Fiber-specific Regulations Of GhPIS And GhPSS In Cotton, And Their Effects On Fiber Development

Cotton is the most important natural fiber crops in the world. With extremely elongated structure and composed of nearly pure cellulose, cotton fiber is also an ideal model for studying plant cell elongation and secondary wall accumulation. Lipid metabolisms play vital roles in plant development, however little is known of their functions in fiber development.Phosphatidylinositol and phosphatidylserine are two important components of the cellular phospholipids, with low content in the cell, but crucial roles in the growth and development of plants. Phosphatidylinositol synthase(PIS) is a key enzyme for phosphatidylinositol(PI)biosynthesis. Phosphoinositides(PIs), the phosphorylated derivatives of phosphatidylinositol, are involved in cell polar growth, signal transduction, various biotic and abiotic stress responses.Phosphatidylserine synthase(PSS) is an important enzyme for the biosynthesis of phosphatidylserine. Previous studies showed that AtPSS participated in pollen and inflorescence development in Arabidopsis. To reveal the effect of phosphatidylinositol and phosphatidylserine on cotton fiber development, in this paper, fiber-specific promoter was used for up- and downregulations of the expression of GhPIS or GhPSS in cotton, and the alteration of transgenic cotton fibers was observed. The main results are as follows:1. Expression pattern of GhPIS and GhPSS during fiber developmentRelative expression levels of GhPIS and GhPSS in various development stages of the cotton fiber were detected by quantitative real-time PCR. GhPIS showed a high expression level during fiber elongation and secondary cell wall biosynthesis stages. GhPSS had a high expression level in secondary cell wall synthesis stage. These results implied that GhPIS might be involved both in fiber elongation and secondary cell wall biosynthesis and GhPSS mainly in the secondary wall accumulation.2. Phosphatidylinositol 3-kinase inhibitor, LY294002, suppressed fiber elongationPhosphatidylinositol 3-kinase(PI3K) is inhibited by LY294002. Fiber elongation was blocked after 13-d culture with the inhibitor. It was speculated that phosphoinositides derived from phosphatidylinositol signaling pathway has a role in fiber elongation.3. Up- and down-regulations of GhPIS in the cotton fiber and their effects on fiber developmentA fiber-specific promoter, SCFP, was used to control the expression of GhPIS in fiber. The results of thin layer chromatography(TLC) showed that PI content was increased slightly in the up-regulated cotton fiber(22 DPA) compared to wildtype. However, no much change of GhPIS expression was observed in ovules of the transgenic cotton. The fiber length of the GhPIS up-regulated fibers was increased by 8.7% compared with wildtype. On the contrary,down-regulation of GhPIS decreased PI content in the fiber. These results indicated that the GhPIS had biological function in phosphatidylinositol synthesis, and the fiber specific increase of GhPIS might promote fiber elongation.4. Up- and down-regulations of GhPSS in the cotton fiber and their effects on fiber developmentThe relative content of fatty acids in 22 DPA fibers was determined by GC-MS. Compared to the wildtype, the content of unsaturated fatty acids(18:2 and 18:3) were increased in GhPSS up-regulated fiber cells, whereas decreased in down-regulated cells. Interestingly, expression levels of cellulose synthases(GhCESAs) corresponding for secondary cell wall synthesis in down-regulating lines were dramatically decreased. Consistently, the lint percentage and micronaire value, a quality indicator for cotton fiber fineness were reduced in the GhPSS down-regulated fibers.In conclusion, down-regulation of GhPSS can decrease relative content of unsaturated fatty acids in fiber cells, and interfere the cellulose deposition, leading to a decrease of lint percentage and micronaire value. This study suggests that GhPSS has an important role in regulating secondary cell wall synthesis.