| Summary: | The <i>basic helix-loop-helix</i> (<i>bHLH</i>) transcription factor family is one of the largest transcription factor families in plants and plays crucial roles in plant development. Melon is an important horticultural plant as well as an attractive model plant for studying fruit ripening. However, the <i>bHLH</i> gene family of melon has not yet been identified, and its functions in fruit growth and ripening are seldom researched. In this study, 118 <i>bHLH</i> genes were identified in the melon genome. These <i>CmbHLH</i> genes were unevenly distributed on chromosomes 1 to 12, and five <i>CmbHLHs</i> were tandem repeat on chromosomes 4 and 8. There were 13 intron distribution patterns among the <i>CmbHLH</i> genes. Phylogenetic analysis illustrated that these CmbHLHs could be classified into 16 subfamilies. Expression patterns of the <i>CmbHLH</i> genes were studied using transcriptome data. Tissue specific expression of the <i>CmbHLH32</i> gene was analysed by quantitative RT-PCR. The results showed that the <i>CmbHLH32</i> gene was highly expressed in female flower and early developmental stage fruit. Transgenic melon lines overexpressing <i>CmbHLH32</i> were generated, and overexpression of <i>CmbHLH32</i> resulted in early fruit ripening compared to wild type. The <i>CmbHLH</i> transcription factor family was identified and analysed for the first time in melon, and overexpression of <i>CmbHLH32</i> affected the ripening time of melon fruit. These findings laid a foundation for further study on the role of bHLH family members in the growth and development of melon.
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