Genomic Analyses of SUT and TST Sugar Transporter Families in Low and High Sugar Accumulating Sugarcane Species ( Saccharum spontaneum and Saccharum officinarum )

Sugarcane ( Saccharum spp.) is an economically vital crop that is a primary source of sugar in our food and is also used for ethanol production. Various studies have been performed to understand the molecular mechanisms underlying sugar accumulation in sugarcane, but the complex, polyploid genome has posed many challenges. Here, we analyzed the recently sequenced genomes of two sugarcane varieties: Saccharum spontaneum , a geographically widespread, stress tolerant, and low sugar-accumulating wild relative of domesticated sugarcane, and Saccharum officinarum , a high sugar-accumulating variety, to investigate the composition and roles of two sugar transporter protein families, Sucrose Transporters (SUTs) and Tonoplast Sugar Transporters (TSTs). We found an increase in the number of alleles for various SUT and TST genes in S. officinarum and S. spontaneum compared to sorghum and other grass species , and we identified new putative TST genes previously uncharacterized . We analyzed expression levels of these genes in various tissues at different stages and identified SUTs and TSTs likely involved in sugar transport and storage. We hypothesize that these sugar transporter genes in S. officinarum , particularly TSTs , contribute to the ability of modern sugarcane hybrid varieties to accumulate large amounts of sugar in the stem.