Genome-Wide Identification and Characterization of the UMAMIT Gene Family in Brassica napus: Evolution, Expression, and Potential Association with Oil Content

The UMAMIT (Usually Multiple Acids Move In and Out Transporters) family comprises plant-specific amino acid transporters that play key roles in nitrogen uptake, transport, and storage. As a major oil crop in the Brassicaceae family, efficient amino acid transport in Brassica napus seeds is closely linked to seed yield and quality. Despite extensive studies in other species, the UMAMIT gene family has not been systematically characterized in B. napus. In this study, we identified 172 BnaUMAMIT genes, all of which harbor the EamA/WAT1-related domain and are predicted to localize to the plasma membrane. Both tandem and whole-genome/segmental duplications contributed to the expansion of this gene family. Phylogenetic analysis clustered BnaUMAMIT proteins into eight clades, revealing extensive collinearity with homologs in Arabidopsis thaliana, Brassica rapa, and Brassica oleracea. Gene structure analysis revealed conserved exon–intron organization within subgroups, whereas promoter analysis revealed diverse cis-acting elements associated with stress responses, hormone signaling, and developmental regulation. Transcriptome profiling revealed that 6 BnaUMAMIT genes were more highly expressed in low-oil-content seeds than in high-oil-content seeds at 25, 35, and 45 days after pollination in the two different environments, suggesting a possible association with seed oil content. Weighted gene co-expression network analysis (WGCNA) further demonstrated a significant correlative relationship between BnaUMAMIT transcripts and seed oil accumulation; meanwhile, co-expression network analysis revealed that BnaUMAMITs are correlated with the expression of lipid synthesis-related transcription factors, such as BnaTT8, BnaSTK, BnaGL2, BnaLEC1, and BnaLEC2, suggesting a potential regulatory association involved in seed oil accumulation. However, these results remain correlative and require further functional validation. Taken together, the results of this study provide a comprehensive understanding of the evolution, structure, and expression of the BnaUMAMIT gene family, laying a foundation for future functional studies and potential improvements in seed oil content in B. napus.