Mechanisms of BES1-regulated gene expression downstream of brassinosteroid signaling in Arabidopsis thaliana

Abstract

Plant steroid hormones, brassinosteroids (BRs), are of great importance for plant growth and development. BRs signal through a cell surface receptor kinase, BRI1, and a GSK3-like kinase, BIN2, to regulate BES1/BZR1 family of transcription factors, which directly bind to target gene promoters to activate or repress gene expression and mediate BR responses. To understand how BES1 regulates target gene expression, we identified two BES1-interacting proteins, ELF6 (Early Flowering 6) and its homolog REF6 (Relative of Early Flowering 6), both of which are Jumonji N/C (JmjN/C) domain-containing proteins and were previously found to regulate flowering time. The interactions between BES1 and ELF6/REF6 were confirmed by GST pull-down and BiFC (Bimolecular Fluorescence Complementation) experiments. Mutations in ELF6 or REF6 genes in Arabidopsis lead to BR-related phenotypes, including impaired cell elongation and reduced expression of BR target genes. Chromatin immunoprecipitation (ChIP) experiments indicated that Histone 3 Lysine 9 (H3K9) methylation status was changed in elf6 and ref6 mutants, consistent with recent findings that many Jmj proteins are histone demethylases. Our results demonstrate that BES1 recruits other transcriptional regulators such as ELF6 and REF6 to regulate target gene