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

Four cotton fiber cDNAs (GhMyb7, 8, 9, and 10) and their corresponding genes, encoding R2R3-MYB proteins, have been isolated and characterized from the allotetraploid cotton (Gossypium hirsutum L. cv. DES 119). Genomic origin analysis reveals that GhMyb7 and 9, as well as GhMyb8 and 10, are alloallelic genes in the allotetraploid cotton. Both GhMyb7 and 10 are derived from the A₂ subgenome, whereas GhMyb8 and 9 are from the D₅ subgenome. Northern blot analysis shows that GhMyb10 is expressed in all examined tissues; however, GhMyb7 is expressed in flowers and fibers only, and its expression in fibers is developmentally regulated. The E. coli expressed GhMYB7 fusion protein is able to bind to the promoter region (nt −614 to −544) of Ltp3, a cotton-fiber specific gene, in an in vitro DNA-protein binding assay. The DNA-binding motifs of GhMYB7 and 10, “CC/GTT/AT/A” and “C/GT/ACT/AA/T”, respectively, have been identified by using a random oligonucleotide selection method. The 5′-flanking region of the GhMyb7 gene contains auxin responsive element (AuxRE) and the binding site (TGTCTC) of auxin responsive factor (ARF). Auxin treatment increases the GhMyb7 transcript level in fiber cells in an in vitro ovule culture system. A 0.9-kb promoter region of the GhMyb7 gene can direct the expression of the GUS reporter gene in young leaves and meristems of transgenic tobacco plants. Overexpression of the GhMyb7 gene in tobacco and Arabidopsis plants causes a pleiotropic effect in plant development. Transgenic tobacco plants that overexpress the GhMyb10 gene, however, show a normal development process, but with abnormal cell shapes in leaf trichomes. Analysis of root proteins by 2-D PAGE (two-dimensional polyacrylamide gel electrophoresis) indicates that there are differences in protein profiles between the wild type and 35S-GhMYB7 transgenic tobacco plants.