Genome-wide identification, characterization and expression profile analysis of BBX gene family in Chinese chestnut (Castanea mollissima)

The B-box (BBX) proteins are a class of zinc finger transcription factors and play critical roles in plant development and growth. However, they have not been systematically characterized in Chinese chestnut ( Castanea mollissima ), an important nut with rich nutrition and high economic value. Here, 18 BBX genes were identified in Chinese chestnut genome and divided into five groups through phylogenetic analysis, with members in the same group containing the same conserved domain organization. The collinearity analysis showed that dispersed duplication played a major role in the expansion of CmBBX gene family inferred to have evolved through purifying selection. Transcriptome analysis and qRT-PCR experiments suggested that CmBBX genes showed different expression patterns in different Chinese chestnut tissues, and revealed some CmBBXs may have potential functions in the development of Chinese chestnut buds, nuts, fertile/abortive ovules. Combined with the analysis of conserved domain, motif, cis -elements, expression level and protein three-dimensional structure, the lack of cis -acting elements related to meristem expression and gibberellin-responsiveness may lead to the no-expression of CmBBX9 in Chinese chestnut. The systematic analysis of Chinese chestnut BBX genes provides a basis for further understanding the characteristics and potential functions of BBX gene family.