Mutation of a U-box E3 ubiquitin ligase results in brassinosteroid insensitivity in rice

Abstract

Brassinosteroid (BR) is a natural product that promotes plant growth and development. In this paper, we report that the mutation of a U-box E3 ubiquitin ligase reduces BR sensitivity in rice (Oryza sativa L.). A spontaneous dwarf mutant, designated d1352, was identified from the maintainer line 1352. The plant height and grain length of d1352 decreased by 66 and 36 %, respectively, compared with those of wild-type (WT) rice. Anatomical investigation revealed that all mutant internodes were sharply shortened when compared with their WT counterparts, and the relative ratio of each internode suggested a d6-type mutation of d1352. Analysis using exogenous gibberellin (GA) and BR treatment showed that d1352 had normal sensitivity to GA but had reduced sensitivity to BR treatment compared with the WT. The mutant gene d1352 was located in a 98-kb region on rice chromosome 3 by employing a map-based cloning strategy. Sequencing comparison revealed a 24-bp insertion in the coding region of a putative U-box E3 ubiquitin ligase (LOC_Os03g13010), which led to the insertion of eight amino acids in the conserved domain of U-box. Linkage analysis in all populations showed that the insertion was co-segregated with the dwarf phenotype, indicating that the insertion of LOC_Os03g13010 was responsible for the mutant phenotype. The transcription levels of several BR-related genes were also significantly altered in d1352. In conclusion, D1352 has an important function in the BR signaling pathway.