Genome-Wide Identification and Expression Analysis of the SBP-Box Gene Family in Loquat Fruit Development

The loquat ( L.) is a special evergreen tree, and its fruit is of high medical and health value as well as having stable market demand around the world. In recent years, research on the accumulation of nutrients in loquat fruit, such as carotenoids, flavonoids, and terpenoids, has become a hotspot. The SBP-box gene family encodes transcription factors involved in plant growth and development. However, there has been no report on the SBP-box gene family in the loquat genome and their functions in carotenoid biosynthesis and fruit ripening. In this study, we identified 28 genes in the loquat genome, which were unevenly distributed on 12 chromosomes. We also systematically investigated the phylogenetic relationship, collinearity, gene structure, conserved motifs, and -elements of EjSBP proteins. Most genes showed high expression in the root, stem, leaf, and inflorescence, while only five genes were highly expressed in the fruit. Gene expression analysis revealed eight differentially expressed genes between yellow- and white-fleshed fruits, suggesting that the genes play important roles in loquat fruit development at the breaker stage. Notably, and exhibited completely opposite expression patterns between white- and yellow-fleshed fruits during fruit development, and showed a close relationship with involved in carotenoid biosynthesis and fruit ripening, indicating that these two genes may participate in the synthesis and accumulation of carotenoids in loquat fruit. In summary, this study provides comprehensive information about the SBP-box gene family in the loquat, and identified two genes as candidates involved in carotenoid synthesis and accumulation during loquat fruit development.