BdBRD1, a brassinosteroid C-6 oxidase homolog in Brachypodium distachyon L., is required for multiple organ development

Brassinosteroids (BRs), known as a kind of phytohormones, play essential roles in plant growth and development. Although the studies on the BR biosynthesis and signaling are extensive in Arabidopsis, little is known in temperate cereals. In this study, bdbrd1-1, a T-DNA insertion mutant from Brachypodium distachyon, was isolated and characterized in details. The bdbrd1-1 mutant showed lots of cellular and morphogenetic defects, including shortened cell shapes, severe dwarfing, twisted leaves and sterile spikes. Sequencing the flanking fragment of the T-DNA and complementation by genomic DNA in the mutant, confirmed that the developmental defects are caused by the T-DNA insertion in BdBRD1, a possible brassinosteroid C-6 oxidase gene. Application of 24-epicastasterone could partly rescue the bdbrd1-1 dwarfing phenotype. Expression analysis of BdBRD1 suggested that bdbrd1-1 is probably a null mutant and its wild type transcript is expressed in various tissues and highest in the leaf sheaths. Meanwhile, measurements on leaf numbers of the main stems or days to the emergence of the inflorescences suggested that bdbrd1-1 is late-flowering. The late-flowering phenotype could be converted by vernalization treatment, although there lacks a typical FLC gene in B. distachyon. The current data provide an insight into the relationship between BRs biosynthesis and individual development in B. distachyon, an emerging model plant for the temperate cereals.