Abstract: Brassinosteroids (BRs) are an important class of plant steroidal hormones that are essential in a wide variety of physiological processes, including cell division and elongation, vascular differentiation, reproductive development, senescence, biotic and abiotic tolerance. To determine the effects of BRs on development of cotton fibers, we have cloned a key gene (GhDWF1) involved in the upstream biosynthetic pathway of BRs from developing fibers of upland cotton (Gossypium hirsutum L.) cv. XuZhou142. The full length of the cloned cDNA is 1849bp, including a 37bp 5’-untranslated region, an ORF of 1692bp and a 120bp 3’-untranslated region. The cDNA encodes a polypeptide of 563 amino acid residues with a predicted molecular mass of 65 KD. The deduced amino acid sequence has high homology with the BR biosynthetic enzyme, DWARF1/DIMINUTO, from rice, maize, pea, tomato and Arabidopsis. Furthermore, the typical conserved structure, such as the transmembrane domain, the FAD-dependent oxidase domain and FAD-binding site, are present in GhDWF1 protein. Southern blot indicated the GhDWF1 gene has a single copy in upland cotton genome. RT-PCR analysis revealed that the highest level of GhDWF1 expression was detected in 0DPA ovule (with fibers) while the lowest level was observed in cotyledon. The GhDWF1 gene expressed highly in roots, young stems and fibers. Moreover, the expression level was higher in ovules (with fibers) of wildtype (XuZhou142) than in ovules of fuzzless-lintless mutant at the same developmental stages (0DPA and 4DPA). Results suggest that the GhDWF1 gene plays a crucial role in fiber development, especially, in the initiation and the secondary cell wall deposition of fiber cells.

Key words: cotton, DWARF1 gene, fiber, Brassinosteroids, phytosterol