Characterization and functional divergence of genes encoding sucrose transporters in oilseeds castor bean

Castor bean (Ricinus communis L.) is an economically important non-edible oilseed crop. Its seed oils are rich in hydroxy fatty acid, which are highly valuable with a wide range of industrial applications. Sucrose transportation is critical in regulating the growth, development and oilseed yield in castor bean. The transporters or carriers (SUTs or SUCs) play a central role in orchestrating sucrose allocation and aiding in plant adaptation to diverse stresses. In this study, based on castor bean genome, three RcSUCs (RcSUC2, RcSUC3 and RcSUC4) were identified and characterized. The expressional profiles of RcSUCs in different tissues such as leaf, stem, root, phloem and seed tissues exhibited a distinct divergence of gene expression, suggesting that the functions of RcSUC2, RcSUC3 and RcSUC4 are differentiated into long or short-distance transportation among tissues. Additionally, under abiotic stresses including hot temperature, low temperature, drought and salt stresses, the sugar allocation among leaf, stem and roots was tested. The expressional changes of RcSUCs in leaf, stem and root tissues were associated with sugar transportation and allocation. Taken together, the differential expression of RcSUCs among tissues responsing to abiotic stress suggested functional differences in sucrose transport and redistribution in different tissues. This study is helpful to understand the physiological and molecular mechanisms of sucrose transportation and allocation among tissues in heterotrophic oilseeds, and could provide clues for genetic improvement and optimization of cultivation practices.