GA Perception and Signal Transduction: Molecular Interactions of the GA Receptor GID1 with GA and the DELLA Protein SLR1 in Rice

摘要

Gibberellins (GAs) are diterpenoid plant hormones that promote a number of plant growth responses, including seed germination, stem elongation, leaf expansion, and flowering. GAs act by inducing the degradation of DELIA domain proteins that function as repressers of GA-dependent processes. Research over the past few years has uncovered the principal steps associated with GA perception and signal transduction in rice and Arabidopsis. Two years ago, Ueguchi-Tanaka et al. (2005) identified a GA receptorin rice, GIBBERELLIN INSENSITIVE DWARF1 (GID1), which encodes a soluble protein with similarity to hormone-sensitive lipases. Nakajima et al. (2006) cloned three homologous genes in Arabidopsis, called GID1a, GID1b, and GID1c, and confirmed that all three genes encode proteins that bind GA in vitro and rescue the GA-insensitive dwarf phenotype when expressed (individually) in the rice gidl mutant. Recent work by Griffiths et al. (2006), Willige et al. (2007), and luchi et al. (2007) has shown that thegidla gidlb gidlc triple mutant exhibits a severe GA-insensitive dwarf phenotype, demonstrating that these three proteins have overlapping functions as the major GA receptors in Arabidopsis. These studies and others have also shown that the GID1 receptors likely participate in a GA-dependent interaction with the DELLA protein SLR1 in rice and the five DELLA proteins RGA, GAI, RGL1, RGL2, and RGL3 in Arabidopsis. This interaction leads to degradation of the DELLA proteins via the proteasome pathway, thusrelieving DELLA-mediated repression of GA-dependent growth processes (Figure 1). The F-box proteins GID2 in rice (Sasaki et al., 2003) and SLY1 in Arabidopsis (McGinnis et al., 2003) are components of SCF E3 ubiquitin ligases that are predicted to target the DELLA proteins for proteasome-mediated degradation in a GA-dependent fashion.