The Pea DELLA Proteins LA and CRY Are Important Regulators of Gibberellin Synthesis and Root Growth

The theory that bioactive gibberellins (GAs) act as inhibitors of inhibitors of plant growth was based originally on the slender pea (Pisum sativum) mutant (genotype la cry-s), but the molecular nature of this mutant has remained obscure. Here we show that the genes LA and CRY encode DELLA proteins, previously characterized in other species (Arabidopsis [Arabidopsis thaliana] and several grasses) as repressors of growth, which are destabilized by GAs. Mutations la and cry-s encode nonfunctional proteins, accounting for the fact that la cry-s plants are extremely elongated, or slender. We use the la and cry-s mutations to show that in roots, DELLA proteins effectively promote the expression of GA synthesis genes, as well as inhibit elongation. We show also that one of the DELLA-regulated genes is a second member of the pea GA 3-oxidase family, and that this gene appears to play a major role in pea roots.