Abstract:

Besides as a precursor of BL biosynthesis, more and more evidences support the hypothesis that phytosterols possess a BL-independent signaling pathway. Furthermore, the obtusifoliol is regarded as a signal molecule in sterol signaling. To understand the effects of phytosterols on the development of cotton (Gossypium hirsutum L.) fibers and the molecular basic of sterol signaling in cotton fiber growth, we cloned a gene encoding a homologue of obtusifoliol 14α-demethylase from developing fibers of upland cotton cv. Xuzhou 142 through screening cotton fiber EST (Express Sequence Tag) database and contigging the candidate ESTs. The full length of GhCYP51G1 (GenBank accession No. EU727154) was 1 710 bp, including a 160 bp 5'-untranslated region (UTR), a 1461 bp open reading frame (ORF), and an 89 bp 3'-UTR. The GhCYP51G1 encoded a polypeptide of 486 amino acid residues with a predicted molecular mass of 55.2 kD. The deduced amino acid sequences had high homology with the members of CYP51 family in plant kingdom. Moreover, many typical conserved regions were characterized as the obtusifoliol 14α-demethylase, such as substrate recognition sites (SRS) and heme-binding region presented in the deduced protein. Quantitative real-time RT-PCR analysis revealed that the higher expression levels of GhCYP51G1 gene were detected in 8-DPA, 12-DPA, 18-DPA fibers, and 12-DPA ovules. These results indicate that GhCYP15G1 gene plays an important role in fiber elongation. Furthermore, Auxin significantly down regulates the expression level of GhCYP51G1 in cotton fiber growth. This suggested that phytosterols play a role in the interaction of plant hormones, especially brassinosteroids and auxin.

Key words: Cotton fiber, Phytosterols, Obtusifoliol 14α-demethylase, GhCYP51G1, Brassinosteroids