Abstract
By genetical and biochemical analyses using rice mutants, we have elucidated the nature of GA signaling during the past decade. Now, GA perception has been considered as follows; the binding of GA to GID1 induces the formation of a GID1-GA-DELLA complex and, following the degradation of DELLA with aid of F box protein, GID2, via 26S proteasome pathway, results in various GA-triggered actions. Our recent study on the structure of rice GID1 protein revealed that 1) GID1 resembles hormone sensitive lipase (HSL) and interacts with GA in its binding pocket, 2) bioactive GA is held in its pocket by specific polar and non-polar amino acids via hydrogen bonds and hydrophobic interaction, 3) GID1 evolved by replacement of some important amino acids that were refined for high affinity and specificity to the currently active higher plant GAs.
The next question is why the formation of GID1-GA-DELLA complex induces the interaction between DELLA and GID2. We produced various mutated DELLA and GID2 to determine the regions of DELLA essential for GID2 binding and GID2 for DELLA binding by Y3H. We also examined the effect of these mutations in planta using transgenic plants.
