Myb26: a MYB-like protein of pea flowers with affinity for promoters of phenylpropanoid genes.

Plant Myb proteins represent a group of transcription factors which have a DNA-binding domain similar to that found in the products of the animal myb proto-oncogenes. Members of the Myb family regulate the biosynthesis of phenylpropanoids, including anthocyanin and phlobaphene pigments, in several species. In this study, PCR with degenerate primers was used to analyse the presence of myb-like genes in pea (Pisum sativum L.). A fragment representing a flower bud-expressed gene, designated myb26, was recovered, and a full length cDNA was isolated from a pea flower bud cDNA library. The predicted protein is 217 amino acids long and its Myb-domain and carboxy terminal region show extensive homology to the snap-dragon proteins Myb305 and Myb340, both of which regulate phenylpropanoid biosynthesis. Expression of myb26 is flower-specific and parallels the expression of flavonoid biosynthetic genes, increasing as the flower bud matures and intensifies in colour. However, myb26 represents neither of the two known regulatory genes for anthocyanin production in pea, nor does it complement mutants of the myb-like anthocyanin regulatory gene an2 in petunia. Myb26 was expressed in E. coli as a fusion protein. It was shown that in vitro Myb26 recognizes the c-Myb and P-box-like binding sites representing cis-elements in the promoter regions of several phenylpropanoid biosynthetic genes. The results suggest that myb26 is a previously undefined gene involved in regulation of some aspect of phenylpropanoid production in pea.