ABA-Induced Sugar Transporter TaSTP6 Promotes Wheat Susceptibility to Stripe Rust.

Biotrophic pathogens, such as wheat rust fungi, survive on nutrients derived from host cells. Sugar appears to be the major carbon source transferred from host cells to various fungal pathogens; however, the molecular mechanism by which host sugar transporters are manipulated by fungal pathogens for nutrient uptake is poorly understood. TaSTP6, a sugar transporter protein in wheat (), was previously shown to exhibit enhanced expression in leaves upon infection by f. sp. (), the causal agent of wheat stripe rust. In this study, we found that infection caused increased accumulation of abscisic acid (ABA) and that application of exogenous ABA significantly enhanced expression. Moreover, knockdown of expression by barley stripe mosaic virus-induced gene silencing reduced wheat susceptibility to the pathotype CYR31, suggesting that expression upregulation contributes to host sugar acquisition. Consistent with this, overexpression in Arabidopsis () promoted plant susceptibility to powdery mildew and led to increased Glc accumulation in the leaves. Functional complementation assays in showed that TaSTP6 has broad substrate specificity, indicating that TaSTP6 is an active sugar transporter. Subcellular localization analysis indicated that TaSTP6 localizes to the plasma membrane. Yeast two-hybrid and bimolecular fluorescence complementation experiments revealed that TaSTP6 undergoes oligomerization. Taken together, our results suggest that stimulates ABA biosynthesis in host cells and thereby upregulates expression, which increases sugar supply and promotes fungal infection.