Influence Of Brassinosteroid On Jasmonate-induced Anthocyanin Accumulation In Arabidopsis Seedlings

Jasmonate (JA), a new class of endogenous hormones, regulates plant development, mediates defense responses, and induces anthocyanin biosynthesis as well. Recently, we isolated the pscl mutant that partially suppressed coil insensitivity to JA, and found that brassinosteroid (BR) was involved in JA signaling and negatively regulated JA inhibition of root growth in Arabidopsis. In order to investigate the interaction between BR and JA signaling, it was analyzed whether BR affected JA-induced anthocyanin accumulation. The results were as follows:1. BR positive regulated JA-induced anthocyanin accumulationIn this study it was shown that the JA-induced anthocyanin accumulation was reduced in BR mutants or in wild type treated with brassinazole, an inhibitor of BR biosynthesis, whereas was induced by an application of exogenous BR. We also found that exogenous BR enhanced JA-induced anthocyanin accumulation in BR biosynthesis defect mutant, but did not work in signaling defect mutant. These results suggested that BR positive regulated the JA-induced anthocyanin accumulation by BR signaling.2. The molecular mechanism of BR effect on JA-induced anthocyanin accumulationThe result of analysis on the molecular level shew that the expression level of CHS and CHI, which are 'early' genes in anthocyanidins synthetic way, didn't vary significantly in Arabidopsis seedings treated with jasmonate. However, the 'late' anthocyanin biosynthesis genes including DFR, LDOX, and UF3GT, decreased in the BR mutants dwf4 and bril compared to wild type. Furthermore, the expression of JA-induced Myb transcription factor PAP1, an important component of WD-repeat/Myb/bHLH transcriptional complexes that mediate the 'late' anthocyanin biosynthesis genes, was lower in BR mutants than that in wild type. These results suggested that BR affects the JA-induced anthocyanin accumulation by regulating the 'late'anthocyanin biosynthesis genes and this regulation might be mediated by the WD-repeat/Myb/bHLH transcriptional complexes.