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[学术文献 ] GhXB38D represses cotton fibre elongation through ubiquitination of ethylene biosynthesis enzymes GhACS4 and GhACO1 进入全文
PLANT BIOTECHNOLOGY JOURNAL
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.
[学术文献 ] Cotton GhNAC4 promotes drought tolerance by regulating secondary cell wall biosynthesis and ribosomal protein homeostasis 进入全文
PLANT JOURNAL
Drought has a severe impact on the quality and yield of cotton. Deciphering the key genes related to drought tolerance is important for understanding the regulation mechanism of drought stress and breeding drought-tolerant cotton cultivars. Several studies have demonstrated that NAC transcription factors are crucial in the regulation of drought stress, however, the related functional mechanisms are still largely unexplored. Here, we identified that NAC transcription factor GhNAC4 positively regulated drought stress tolerance in cotton. The expression of GhNAC4 was significantly induced by abiotic stress and plant hormones. Silencing of GhNAC4 distinctly impaired the resistance to drought stress and overexpressing GhNAC4 in cotton significantly enhanced the stress tolerance. RNA-seq analysis revealed that overexpression of GhNAC4 enriched the expression of genes associated with the biosynthesis of secondary cell walls and ribosomal proteins. We confirmed that GhNAC4 positively activated the expressions of GhNST1, a master regulator reported previously in secondary cell wall formation, and two ribosomal protein-encoding genes GhRPL12 and GhRPL18p, by directly binding to their promoter regions. Overexpression of GhNAC4 promoted the expression of downstream genes associated with the secondary wall biosynthesis, resulting in enhancing secondary wall deposition in the roots, and silencing of GhRPL12 and GhRPL18p significantly impaired the resistance to drought stress. Taken together, our study reveals a novel pathway mediated by GhNAC4 that promotes secondary cell wall biosynthesis to strengthen secondary wall development and regulates the expression of ribosomal protein-encoding genes to maintain translation stability, which ultimately enhances drought tolerance in cotton.
[学术文献 ] LIPID TRANSFER PROTEIN4 regulates cotton ceramide content and activates fiber cell elongation 进入全文
PLANT PHYSIOLOGY
Cell elongation is a fundamental process for plant growth and development. Studies have shown lipid metabolism plays important role in cell elongation; however, the related functional mechanisms remain largely unknown. Here, we report that cotton (Gossypium hirsutum) LIPID TRANSFER PROTEIN4 (GhLTP4) promotes fiber cell elongation via elevating ceramides (Cers) content and activating auxin-responsive pathways. GhLTP4 was preferentially expressed in elongating fibers. Over-expression and down-regulation of GhLTP4 led to longer and shorter fiber cells, respectively. Cers were greatly enriched in GhLTP4-overexpressing lines and decreased dramatically in GhLTP4 down-regulating lines. Moreover, auxin content and transcript levels of indole-3-acetic acid (IAA)-responsive genes were significantly increased in GhLTP4-overexpressing cotton fibers. Exogenous application of Cers promoted fiber elongation, while NPA (N-1-naphthalic acid, a polar auxin transport inhibitor) counteracted the promoting effect, suggesting that IAA functions downstream of Cers in regulating fiber elongation. Furthermore, we identified a basic helix-loop-helix transcription factor, GhbHLH105, that binds to the E-box element in the GhLTP4 promoter region and promotes the expression of GhLTP4. Suppression of GhbHLH105 in cotton reduced the transcripts level of GhLTP4, resulting in smaller cotton bolls and decreased fiber length. These results provide insights into the complex interactions between lipids and auxin-signaling pathways to promote plant cell elongation.
[学术文献 ] Down-regulation of xylan biosynthetic GhGT47Bs in cotton impedes fibre elongation and secondary wall thickening during fibre transition 进入全文
PLANT BIOTECHNOLOGY JOURNAL
Cotton provides abundant natural fibres for the textile industry. Cotton fibre development can be divided into five stages: fibre initiation, elongation, transition, secondary cell wall (SCW) thickening and maturation. Fibre initiation and elongation have been extensively studied, but the transition stage remains less investigated. Although cellulose accounts for >90% of mature fibres, non-cellulosic polysaccharides also contribute to fibre development. Little is known about the roles of these carbohydrates during this process. The hemicellulosic polysaccharide xylan peaked in 17 days postanthesis (dpa) fibres in four cotton species with contrasting fibre characteristics, indicating that xylan may function in the transition stage. GhFSN1 and GhMYB46_D13 positively regulate SCW synthesis in cotton fibres (Huang et al., 2021; Zhang et al., 2018), and overexpression of GhFSN1 or GhMYB46_D13 up-regulated the expression of a set of cell wall-related genes. Two GhGT47B genes (Gh_A13G2031 and Gh_D13G2434, designated as GhGT47B_A13 and GhGT47B_D13, respectively) caught our attention as they are annotated as homologues of AtFRA8, which is involved in xylan biosynthesis in Arabidopsis (Chen et al., 2020; Zhong et al., 2005). A yeast one-hybrid analysis coupled with transactivation assay confirmed that both GhGT47B genes can be activated by GhFSN1 and GhMYB46_D13 (Figure S1a–d). RT-qPCR analysis showed that GhGT47B expression peaked in 15, 18 and 20 dpa cotton fibres, and they represent the most abundantly expressed GhGT47B subclade during fibre transition (Figures S2a and S3). Subcellular localization assays indicated that both GhGT47B proteins were located in the Golgi, where xylan is synthesized (Figure S2b). Next, we silenced both GhGT47B genes in cotton. Fibre phenotype analysis in the T1 and T2 generations revealed that mature fibres of RNAi lines were significantly shorter than those of the wild type (Figure S4). We confirmed these results in two independent RNAi lines of the T3 generation (Figure 1a–c). In addition, the cell wall thickness of mature cotton fibres of RNAi lines was significantly thinner than