Genomic Expansion and Subgenome Expression Divergence of Sugar Transporters During Polyploid Evolution of Bamboos

Sugar transporters play a pivotal role in photoassimilate partitioning and biomass accumulation in plants. However, how whole-genome duplication (WGD) has reshaped the evolutionary trajectory of the sugar transport system in Bambusoideae remains elusive. Here, we systematically identified and characterized the SUT (Sucrose Transporters) and MST (Monosaccharide Transporters) gene families across 14 bamboo genomes representing four major lineages: herbaceous, temperate woody, neotropical woody and paleotropical woody bamboos. Our results suggest that WGD acted as the primary driving force behind the expansion of these gene families, with woody bamboos possessing significantly higher gene counts than herbaceous bamboos. Notably, extensive gene loss was observed in hexaploid lineages, aligning with the gene dosage balance hypothesis. Phylogenetic and sequence analyses demonstrated that core genes were subjected to purifying selection. Intriguingly, 21 groups of identical protein sequences across species were identified in paleotropical woody bamboos, suggesting high sequence conservation. Transcriptomic and syntenic analyses further unveiled the mechanisms of post-polyploidization expression divergence: homeologs exhibited marked expression asymmetry across subgenomes. Distinct from the broad expression pattern in herbaceous bamboos, which rely on SUT5 and a few STP (Sugar Transporter Protein) genes, woody bamboos have achieved fine-tuned expression partitioning and tissue-specific specialization during different culm developmental stages through significantly expanded SUT and STP family members. This study reveals an evolutionary pattern characterized by "WGD-driven expansion, post-polyploid fractionation, and subgenome expression divergence." This pattern suggests a potential link to the enhanced sugar allocation efficiency required for the explosive growth of woody bamboos, offering valuable gene resources and a foundation for future functional studies in Poaceae crops.