Genome-wide identification and characterization of melon bHLH transcription factors in regulation of fruit development

Background: The basic helix-loop-helix (bHLH) transcription factor family is one of the largest transcription factor families in plants, and plays crucial roles in plant development. Melon is one of an important horticulture plants, and is an attractive model plant for studying fruit ripening. However, the bHLH gene family of melon has not been identified yet, and functions in fruit growth and ripening are seldom researched. Results: In this study, 118 bHLH genes were identified in the genome of melon. Phylogenetic analysis illustrated that these CmbHLHs could be classified into 16 subfamilies. Intron distribution pattern analysis of bHLH domain found 13 intron distribution patterns in CmbHLHs. CmbHLH genes were unevenly distributed on chromosomes 1 to 12 of the melon genome, and five CmbHLH s were tandem repeat on chromosomes 4 and 8. Expression characters of CmbHLH genes were studied using the transcriptome data. Tissue analysis of indicated CmbHLH32 high expressed in female flowers and early fruit growth stage. Transgenic plant lines of overexpression of CmbHLH32 were constructed, and overexpression of CmbHLH32 result in early fruit ripening compared to the wild type fruit. Conclusions: The bHLH transcription factor family was identified and analyzed for the first time in the melon, overexpression of CmbHLH32 will affect the ripening time of melon fruit, these findings laid a theoretical foundation for further study on the role of bHLH family members in the growth and development of melon .