CmbHLH110, a novel bHLH transcription factor, accelerates flowering in chrysanthemum

Basic helix–loop–helix (bHLH) transcription factor gene family in plants controls various growth and development aspects; however, the actual roles of these genes in flowering plants are not well known. In this study, a novel bHLH protein CmbHLH110 was found to interact with CmERF110 by in vitro and in vivo experiments, a chrysanthemum ERF110 homolog that acts as a positive flowering regulator. In addition, CmbHLH110 was also found to regulate the flowering of chrysanthemums, overexpression of CmbHLH110 causes chrysanthemums to flower earlier, and suppressed CmbHLH110 leads to delayed flowering. Furthermore, the loss-of-function Arabidopsis mutant of its homologue PERICYCLE FACTOR TYPE-A 5 (PFA5) had a noticeable late flowering phenotype, and CmbHLH110 completely complemented the late flowering phenotype of the pfa5 mutant, whereas heterologous overexpression of CmbHLH110 in Arabidopsis Col-0 caused early flowering. Transcriptome sequencing revealed significant differential expression of flowering-related and circadian clock-related genes in transgenic chrysanthemum. Therefore, we concluded that CmbHLH110, as a novel flowering regulator, could interact with CmERF110 to regulate flowering in chrysanthemum.