We have two major lines for our research: understanding the reaction mechanism of biosynthesis of very-long-chain fatty acids (VLCFA); VLCFAs and other lipids modulating cotton fiber cell elongation; cotton lipidomics
Very-long-chain fatty acids (VLCFAs, >C20) are wildly distributed in nature, and they are found mainly in membrane sphingolipids, epi-cuticular waxes, seed storage triacylglcerols of most plant species. VLCFAs are synthesized by the microsomal fatty acid elongation system, which consists of four sequential reactions. Through microarray transcriptome profiling of cotton fiber UniESTs, we identified cDNAs encoding enzymes involved in VLCFA biosynthesis that were preferentially expressed during the fast fiber elongating period. The cotton cDNAs encoding 3-ketoacyl-CoA synthase (KCS), 3-ketoacyl-CoA reductase and trans-2-enoyl-CoA reducatse, were cloned, and functionally characterized by heterologous expressing in yeast mutants. With regarding to the function of VLCFAs in cotton cells, we reported that many VLCFA biosynthetic genes are up-regulated during early cotton fiber development. Further, we recently found that saturated VLCFAs promote cotton fiber and Arabidopsis cell elongation by activating ethylene biosynthesis gene ACOs, providing an important link between the VLCFA biosynthesis and cotton fiber elongation.
By using high-throughput lipid profiling technology based on electrospray ionization tandem mass spectrometry (ESI-MS/MS), we found that fiber cells contained significantly higher amounts of phosphatidylinositol (PI) than both ovule samples with PI 34:3 being the most predominant species. The genes encoding fatty acid desaturases (15GhFAD), PI synthase (PIS) and PI kinase (PIK) were expressed in a fiber-preferential manner. Exogenously applied linolenic acid (C18:3), Soybean L-α-PI and PIPs containing PIP 34:3 promoted significant fiber growth. The growth inhibitory effects of Carbenoxolone, 5-Hydroxytryptamine and Wortmannin were reverted by C18:3, PI or PIP, respectively, suggesting that PIP signaling is essential for fiber cell growth. Furthermore, cotton plants expressing virus-induced gene-silencing constructs that specifically suppressed Gh15FAD, GhPIS or GhPIK expression, resulted in significantly short-fibered phenotypes.