Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute, Biocenter, Julius-Maximilians-Universität Würzburg, Würzburg, 97082, Germany.
Institute of Education and Student Affairs, University of Münster, Münster, Germany.
Nat Commun. 2024 Oct 3;15(1):8558. doi: 10.1038/s41467-024-52963-6.
Plants can survive in soils of low micromolar potassium (K) concentrations. Root K intake is accomplished by the K channel AKT1 and KUP/HAK/KT type high-affinity K transporters. Arabidopsis HAK5 mutants impaired in low K acquisition have been identified already more than two decades ago, the molecular mechanism, however, is still a matter of debate also because of lack of direct measurements of HAK5-mediated K currents. When we expressed AtHAK5 in Xenopus oocytes together with CBL1/CIPK23, no inward currents were elicited in sufficient K media. Under low K and inward-directed proton motive force (PMF), the inward K current increased indicating that HAK5 energetically couples the uphill transport of K to the downhill flux of H. At extracellular K concentrations above 25 μM, the initial rise in current was followed by a concentration-graded inactivation. When we replaced Tyr450 in AtHAK5 to Ala the K affinity strongly decreased, indicating that AtHAK5 position Y450 holds a key for K sensing and transport. When the soil K concentration drops toward the range that thermodynamically cannot be covered by AKT1, the AtHAK5 K/H symporter progressively takes over K nutrition. Therefore, optimizing K use efficiency of crops, HAK5 could be key for low K tolerant agriculture.
植物可以在低毫摩尔浓度的钾（K）土壤中生存。根 K 的摄取是通过 K 通道 AKT1 和 KUP/HAK/KT 型高亲和力 K 转运体来完成的。二十多年前，已经鉴定出拟南芥 HAK5 突变体在低 K 摄取方面受损，然而，其分子机制仍然存在争议，这也是由于缺乏对 HAK5 介导的 K 电流的直接测量。当我们将 AtHAK5 与 CBL1/CIPK23 在非洲爪蟾卵母细胞中表达时，在足够的 K 介质中没有诱发内向电流。在低 K 和内向质子动力势（PMF）下，内向 K 电流增加，表明 HAK5 在能量上使 K 的向上运输与 H 的向下流动偶联。当细胞外 K 浓度高于 25 μM 时，电流的初始上升后会发生浓度分级失活。当我们将 AtHAK5 中的 Tyr450 突变为 Ala 时，K 的亲和力大大降低，表明 AtHAK5 的位置 Y450 对于 K 的感应和运输起着关键作用。当土壤 K 浓度下降到 AKT1 无法覆盖的热力学范围时，AtHAK5 的 K/H 同向转运体逐渐接管 K 营养。因此，优化作物的 K 使用效率，HAK5 可能是低 K 耐受农业的关键。
