Sucrose rather than GA transported by AtSWEET13 and AtSWEET14 supports pollen fitness at late anther development stages

Summary Both sugar and hormone gibberellin (GA) are essential for anther-enclosed pollen development and thus for plant productivity in flowering plants. Arabidopsis (Arabidopsis thaliana) AtSWEET13 and AtSWEET14, which are expressed in anthers and associated with seed yield, transport both sucrose and GA. However, it is still unclear which substrate transported by them directly affects anther development and seed yield. Histochemical staining, cross-sectioning and microscopy imaging techniques were used to investigate and interpret the phenotypes of AtSWEET13 and AtSWEET14 double mutant during anther development. Genetic complementation of atsweet13;14 using AtSWEET9 that transports sucrose but not GA was conducted to test the substrate preference relevant to the biological process. The loss of AtSWEET13 and AtSWEET14 resulted in reduced pollen viability and therefore decreased pollen germination. AtSWEET9 fully rescued the defects in pollen fertility of atsweet13;14, indicating AtSWEET13/14 mediated sucrose rather than GA is essential to pollen fertility. AtSWEET13 and AtSWEET14 mainly function at the anther wall during late anther development stages and are likely responsible for sucrose efflux into locules to support pollen development to maturation, which is vital for subsequent pollen viability and germination.