Discovery of Gibberellin Methyltransferases in Arabidopsis

Abstract

Methyltransferases (MT) are involved in a variety of metabolic pathways in plants. We found two Arabidopsis MTs that are able catalyze methylation of gibberellins (GAs) and named them GAMT1 and GAMT2. Ectopic expression of GAMT1 or GAMT2 in Arabidopsis resulted in dwarfism with reduced levels of bioactive GAs. GAMT1 and GAMT2 are both expressed mainly in siliques during Arabidopsis development. Siliques of the plants homozygous for null alleles at the GAMT1 and GAMT2 loci accumulated high levels of various GAs, with siliques of the double mutant showing particularly high levels of GA₁. Seeds of the gamt1 gamt2 double mutant showed reduced inhibition of germination, compared with wild type, in the presence of a GA biosynthesis inhibitor. These results suggest that GAMTs play a role in GA deactivation in Arabidopsis seeds.