Sugar beet cold-induced PMT5a and STP13 carriers are poised for taproot proton-driven plasma membrane sucrose and glucose import
Résumé
• As the major sugar-producing crop in the northern hemisphere, sugar beet taproots store sucrose at a concentration of about 20 %. While the vacuolar sucrose loader TST has already been identified in the taproot, sugar transporters mediating sucrose uptake across the plasma membrane of taproot parenchyma cells remained unknown.
• We electrophysiologically examined taproots for proton-coupled sugar uptake and identified potentially involved transporters by transcriptomic profiling. After cloning, the transporter features were studied in the heterologous Xenopus laevis oocyte expression system using the two-electrode voltage clamp technique. Insights into the structure were
gained by 3D homology modeling.
• As with glucose, sucrose stimulation of taproot parenchyma cells caused inward H+-fluxes and plasma membrane depolarization, indicating a sugar/proton symport mechanism. As one potential candidate for sugar uploading, the BvPMT5a was characterized as a H+-driven low-affinity glucose transporter, which does not transport sucrose. BvSTP13 operated as a high-affinity H+/sugar symporter, transporting glucose and to some extent sucrose due to a binding cleft plasticity. Both transporter genes were upregulated upon cold exposure, with the transport capacity of BvSTP13 being more cold-resistant than BvPMT5a.
• Identification of BvPMT5a and BvSTP13 as taproot sugar transporters could improve 43 breeding of cold-tolerant sugar beet to provide a sustainable energy crop.
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Licence : CC BY - Paternité
Licence : CC BY - Paternité