Genome-Wide Identification of the Litchi BBX Gene Family and Analysis of Its Potential Role in Pericarp Coloring

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 <i>BBX</i> genes in the development and coloration of litchi fruit remains inadequately understood. In this study, 21 <i>LcBBX</i> genes (designated as <i>LcBBX1</i>-<i>LcBBX21</i>) 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 <i>LcBBX</i> genes. Protein-protein interaction predictions indicated that the majority of <i>LcBBX</i> genes have the potential to interact with the light-responsive factor HY5. Transcriptome analysis and qRT-PCR results demonstrated that <i>LcBBX</i> genes exhibit tissue-specific expression patterns. Notably, most <i>LcBBX</i> genes were highly expressed prior to fruit coloration, whereas <i>LcBBX4</i> and <i>LcBBX10</i> were upregulated during the fruit coloration phase. Furthermore, <i>LcBBX1</i>/<i>4</i>/<i>6</i>/<i>7</i>/<i>15</i>/<i>19</i> were upregulated in response to light following the removal of shading. The findings suggest that <i>LcBBX4</i> may directly regulate anthocyanin biosynthesis in litchi pericarp. This study provides critical insights into the molecular mechanisms underlying litchi fruit development and coloration.