Identification Of GbTLP1 Function In Cotton Fiber Development

Cotton is an important economic crop around the world. Cotton fibers are single-celled seed trichomes from the outer epidermal cells of the ovules. Cotton fiber development consists of four overlapping stages: initiation(-3~3 days post anthesis [DPA]), elongation/primary cell wall(PCW) synthesis(3~20 DPA), secondary cell wall biosynthesis(SCW)(15~45 DPA) and maturation(45~50 DPA). The initiation stage plays a vital role in cotton fiber yield formation. The elongation stage is a key factor to decide fiber length. The SCW biosynthesis determines fiber quality, such as fiber strength and fineness(micronaire).In our previous study we have constructed a normalized cDNA library of the fiber of Gossypium barbadense 3-79. A thaumatin-like protein gene GbTLP1 that is preferentially and highly expressed in secondary cell wall biosynthesis stage was cloned. By agrobacterium mediated transformation system, the overexpression and RNAi transgenic cotton lines were developed. In this study, cotton fiber quality data of 3 overexpression lines(OE15, OE38, OE48) and 3 RNAi lines(I53, I84, I88) were obtained, which indicated that the fiber length of GbTLP1 overexpression and RNAi lines was both shorter than the wild type YZ1. The micronaire value of overexpression lines was decreased compared to the wild type, and the micronaire of RNAi lines was increased. With scanning electron microscope, we found the thickness of mature fiber of overexpression lines was thinner than the one of wild type and thickness of RNAi lines was thicker than wild type. When we detected the expression of SCW related genes in overexpression line, we found the expression level of GhCESA7 related to SCW biosynthesis was lower in overexpression lines compared to WT. Yeast two hybrid experiments showed that GbTLP1 protein was able to interact with GhRDL1 and GhOsmotin proteins. According to the references GhRDL1 could promote fiber cell elongation and result longer mature fiber and Osmotin could enhance the resistance of the plants to stress. We found that GhOsmotin preferentially expressed in SCW and belonged to PR5. Therefore, we speculate that GbTLP1 interacting with GhRDL1 and GhOsmotin should play a role in the elongation and SCW stages of cotton fiber development.