Phaseolus vulgaris SUT1.1 is a high affinity sucrose‐proton co‐transporter

Abstract

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 Km 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.

Contrasting anther glucose‐6‐phosphate dehydrogenase activities between two bean varieties suggest an important role in reproductive heat tolerance

“…The expression of a sucrose transporter gene hypothesized to be involved in phloem loading of sucrose (Santiago, Ward, & Sharkey, 2020 ; Soltani et al, 2019 ) was measured by qRT‐PCR in both heat‐sensitive and heat‐tolerant genotypes. The expression of PvSUT1.1 was significantly reduced at high temperature in both bean varieties (Figure 4d ; Figure S1 ).…”

The Tiny Companion Matters: The Important Role of Protons in Active Transports in Plants

“…The Phaseolus vulgaris SUT1.1, when expressed in transgenic yeast, was found to have a higher transport activity when the pH of the medium was more acidic [ 84 ]. The tonoplast- and plasma membrane-localized PvSUT1.1 was reported to be a sucrose-proton co-transporter that is probably involved in the export of sucrose from the leaf through the phloem [ 84 ]. In the same study, the expression of PvSUT1.1 was found to be repressed in the leaf upon heat stress [ 84 ].…”

“…The tonoplast- and plasma membrane-localized PvSUT1.1 was reported to be a sucrose-proton co-transporter that is probably involved in the export of sucrose from the leaf through the phloem [ 84 ]. In the same study, the expression of PvSUT1.1 was found to be repressed in the leaf upon heat stress [ 84 ]. Since the export of sucrose from the leaf is important for heat tolerance, the heat stress susceptibility of P. vulgaris was therefore hypothesized to be associated with the repression of PvSUT1.1 under high temperature [ 84 ].…”

“…In the same study, the expression of PvSUT1.1 was found to be repressed in the leaf upon heat stress [ 84 ]. Since the export of sucrose from the leaf is important for heat tolerance, the heat stress susceptibility of P. vulgaris was therefore hypothesized to be associated with the repression of PvSUT1.1 under high temperature [ 84 ]. However, under high temperature in the leaf, H + can leak through membranes [ 85 ].…”

Regulation of Cytosolic pH: The Contributions of Plant Plasma Membrane H+-ATPases and Multiple Transporters

“…Third, the matter of how these proteins cooperate to achieve cytosolic pH homeostasis awaits further study [ 178 ]. Additionally, except for the seven types of protein, transporters such as H + -coupled su crose t ransporters (abbreviated as SUT), H + -coupled a mino a cid p ermease (abbreviated as AAP), and sul fate tr ansporters (abbreviated as SULTR) are also conceived to contribute to the cytosolic pH through direct mediating H + flux across the plasma membrane [ 8 , 179 , 180 , 181 , 182 ]. Studies on these proteins, and the coordination of these plasma membrane H + transport proteins, in addition to organelle-located ones, are crucial for the elucidation of the molecular mechanism for cytosolic pH homeostasis.…”