The Functional Characterizations Of Fiber Elongation Related Gene GbTCP

Cotton, one of the most important economic crops worldwide, occupies an important position in our national economy. Cotton fiber, the important natural plant fiber mainly used for textile industry, develops from individual epidermal cells on the outer integument of the ovules. The quality, as well as the yield, of cotton fiber has a direct impact on the textile industry development and national economic income of our country. Therefore, fiber quality improvement has been a main target of cotton breeding.In our previous research, GbTCP, a member of class I TCP family, which was isolated from the normalized cDNA library of sea-island cotton fiber, was preferentially expressed in the elongating cotton fibers. We found that RNA interfere(RNAi) of GbTCP resulted in shorter fibers in cotton, indicating that GbTCP might positively regulate the fiber elongation. In this study, we developed overexpression transgenic cotton lines driven by ovule-coat-specific promoter PFBP7 and elongating-fiber-specific promoter GbEXPA2 promoters(PPFBP7 and PGbEXPA2) via agrobacterium-mediated transformation. Investigation of fiber quality showed that PFBP7 overexpression lines had longer and thinner fibers, while PGbEXPA2 overexpression lines had shorter and thicker fibers. However, lint percent of each overexpression line did not show significant change compared to WT. Observation about the transverse sections of mature fibers via scanning electron microscope showed that the cell wall of overexpression lines driven by PPFBP7 was thinner, while PGbEXPA2 overexpression lines had thicker cell wall. Further analysis revealed that the contents of JA in 0 DPA ovules of all overexpression lines were higher than those of WT lines. In 10 DPA fibers, JA equally accumulated in PFBP7 overexpression lines and WT, while superiorly accumulated in PGbEXPA2 overexpression lines than WT. Meanwhile, the expression levels of genes involved in JA synthesis and signaling transduction in overexpression lines were upregulated, which was consistent with JA content accumulation in 0 DPA ovules of overexpression lines in. JA signal has been reported to have certain influence on fiber elongation, so we supposed that GbTCP might promote fiber development by regulating JA biosynthesis and response. In addition, we found that genes related to secondary cell-wall thickening were also significantly up-regulated in 10 DPA fiber of PGbEXPA2 lines. Therefore, thicker and shorter fiber in PGbEXPA2 lines might also be resulted from the earlier stepping in the secondary wall thickening period, which inhibited the elongation of fiber.