Plant sucrose transporters are required for phloem loading, and therefore are essential for plant growth and development. In common beans (Phaseolus vulgaris) 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 K_m 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, PvSUT1.1 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.

中文翻译：

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菜豆 SUT1.1 是一种高亲和力的蔗糖-质子协同转运蛋白。


植物蔗糖转运蛋白是韧皮部装载所必需的，因此对于植物生长和发育至关重要。在普通豆类（菜豆）中，只有两种蔗糖转运蛋白具有功能特征。通过之前的 RNA 测序研究，我们在菜豆中发现了一种假定的蔗糖转运蛋白，我们假设它在将蔗糖输入植物细胞中发挥作用。计算机分析显示，PvSUT1.1 是一种假定的蔗糖质子协同转运蛋白，与普通豆类中其他特征性的蔗糖转运蛋白不同，表明这是豆类中以前未描述过的转运蛋白。进一步分析发现，PvSUT1.1与韧皮部装载者拟南芥SUC2具有较高的蛋白质序列同源性；两者都具有 12 个跨膜结构域，这是植物蔗糖转运蛋白的典型特征。酵母中的异源表达进一步表明 PvSUT1.1 具有功能性，它将蔗糖导入酵母细胞中， K _m为 0.7 mM 蔗糖。通过 PvSUT1.1 导入蔗糖也依赖于 pH 值，在 pH 4.0 时吸收量最高，并且在解偶联剂羰基氰化物 3-氯苯腙存在时活性会丧失。与 PvSUT1.1 作为 I 型转运蛋白的鉴定一致，PvSUT1.1 还转运七叶苷。最后， PvSUT1.1在多个组织中显示表达，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，可能参与源细胞和库细胞对蔗糖的摄取。进一步讨论了 PvSUT1.1 在普通豆类叶韧皮部蔗糖负荷中的潜在作用及其在生殖组织耐热性中的重要性。