Screening and characterization of an inhibitory chemical specific to Arabidopsis gibberellin 2-oxidases

The hydroxylation of gibberellin (GA) at the 2-position is known as the major cause of inactivation of GAs, whose reaction is catalyzed by 2-oxoglutarate dependent dioxygenases, also termed GA 2-oxidases (GA2oxs). To block GA catabolism in plants, a few chemicals can be used. To obtain novel inhibitors specific to GA2oxs, we performed in vitro random screenings by using 3H-16,17-dihydro-GA4 and recombinant Arabidopsis GA2ox2. As a result, one candidate, methyl 6-chloro-3H-1,2,3-benzodithiazole-4-carboxylate 2-oxide (CBTC), was selected from the screening, and was subjected to in-planta evaluations. CBTC promoted both the germination and elongation of Arabidopsis seedlings. This strongly suggests that CBTC inhibits GA2oxs in Arabidopsis with high specificity.