that of wild type (Figure 1d,e). Fibre quality parameters analyses showed that the length, breaking strength, elongation and micronaire value of fibres in RNAi lines significantly decreased (Table S1). Moreover, the degree of twisting of most cotton fibres of GhGT47B RNAi lines was largely reduced (Figure 1f,g), suggesting that the breaking strength in RNAi fibres declined. We next examined xylan abundance in the RNAi lines by immunolabelling. We found weaker fluorescence intensity of 15 dpa and 21 dpa cotton fibre cell walls of RNAi compared with wild type (Figure 1h). Monosaccharide composition analysis validated that the xylose content significantly decreased in RNAi fibres (Figure 1k). Further NMR analysis showed that the xylan structure in wild-type cotton fibre and Arabidopsis stem appeared largely similar. Interestingly, there is a new peak in the spectrum of cotton (highlighted in the blue rectangular box), which is absent in the Arabidopsis xylan (Figure 1i). Nevertheless, the structure of xylan reducing end sequence (RES) in cotton fibre and Arabidopsis stem is different. G1, R1 and X1 are peaks represented by different monosaccharides constituting the RES. R1 and X1 of cotton fibre can hardly be detected, but the G1 peak is more pronounced, while there is little difference in the height of G1, R1 and X1 peaks in Arabidopsis stem (Figure 1i). Through calculation, the relative abundance of RES in the GhGT47B RNAi lines was 21% lower than that of wild type, implicating GhGT47B activity in the synthesis of xylan RES in cotton fibre. To explore whether the decrease of xylan content impacts cellulose synthesis, we used cellulose-specific fluorescent dye pontamine fast scarlet 4B to stain the fibre resin slices. The fluorescence of 15 dpa, 21 dpa and mature cotton fibres of RNAi transgenic lines was obviously fainter than those of wild type (Figure 1j). These results were corroborated by crystalline cellulose measurements (Figure 1l) and indicate that cotton fibres produce less cellulose when GhGT47B is down-regulated. To further investigate genes and pathways affected by GhGT47B, we sequenced the transcriptome of 18 dpa fibre of GhGT47B RNAi cotton and the wild type. Gene Ontology (GO) enrichment analysis showed that several terms involved in cell wall synthesis and modification were enriched, confirming that GhGT47B is associated with cell wall biogenesis and/or organization (Figure S5a–d). Further analysis showed that genes related to synthesis of xylan backbone, side chain modification and genes involved in cellulose synthesis are among the differentially expressed genes (Figure S5e,f). It is plausible cell wall change is sensed by a monitoring pathway that then regulates growth to ensure sufficient strength during fibre development. Based on the transcriptome analysis, we summarized the mode in which down-regulation of GhGT47B might affect cell wall components (Figure S6). Fibre development requires many cell wall-related genes. Exploring these genes will provide insights into cell wall modifications, with the aim to ultimately make unique cotton fibres to better suit our needs. Our findings support the involvement of xylan in fibre development and might work as a template to manipulate xylan synthesis to fine-tune cell wall composition for fibre improvement.
[学术文献 ] Identification of candidate genes for aphid resistance in upland cotton by QTL mapping and expression analysis 进入全文
CROP JOURNAL
Lignin is one of the main components of cell walls and is essential for resistance to insect pests in plants. Cotton plants are damaged by aphid (Aphis gossypii) worldwide but resistant breeding is undeveloped due to scarce knowledge on resistance genes and the mechanism. This study reported a lignin biosynthesis related gene identified in the F2 population derived from the cross between cotton cultivars Xinluzao 61 (resistant to aphid) and Xinluzao 50 (susceptible to aphid). A quantitative trait locus was mapped on chromosome D04 with a logarithm of odds (LOD) score of 5.99 and phenotypic effect of 27%. RNA-seq analysis of candidate intervals showed that the expression level of GH_D04G1418 was higher in the resistant cultivar than in the susceptible cultivar. This locus is close to AtLAC4 in the phylogenetic tree and contains a conserved laccase domain. Hence, it was designated GhLAC4-3. Silencing of GhLAC4-3 in Xinluzao 61 via virus-induced gene silencing (VIGS) resulted in decreased lignin content and increased susceptibility to aphids. These results suggest that GhLAC4-3 might enhance aphid resistance by regulating lignin biosynthesis in cotton.(c) 2023 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
[学术文献 ] The R2R3-MYB transcription factor GaPC controls petal coloration in cotton 进入全文
CROP JOURNAL
Although a few cases of genetic epistasis in plants have been reported, the combined analysis of genetically phenotypic segregation and the related molecular mechanism remains rarely studied. Here, we have identified a gene (named GaPC) controlling petal coloration in Gossypium arboreum and following a heritable recessive epistatic genetic model. Petal coloration is controlled by a single dominant gene, GaPC. A loss-of-function mutation of GaPC leads to a recessive gene Gapc that masks the phenotype of other color genes and shows recessive epistatic interactions. Map-based cloning showed that GaPC encodes an R2R3-MYB transcription factor. A 4814-bp long terminal repeat retrotransposon insertion at the second exon led to GaPC loss of function and disabled petal coloration. GaPC controlled petal coloration by regulating the anthocyanin and flavone biosynthesis pathways. Expression of core genes in the phenylpropanoid and anthocyanin pathways was higher in colored than in white petals. Petal color was conferred by flavonoids and anthocyanins, with red and yellow petals rich in anthocyanin and flavonol glycosides, respectively. This study provides new insight on molecular mechanism of recessive epistasis, also has potential breeding value by engineering GaPC to develop colored petals or fibers for multifunctional utilization of cotton.(c) 2023 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
