GhDET2, a steroid 5alpha-reductase, plays an important role in cotton fiber cell initiation and elongation.

Cotton (Gossypium hirsutum L.) fibers, one of the most important natural raw materials for textile industry, are highly elongated trichomes from epidermal cells of cotton ovules. DET2, an Arabidopsis steroid 5d-reductase, is considered to catalyze a major rate-limiting in brassinosteroid (BR) biosynthesis. To understand the role of BRs in cotton fiber development, GhDET2, which putatively encodes a steroid 5alpha-reductase by sequence comparison, was cloned from developing fiber cells. In vitro assessment of GhDET2 protein activity confirmed that GhDET2 encodes a functional steroid 5alpha-redutase. High levels of GhDET2 transcript were detected during the fiber initiation stage and the fiber rapid elongation stage. Antisense-mediated suppression of GhDET2 inhibited both fiber initiation and fiber elongation. Similarly, treating cultured ovules with finasteride, a steroid 5alpha-reductase inhibitor, reduced fiber elongation. Inhibition of fiber cell elongation by expression of antisense GhDET2 or the finasteride treatment could be reversed by epibrassinolide, a biologically active BR. Furthermore, seed coat-specific expression of GhDET2 increased fiber number and length. Therefore, GhDET2 and BRs play a crucial role in the initiation and elongation of cotton fiber cells, suggesting that modulation of BR biosynthesis factors may improve fiber quality or yield.