MYB26 - A MYB-LIKE PROTEIN OF PEA FLOWERS WITH AFFINITY FOR PROMOTERSOF PHENYLPROPANOID GENES

Plant Myb proteins represent a group of transcription factors which ha ve a DNA-binding domain similar to that found in the products of the a nimal myb proto-oncogenes. Members of the Myb family regulate the bios ynthesis of phenylpropanoids, including anthocyanin and phlobaphene pi gments, in several species. In this study, PCR with degenerate primers was used to analyse the presence of myb-like genes in pea (Pisum sati vum L.). A fragment representing a flower bud-expressed gene, designat ed myb26, was recovered, and a full length cDNA was isolated from a pe a flower bud cDNA library. The predicted protein is 217 amino acids lo ng and its Myb-domain and carboxy terminal region show extensive homol ogy to the snapdragon proteins Myb305 and Myb340, both of which regula te phenylpropanoid biosynthesis. Expression of myb26 is flower-specifi c and parallels the expression of flavonoid biosynthetic genes, increa sing as the flower bud matures and intensifies in colour. However, myb 26 represents neither of the two known regulatory genes for anthocyani n production in pea, nor does it complement mutants of the myb-like an thocyanin regulatory gene an2 in petunia. Myb26 was expressed in E. co il as a fusion protein. It was shown that in vitro Myb26 recognizes th e c-Myb and P-box-like binding sites representing cis-elements in the promoter regions of several phenylpropanoid biosynthetic genes. The re sults suggest that myb26 is a previously undefined gene involved in re gulation of some aspect of phenylpropanoid production in pea.