Biosynthesis Of UDP-Sugars Is Important For Cotton Fiber And Arabidopsis Root Hair Elongation

Cotton fibers are single-celled trichomes differentiated from outer integuments of the ovule. As the most prevalent natural raw materials used in the textile industry, cotton fibers plays a significant role in the global economy. Also, fiber serves as an excellent single-celled model for studying fundamental biological proc esses, such as cell elongation and differentiation Plant primary cell walls consist of mainly pectin, hemicellulose and cellulose, and are deposited during the cell expansion phase. Here, upon 2-DE separation and MALDI-TOF MS analyses, we identified 93 of 101 protein spots that were preferentially accumulated in wild-type cotton ovules,encoded by 66 genes, from wild-type cotton samples. We subjected this dataset to KOBAS and found that cell wall polysaccharide biosynthesis was the most significantly up-regulated bioc hemical pathway in wild-type samples. Proteomic data of 7 protein spots potentially related to nucleotide sugar inter-conversions identified further by Nano-LC-FTICR-MS. The same set of enzymes were accumulated when presence of 0.1μM ethylene, with their transcripts increased after the treatment. Exogenous lignoceric acid (C24:0) showed a similar effect on protein accumulation and gene activation, indicating that these two compounds may indeed promote fiber elongation by sequentially modulating the production of specific cell wall polymers. GC/MS analysis of sugar compositions from non-cellulose wall polysaccharide fractions revealed that fiber primary cell walls contained significantly higher amounts of arabinose, rhamnose and galacturonic acids (GalA) whereas more xylose and glucose were found in ovule samples.When applied in ovule culture media, UDP-rhamnose, precursor of pectic polymer, was able to stimulate significant fiber elongation, while rhamnose was inactive in the same growth assay. The short-root-hair phenotype of Arabidopsis uer1 knock-out mutant was genetically complemented by the cotton UER1 cDNA. Exogenous UDP-rhamnose, not free rhamnose, produced a similar effect when it was included in MS media for Arabidopsis culture. Molecular studies revealed that, in cut1 and ein2-5 Arabidopsis mutants that are known to involve in biosynthesis of C24:0 and ethylene signaling, respectively, the amount of AtUER1 transcripts was significantly reduced. The short root hairs found in the mutants were also rescued only by exogenous UDP-rhamnose, suggesting that C24:0 and ethylene may promote cotton fiber and Arabidopsis root hair growth by upregulating UER1 expression required for production of pectic polymers. Proteomic, metabolomic and genetic studies indicate that biosynthesis of UDP-Rhamnose is important for cotton fiber and Arabidopsis root hair elongationFurther analysis indicate that GAE1 and UXE1 required for biosynthesis of UDP-arabinose and UDP-GalA were preferentially accumulated in cotton fiber cell. When applied in ovule culture media, UDP-arabinose and UDP-GalA, precursors of pectic polymers, were able to stimulate significant fiber elongation, while UDP-xylose, a hemicellulose precursor was inactive in the same growth assay. GAE1 and UXE1 transcripts were increased when 1 dpa wild-type ovules were cultured in the presence of ethylene. Our results indicate that biosynthesis of UDP-sugars that are precursors of pectic polymers is important for cotton fiber elongation.