Anthocyanin regulatory mutations in pea: effects on gene expression and complementation by R-like genes of maize

Abstract

Anthocyanin production in higher plants is a function of the tissue considered and its developmental stage, and is modulated by environmental factors. In maize, the best characterized system, regulation of the pathway is achieved largely through the action of proteins with homology to the transcriptional factors encoded by myc and myb proto-oncogenes of animals; these homologues control the expression of structural genes and thus regulate the availability of anthocyanin biosynthetic enzymes. 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 genes encoding chalcone synthase, flavanone 3β-hydroxylase, and dihydroflavonol 4-reductase in developing flowers. Patterns of expression for these biosynthetic genes in both a and a ₂ mutants confirm the regulatory roles of the two a loci. The reduced expression of all three biosynthetic 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 ability of two maize R-like genes, Lc and R-S, but neither myb-like genes nor R-like genes from snapdragon or petunia, functionally to complement a and a ₂ mutations. We cannot distinguish whether a and a ₂ act coordinately 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 regulatory cascade.