA3 module may be a broad-spectrum pathway that is universally exploited by diverse plant species to regulate BR-promoted cell elongation."
Authors: Zuoren Yang, Zhao Liu, Xiaoyang Ge, Lili Lu, Wenqiang Qin, Ghulam Qanmber, Le Liu, Zhi Wang and Fuguang Li.
The Plant Cell (2023)
Abstract: "Brassinosteroid (BR), a growth-promoting phytohormone, regulates many plant growth processes including cell development. However, the mechanism by which BR regulates fiber growth is poorly understood. Cotton (Gossypium hirsutum) fibers are an ideal single-cell model in which to study cell elongation due to their length. Here we report that BR controls cotton fiber elongation by modulating very-long-chain fatty acid (VLCFA) biosynthesis. BR deficiency reduces the expression of 3-ketoacyl-CoA synthases (GhKCSs), the rate-limiting enzymes involved in VLCFA biosynthesis, leading to lower saturated VLCFAs contents in pagoda1 (pag1) mutant fibers. In vitro ovule culture experiments show that BR acts upstream of VLCFAs. Silencing of BRI1-EMS-SUPPRESOR 1.4 (GhBES1.4), encoding a master transcription factor (TF) of the BR signaling pathway, significantly reduces fiber length, whereas GhBES1.4 over-expression produces longer fibers. GhBES1.4 regulates endogenous VLCFA contents and directly binds to BR RESPONSE ELEMENTS (BRREs) in the GhKCS10_At promoter region, which in turn regulates GhKCS10_At expression to increase endogenous VLCFA contents. GhKCS10_At overexpression promotes cotton fiber elongation, whereas GhKCS10_At silencing inhibits cotton fiber growth, supporting a positive regulatory role for GhKCS10_At in fiber elongation. Overall, these results uncover a mechanism of fiber elongation through crosstalk between BR and VLCFAs at the single-cell level."
Authors: Le Liu, Guoquan Chen, Shengdong Li, Yu Gu, Lili Lu, Ghulam Qanmber, Venugopal Mendu, Zhao Liu, Fuguang Li and Zuoren Yang.
Plant Physiology (2023)
Abstract: "Brassinosteroids (BRs) participate in the regulation of plant growth and development through BRI1-EMS-SUPPRESSOR1 (BES1)/BRASSINAZOLE-RESISTANT1 (BZR1) family transcription factors. Cotton (Gossypium hirsutum) fibers are highly elongated single cells, and BRs play a vital role in the regulation of fiber elongation. However, the mode of action on how BR is involved in the regulation of cotton fiber elongation remains unexplored. Here, we generated GhBES1.4 over expression lines and found that overexpression of GhBES1.4 promoted fiber elongation, whereas silencing of GhBES1.4 reduced fiber length. DNA affinity purification and sequencing (DAP-seq) identified 1531 target genes of GhBES1.4 (GBST), and 5 recognition motifs of GhBES1.4 were identified by enrichment analysis. Combined analysis of DAP-seq and RNA-seq data of GhBES1.4-OE/RNAi provided mechanistic insights into GhBES1.4-mediated regulation of cotton fiber development. Further, with the integrated approach of GWAS, RNA-seq, and DAP-seq, we identified seven genes related to fiber elongation that were directly regulated by GhBES1.4. Of them, we showed Cytochrome P450 84A1 (GhCYP84A1) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase 1 (GhHMG1) promote cotton fiber elongation. Overall, the present study established the role of GhBES1.4-mediated gene regulation and laid the foundation for further understanding the mechanism of BR participation in regulating fiber development."
Authors: Zailong Tian, Yuzhou Zhang, Liping Zhu, Bin Jiang, Huiqin Wang, Ruxi Gao, Jiří Friml and Guanghui Xiao.
The Plant Cell (2022)
Abstract: "Strigolactones (SLs) are a class of phytohormones that regulate plant shoot branching and adventitious root development. However, little is known regarding the role of SLs in controlling the behavior of the smallest unit of the organism, the single cell. Here, taking advantage of a classic single-cell model offered by the cotton (Gossypium hirsutum) fiber cell, we show that SLs, whose biosynthesis is fine-tuned by gibberellins (GAs), positively regulate cell elongation and cell wall thickness by promoting the biosynthesis of very-long-chain fatty acids (VLCFAs) and cellulose, respectively. Furthermore, we identified two layers of transcription factors (TFs) involved in the hierarchical regulation of this GA-SL crosstalk. The top-layer TF GROWTH-REGULATING FACTOR 4 (GhGRF4) directly activates expression of the SL biosynthetic gene DWARF27 (D27) to increase SL accumulation in fiber cells and GAs induce GhGRF4 expression. SLs induce the expression of four second-layer TF genes (GhNAC100-2, GhBLH51, GhGT2, and GhB9SHZ1), which transmit SL signals downstream to two ketoacyl-CoA synthase genes (KCS) and three cellulose synthase (CesA) genes by directly activating their transcription. Finally, the KCS and CesA enzymes catalyze the biosynthesis of very long chain fatty acids and cellulose, respectively, to regulate development of high-grade cotton fibers. In addition to providing a theoretical basis for cotton fiber improvement, our results shed light on SL signaling in plant development at the single-cell level."
