GhHDZ50 regulates cotton fiber elongation in Gossypium hirsutum L. through control of fatty acid biosynthesis.

Cotton fibers are highly elongated single-celled trichomes that develop on the ovule of the seed. However, there are still many unknowns about the molecular mechanism of cotton fiber development. In this study, a homologous domain leucine-zipper (HD-Zip) IV gene GhHDZ50 was reported to play an important role in cotton fiber elongation. GhHDZ50 was predominantly expressed in fibers at 5 days post-anthesis (DPA), and its gene product was localized to the nucleus. Overexpression of GhHDZ50 in Arabidopsis resulted in longer leaf trichomes and root hairs, while knocking out of GhHDZ50 in cotton, resulted in shorter cotton fibers. Knockout of GhHDZ50 in cotton led to reduce transcript levels of genes associated with fatty acid biosynthesis, ethylene biosynthesis and signal transduction, sucrose synthase and tubulin. Biochemical analysis showed that GhHDZ50 interacted directly with GhTCP3, which further inhibited the transcriptional activity of GhHDZ50 on downstream fatty acid synthesis-related genes GhLAC6 and GhLOX5. In conclusion, GhHDZ50 positively regulates cotton fiber elongation through fatty acid biosynthesis. The results provide new evidence for involvement of HD-Zip transcription factors in regulation of cotton fiber development and suggest new targets for cotton breeding.