Transcriptional regulation of the lipid transfer protein gene LTP3 in cotton fibers by a novel MYB protein

Two cotton fiber cDNAs (GhMyb7 and GhMyb9) and their corresponding genes, encoding R2R3-MYB proteins, have been isolated from the allotetraploid cotton (Gossypium hirsutum L. cv. DES119) and characterized. Genomic origin analysis reveals that GhMyb7 and 9 are alloallelic genes in the allotetraploid cotton (AD genome). GhMyb7 is derived from the A2 subgenome, whereas GhMyb9 is from the D5 subgenome. Northern blot analysis showed that GhMyb7/9 is expressed in flowers and fibers, and its expression in fibers is developmentally regulated. Auxin treatment increases transcript levels of GhMyb7/9 in fiber cells in an in vitro ovule culture system. The Escherichia coli-expressed GhMYB7 fusion protein binds to the promoter region (nt −614 to −580) of Ltp3, a cotton-fiber-specific gene, in an in vitro DNA-protein-binding assay, suggesting that GhMYB7/9 may play a role in the transcriptional regulation of the Ltp3 gene during fiber development. The overexpression of GhMyb7 in both transgenic tobacco and Arabidopsis plants causes a pleiotropic effect on plant development, including dwarf, abnormal leaf shape, and retarded root development. The late-flowering phenotype is observed in the 35S:GhMyb7 transgenic tobacco and Arabidopsis plants under long day (LD) condition. The transgenic Arabidopsis plants, however, show the absence of inflorescence under short day (SD) condition, suggesting that GhMYB7 overexpession might inhibit the GA biosynthesis or signaling pathway.