Suppression Of Chitinase-Like Genes (CTLs)Expression Promotes Cotton Fiber Late Elongation

Many genes are needed to be involved in cotton fiber secondary cell wall synthesis. Chitinase-like gene (CTL), its expression was predominantly increasing in the secondary wall thickening stage, may be one of them. Two chitinase-like genes, GbCTL1and GbCTL2, were cloned in early studies in our laboratory by expression profile analysis of genes related to island-cotton fiber development. By blasting against cotton EST library TIGR, only two CTL members were found. Real-time PCR analysis showed that the expression of CTL1was slightly higher than CTL2, and reached expression peak slightly earlier than CTL2. The expression of CTL1and CTL2starting at15DPA. Then their expression levels increased rapidly and continued until the end of the second cell wall synthesis period. The expression levels in other tissues is very low or even undetectabled. In order to verify CTLs’ function in cotton fiber secondary cell wall synthesis,35S overexpression and RNAi vectors were constructed and transformed into Gossypium hirsutum cv. YZ1. The transgenic lines with low-copy inserts and significant expression change were selected by Southern blotting hybridization and expression analysis. Then the fiber traits of these lines were investigated. RNA interference suppression of CTL increased fibers length and constitutive overexpression resulted fibers shorter. Other traits such as strength, micronaire, did not change significantly. CTLs’ expression change didn’t affect fiber cellulose content or the thickness of secondary. To investigate whether other genes expressions were regulated in the transgenic lines, the published secondary cell wall synthesis related gene expression were checked. The results showed that in RNAi transgenic lines expression of Expansin that positively correlated with fiber elongation increased. The expression of GhGlucl, callose-degrading enzyme, was decreased. The gene expression pattern of these two genes in overexpression lines was opposite. It should suggest that in RNAi lines Expansin expression up-regulation and GhGluc1expression down-regulation can increase the flexibility of the fiber cell wall to stretch. More research were needed for elucidate GbCTLs function mechanism in fiber development, but the findings in this study implied that in breeding decreasing CTLs expression can improvement cotton fiber quality by increasing length.