DELLA proteins and GA signalling in Arabidopsis

Gibberellin (GA) is a classical plant hormone involved in many aspects of plant growth and development. A family of five homologs called the DELLA proteins, comprised of GAL RGA, RGL1, RGL2 and RGL3, were recently found to act as critical GA signal mediators in Arabidopsis. Reports have shown that GAI and RGA are coupled together to repress stem elongation growth whereas RGL2 is a major negative regulator of seed germination. GA down-regulates DELLA proteins through protein degradation likely via the proteasome pathway. The conserved and functionally important DELLA domain is responsible for protein stability in response to GA.