Abstract
A nuclear Gibberellin (GA) receptor, GIBBERELLIN INSENSITIVE DWARF1 (GID1), has a primary structure similar to that of the hormone-sensitive lipases (HSLs). Here we analyze the crystal structure of rice GID1 (OsGID1) bound with GA4 and GA3 at 1.9 Å resolution. The overall structure of both complexes shows an alpha/beta-hydrolase fold similar to that of HSLs. The GA-binding pocket corresponds to the substrate-binding site of HSLs. On the basis of the OsGID1 structure, we mutagenized important residues for GA binding. The replacement of Ile 133 with Leu or Val, residues corresponding to those of the lycophyte GID1s, caused an increase in the binding affinity for GA34, a 2β-hydroxylated GA4. These observations indicate that GID1 originated from HSL and has been further modified to have higher affinity and more strict selectivity for bioactive GAs by adapting the amino acids involved in GA binding in the course of plant evolution.
