Institute of Transformative Bio-Molecules, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Proc Natl Acad Sci U S A. 2022 Oct 18;119(42):e2207558119. doi: 10.1073/pnas.2207558119. Epub 2022 Oct 10.
SWEET sucrose transporters play important roles in the allocation of sucrose in plants. Some SWEETs were shown to also mediate transport of the plant growth regulator gibberellin (GA). The close physiological relationship between sucrose and GA raised the questions of whether there is a functional connection and whether one or both of the substrates are physiologically relevant. To dissect these two activities, molecular dynamics were used to map the binding sites of sucrose and GA in the pore of SWEET13 and predicted binding interactions that might be selective for sucrose or GA. Transport assays confirmed these predictions. In transport assays, the N76Q mutant had 7x higher relative GA activity, and the S142N mutant only transported sucrose. The impaired pollen viability and germination in double mutants were complemented by the sucrose-selective SWEET13, but not by the SWEET13 mutant, indicating that sucrose is the physiologically relevant substrate and that GA transport capacity is dispensable in the context of male fertility. Therefore, GA supplementation to counter male sterility may act indirectly via stimulating sucrose supply in male sterile mutants. These findings are also relevant in the context of the role of SWEETs in pathogen susceptibility.
蔗糖转运蛋白 SWEET 在植物中蔗糖的分配中发挥重要作用。一些 SWEET 被证明也介导植物生长调节剂赤霉素（GA）的运输。蔗糖和 GA 之间密切的生理关系提出了这样的问题，即是否存在功能联系，以及一种或两种底物是否具有生理相关性。为了解剖这两种活性，使用分子动力学来绘制 SWEET13 孔中蔗糖和 GA 的结合位点，并预测可能对蔗糖或 GA 具有选择性的结合相互作用。转运实验证实了这些预测。在转运实验中，N76Q 突变体对 GA 的相对活性高 7 倍，而 S142N 突变体只运输蔗糖。双突变体中花粉活力和萌发受损可被蔗糖选择性 SWEET13 互补，但不能被 SWEET13 突变体互补，表明蔗糖是生理相关的底物，而在雄性育性的背景下，GA 运输能力是可有可无的。因此，GA 补充剂可能通过刺激雄性不育突变体中蔗糖的供应来间接对抗雄性不育。这些发现对于 SWEET 在病原体易感性中的作用也具有相关性。
