The miR319-Targeted GhTCP4 Promotes the Transition from Cell Elongation to Wall Thickening in Cotton Fiber.

Abstract Plant cell growth involves a complex interplay among cell wall expansion, biosynthesis, and in specific tissues secondary cell wall (SCW) deposition, yet their coordination remains elusive. The cotton fiber cells are developmentally synchronous, highly elongated and contain nearly pure cellulose when mature. Here, we report that the transcription factor GhTCP4 plays an important role in balancing the cotton fiber cell elongation and wall synthesis. During fiber development the miR319 expression declines and the GhTCP4 level increases, with high level of the later promoting SCW deposition. GhTCP4 interacts with a homeobox-containing factor GhHOX3 antagonistically to repress cell elongation, generating a temporal control of fiber cell transition to the SCW stage. We show that overexpression of GhTCP4A advanced and up-regulated the SCW biosynthetic pathway in fiber cell, as revealed by transcriptome and promoter activity analyses, and resulted in shorter fiber with varied lengths and thicker wall. In contrast, GhTCP4 downregulation led to slightly longer fiber of thinner cell wall. The GhHOX3-GhTCP4 complex may represent a general mechanism of cellular development in plants since both factors are conserved, and provides molecular tools for fiber traits design.