Santiago James P, Ward John M, Sharkey Thomas D
Plant Resilience Institute Michigan State University East Lansing MI USA.
Michigan State University-Department of Energy Plant Research Laboratory Michigan State University East Lansing MI USA.
Plant Direct. 2020 Aug 28;4(8):e00260. doi: 10.1002/pld3.260. eCollection 2020 Aug.
Plant sucrose transporters are required for phloem loading, and therefore are essential for plant growth and development. In common beans () there are only two sucrose transporters functionally characterized. Through a previous RNA-seq study, we identified a putative sucrose transporter in common bean, which we hypothesize to function in import of sucrose into plant cells. In silico analysis revealed that PvSUT1.1 is a putative sucrose-proton co-transporter distinct from other characterized sucrose transporters in common bean indicating that this is a previously undescribed transporter protein in beans. Further analysis revealed that PvSUT1.1 shares high protein sequence homology to the phloem loader Arabidopsis SUC2; both have 12 transmembrane domains, a typical characteristic of plant sucrose transporters. Heterologous expression in yeast further showed PvSUT1.1 to be functional and it imported sucrose into yeast cells with a of 0.7 mM sucrose. Import of sucrose through PvSUT1.1 is also pH-dependent with highest uptake at pH 4.0, and activity is lost in the presence of the uncoupler carbonyl cyanide 3-chlorophenylhydrazone. Consistent with identification of PvSUT1.1 as a Type I transporter, PvSUT1.1 also transports esculin. Finally, showed expression in multiple tissues and the protein was localized to the plasma membrane. The results show that PvSUT1.1 is a sucrose transporter that is probably involved in the uptake of sucrose into source and sink cells. The potential role of PvSUT1.1 in leaf phloem loading of sucrose in common beans and its importance in heat tolerance of reproductive tissues are further discussed.
植物蔗糖转运蛋白是韧皮部装载所必需的，因此对植物的生长发育至关重要。在菜豆（ ）中，只有两种功能已明确的蔗糖转运蛋白。通过之前的RNA测序研究，我们在菜豆中鉴定出一种假定的蔗糖转运蛋白，我们推测它在蔗糖向植物细胞内的转运过程中发挥作用。电子分析表明，PvSUT1.1是一种假定的蔗糖-质子共转运蛋白，与菜豆中其他已明确的蔗糖转运蛋白不同，这表明它是菜豆中一种此前未被描述过的转运蛋白。进一步分析发现，PvSUT1.1与韧皮部装载蛋白拟南芥SUC2具有高度的蛋白质序列同源性；两者都有12个跨膜结构域，这是植物蔗糖转运蛋白的典型特征。在酵母中的异源表达进一步表明PvSUT1.1具有功能，它能以0.7 mM蔗糖的 将蔗糖导入酵母细胞。通过PvSUT1.1进行的蔗糖转运也依赖于pH值，在pH 4.0时摄取量最高，并且在解偶联剂羰基氰3-氯苯腙存在的情况下活性丧失。与PvSUT1.1作为I型转运蛋白的鉴定结果一致，PvSUT1.1也能转运七叶苷。最后， 显示其在多个组织中表达，并且该蛋白定位于质膜。结果表明，PvSUT1.1是一种蔗糖转运蛋白，可能参与蔗糖向源细胞和库细胞的摄取。我们进一步讨论了PvSUT1.1在菜豆叶片韧皮部蔗糖装载中的潜在作用及其在生殖组织耐热性中的重要性。