Authors: Yang Zhang, Yingying Liu, Xueying Wang, Ruiqi Wang, Xuebing Chen, Shuang Wang, Hairong Wei and Zhigang Wei.
Frontiers in Plant Science (2022)
Abstract: "WUSCHEL-related homeobox (WOX) genes are plant-specific transcription factors (TFs) involved in multiple processes of plant development. However, there have hitherto no studies on the WOX TFs involved in secondary cell wall (SCW) formation been reported. In this study, we identified a Populus trichocarpa WOX gene, PtrWOX13A, which was predominantly expressed in SCW, and then characterized its functions through generating PtrWOX13A overexpression poplar transgenic lines; these lines exhibited not only significantly enhanced growth potential, but also remarkably increased SCW thicknesses, fiber lengths, and lignin and hemicellulose contents. However, no obvious change in cellulose content was observed. We revealed that PtrWOX13A directly activated its target genes through binding to two cis-elements, ATTGATTG and TTAATSS, in their promoter regions. The fact that PtrWOX13A responded to the exogenous GAs implies that it is responsive to GA homeostasis caused by GA inactivation and activation genes (e.g., PtrGA20ox4, PtrGA2ox1, and PtrGA3ox1), which were regulated by PtrWOX13A directly or indirectly. Since the master switch gene of SCW formation, PtrWND6A, and lignin biosynthesis regulator, MYB28, significantly increased in PtrWOX13A transgenic lines, we proposed that PtrWOX13A, as a higher hierarchy TF, participated in SCW formation through controlling the genes that are components of the known hierarchical transcription regulation network of poplar SCW formation, and simultaneously triggering a gibberellin-mediated signaling cascade. The discovery of PtrWOX13A predominantly expressed in SCW and its regulatory functions in the poplar wood formation has important implications for improving the wood quality of trees via genetic engineering."
Authors: HE, Peng, HANG, Hui-zhi, ZHANG, Li, JIANG, Bin, XIAO, Guang-hui and YU, Jia-ning.
Journal of Integrative Agriculture (2022)
Abstract: "Strigolactones (SLs) are a new type of plant endogenous hormones that have been found to regulate plant growth and architecture. At present, some genes related to the biosynthesis and signaling pathway of SLs have been isolated in plants such as Arabidopsis thaliana, Pisum sativum and Oryza sativa. However, the signaling pathway and specific mechanism of SLs in cotton remain unclear. In this study, we identified the SLs signaling gene GhMAX2 and demonstrated its function in plant growth and architecture in Gossypium hirsutum. Bioinformatics analysis showed that GhMAX2 mainly consists of an α-helix and a random coil and includes a large number of leucine-rich repeats. GhMAX2 was highly expressed in root, stem, flower, and fibers at 20 days post-anthesis (DPA). GhMAX2 promoter-driven β-glucuronidase expression was present exclusively in the root, main inflorescence, flower, and silique. Subcellular localization showed that GhMAX2 is targeted to the nucleus. Heterologously expressed GhMAX2 can rescue the phenotype of Arabidopsis max2-1 mutant, indicating that the function of MAX2 is highly conserved between G. hirsutum and A. thaliana species. In addition, the knockdown expression of GhMAX2 in cotton resulted in significantly reduced plant height, slow growth, short internodes, and reduced fiber length. These findings indicate that GhMAX2 probably contributes to plant growth, architecture and fiber elongation in cotton. The study reveals insights into the roles of GhMAX2-mediated SL/KAR signaling in cotton and provides a valuable foundation for the cultivation of cotton plants in the future."
Authors: Liping Zhu, Bin Jiang, Jiaojie Zhu and Guanghui Xiao.
Plant Biotechnology Journal (2022)
Excerpts: "Targeted expression IAA biosynthesis gene enhances both fiber yield and quality (Zhang et al., 2011). Exogenous application of GA also improved fiber length (Shan et al., 2014). However, mechanism by which auxin and GA promote cotton fiber development and whether there is cross-talk between them remains unclear. Our study shows that auxin promotes fiber development by enhancing GA biosynthesis."
"The results showed that IAA and GA1 promoted fiber elongation, N-1-naphthylphthalamic acid (NPA, a polar auxin transport inhibitor) and paclobutrazol (PAC, a GA biosynthesis inhibitor) inhibited fiber development. GA1 rescues fiber elongation inhibited by NPA, whereas IAA didn’t rescue shortened fibers by PAC treatment (Figure. 1a), suggesting that GA may function downstream of IAA in regulating fiber development."
"Our results demonstrate that auxin regulates GA biosynthesis through GhARF18 regulating the transcription of GhGA3OX4D and GhGA20OX1D-2 to promote fiber elongation (Figure. 1af)."
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