ANTHOCYANIN REGULATORY MUTATIONS IN PEA - EFFECTS ON GENE-EXPRESSION AND COMPLEMENTATION BY R-LIKE GENES OF MAIZE

Anthocyanin production in higher plants is a function of the tissue co nsidered and its developmental stage, and is modulated by environmenta l factors. In maize, the best characterized system, regulation of the pathway is achieved largely through the action of proteins with homolo gy to the transcriptional factors encoded by myc and myb proto-oncogen es of animals; these homologues control the expression of structural g enes and thus regulate the availability of anthocyanin biosynthetic en zymes. We have studied anthocyanin biosynthesis and its regulation in flowers of pea (Pisum sativum). Our results demonstrate a correlation between anthocyanin accumulation and steady-state mRNA levels for gene s encoding chalcone synthase, flavanone 3 beta-hydroxylase, and dihydr oflavonol 4-reductase in developing flowers. Patterns of expression fo r these biosynthetic genes in both a and a(2) mutants confirm the regu latory roles of the two a loci. The reduced expression of all three bi osynthetic genes in mutant lines suggests that genes acting both early and late in the anthocyanin biosynthetic pathway are controlled by a and a(2). Particle bombardment of floral tissue demonstrates the abili ty of two maize R-like genes, Le and R-S, but neither myb-like genes n or R-like genes from snapdragon or petunia, functionally to complement a and a(2) mutations. We cannot distinguish whether a and at act coor dinately or sequentially in anthocyanin regulation, but the epistatic action of maize R-like genes suggests that they mimic the action of a gene that normally functions downstream of both a and a(2) in the regu latory cascade.