The FaesMYB15-FaesELF3 module regulates flowering time, floral organ number, and floral color in red flower long-homostyle common buckwheat

EARLY FLOWERING 3 (ELF3) is a core member of the Evening Complex (EC) and plays a critical role in regulating flowering through the plant circadian clock. R2R3-MYB transcription factors (TFs) control the transcriptional regulation of anthocyanin structural genes involved in anthocyanin accumulation in various plants and also play important roles involved in floral development. However, how ELF3 homologs work together with R2R3-MYB TFs to regulate flowering, floral organ development, and flower color remains unclear. In this study, R2R3-MYB TF FaesMYB15 directly binds to the FaesELF3 promoter and suppresses expression of FaesELF3 in common buckwheat. In addition, overexpression of FaesELF3 in red flower LH Fagopyrum esculentum leads to significantly earlier flowering and rapid plant growth, and results in flowers with increased tepal and stamen numbers and a lighter tepal color in transgenic plant. Moreover, total anthocyanin content in the inflorescence of the 35S::FaesELF3 line was significantly lower than that of the normal red flower LH common buckwheat. FaesELF3 overexpression markedly downregulated the expressions of two core circadian clock genes, FaesPRR5–1 and FaesPRR5-2 , and two AGAMOUS -like MADS-box genes, FaesAGL18 and FaesAGL19 , involved in flowering regulation in transgenic plants. Our study introduces a new regulator module of FaesMYB15-FaesELF3 involved in regulating flowering time, floral color, and floral organ number in crops, providing insights for novel breeding strategies of flowering regulation and flower color modification in common buckwheat.