Genome-Wide Identification of SWEET Genes and Expression Dynamics of MrSWEET15 During Fruit Ripening in Chinese Bayberry (Morella rubra)

Sugar transporters of the SWEET family play a crucial role in sugar partitioning and fruit quality, yet their functions remain uncharacterized in Chinese bayberry (Morella rubra). In this study, we present the first genome-wide identification and characterization of the SWEET gene family in species, revealing 15 MrSWEET genes distributed across eight chromosomes. Phylogenetic analysis classified these genes into four conserved clades with distinct tissue-specific expression patterns. During fruit ripening, transcripts of MrSWEET1, 2b, 4, and 15 accumulated progressively, with MrSWEET15 showing the strongest increase. Weighted gene co-expression network analysis (WGCNA) identified a “lightcyan” module that correlates strongly with fruit sugar content (r > 0.8) and contains MrSWEET15, three additional MrSWEET genes, and 47 transcription factors (Dof, MYB, NAC, ERF, MADS, WRKY). Promoter analysis of MrSWEET15 revealed the presence of light- and hormone-responsive cis-elements (MYB, MYC, HY5, bZIP, and Dof), and MYB1, HY5, and Dof1.5 expression profiles are synchronized with MrSWEET15, suggesting potential regulatory relationships. These findings establish MrSWEET15 as a priority candidate for sugar transport in Chinese bayberry and our understanding of the molecular basis of sugar transport and fruit quality formation.