Ricebending lamina 2 (bla2) mutants are defective in a cytochrome P450 (CYP734A6) gene predicted to mediate brassinosteroid catabofism

Abstract

Desirable morphological traits in rice plants, such as shorter stalks and erect leaves, are being pursued in breeding programs. Rice brassinosteroid (BR)-deficient mutants display the phenotype of reduced heights and erect lamina. Therefore, biotechnology can be used for controlled deactivation of bioactive BRs in specific tissues. Here, we isolated a gene encoding for a BR-deactivating enzyme. Based on its sequence identity with a known enzyme,Arahidopsis Cytochrome P450 734A1, we identified a rice homolog named QsCYP734A6 (LOC_Os01 g29150). A search of the rice T-DNA mutant population for insertional mutants of this gene revealed two alleles. These T-DNA loss-of-function mutants displayed a strongly bending lamina phenotype similar to the morphology of rice plants treated with BRs. These two mutants were namedbending lamina (bla)2-1 andbla2-2. InArahidopsis, the transcript level of a putative BR biosynthetic gene,OsDWARF4, is feed-back down-regulated in response to exogenous application of BRs. Similarly, a steady-state level ofOsDWARF4 transcripts was significantly down-regulated here in the bla2 mutant background. Based on their sequence similarity, the bending-Iamina phenotype in thebla2 mutant, and down-regulation of the BR biosynthetic geneQsDWARF4, we therefore propose that OsCYP734A6 (BLA2) is likely to be involved in BR deactivation.