MYB21 interacts with MYC2 to control the expression of terpene synthase genes in flowers of F. hybrida and A. thaliana.

Previously, linalool was found to be the most abundant component among the volatile cocktails released from flowers of Freesia hybrida, which was catalyzed by a monoterpene synthase FhTPS1. However, the regulatory network developmentally modulating the expression of FhTPS1 gene remains unexplored. In this study, three regulators, FhMYB21L1, FhMYB21L2 and FhMYC2, were screened from 52 candidate regulatory genes. The two MYB regulators were synchronously expressed with FhTPS1 and could activate its expression significantly when overexpressed, and the binding of FhMYB21L2 to the MYBCORE sites in FhTPS1 promoter was further confirmed, indicating its direct activation roles. FhMYC2 showed an adverse expression pattern compared with FhTPS1, it could decrease the binding of FhMYB21 against FhTPS1 promoter to counteract its activation capacity when co-expressed, indicating roles of the MYB-bHLH complex in the regulation of FhTPS1 gene. In Arabidopsis thaliana, both MYB21 and MYC2 regulators were proved to activate the expression of sesquiterpene synthase genes, and the regulation roles of AtMYB21 and AtMYC2 on linalool synthase gene was also confirmed, implying conserved functions of the MYB-bHLH complex in these two evolutionarily divergent plants. Moreover, the expression ratio between MYB21 and MYC2 orthologous might be determinant factor for the flower linalool emission.