Effects of secondary mutation in det2-1 on root growth and development in Arabidopsis

Abstract

Brassinosteroids (BRs) are plant steroidal hormones that regulate a wide range of developmental processes. Most BR mutants display impaired growth and responses to developmental and environmental stimuli. Here, we found a BR-deficient mutant det2-1 that displayed exceedingly short roots and agravitropic growth, which were not present in other BR mutants. By back-crossing det2-1 with the wild type, we isolated a secondary mutation named det2-1 phenotype modifier 1 (dpm1) and demonstrated that those aberrant phenotypes in the original det2-1 were independent of the BR deficiency. Phenotypic analysis showed that impaired root growth of dpm1 appeared in BR-deficient condition, but not in a normal condition. In the light condition, the mutant showed enhanced shoot growth which was suppressed in the det2-1 background. Starch granules in the columella cells of the root tip were highly accumulated and expanded in dpm1. Agravitropic roots and the expanded starch granules of dpm1 could not be recovered by BR. Taken together, these results suggest that DPM1 is required for gravitropic growth, and that its functions on root and shoot growth are BR-dependent.