Della Proteins Regulate Ga Synthesis and Root Growth Signal Transduction and Hormone Action the Pea (pisum Sativum) 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 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 characterised in other species (Arabidopsis and grasses) as " repressors " of growth, which are destabilised by GAs. Mutations la and cry-s encode non-functional 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 GA synthesis gene expression, as well as inhibit elongation. We show also that one of the DELLA-regulated genes is a new member of the pea GA 3-oxidase family, and that this gene appears to play a major role in pea roots.