Abstract
Litchi is an important subtropical fruit, highly valued by consumers for its vibrant color and distinctive flavor. B-box (BBX) proteins, which are zinc finger transcription factors, play a crucial role in regulating plant growth, development, and stress responses. Nevertheless, the specific function of BBX genes in the development and coloration of litchi fruit remains inadequately understood. In this study, 21 LcBBX genes (designated as LcBBX1-LcBBX21) were identified within the litchi genome. These genes were categorized into five sub-families based on phylogenetic analysis and were found to be unevenly distributed across 12 chromosomes. Promoter analysis revealed a rich presence of light-responsive elements, such as the G-box, and abscisic acid (ABA) responsive elements, including ABRE, within the promoter regions of LcBBX genes. Protein-protein interaction predictions indicated that the majority of LcBBX genes have the potential to interact with the light-responsive factor HY5. Transcriptome analysis and qRT-PCR results demonstrated that LcBBX genes exhibit tissue-specific expression patterns. Notably, most LcBBX genes were highly expressed prior to fruit coloration, whereas LcBBX4 and LcBBX10 were upregulated during the fruit coloration phase. Furthermore, LcBBX1/4/6/7/15/19 were upregulated in response to light following the removal of shading. The findings suggest that LcBBX4 may directly regulate anthocyanin biosynthesis in litchi pericarp. This study provides critical insights into the molecular mechanisms underlying litchi fruit development and coloration.