Under phosphorus (P) deficiency, Lupinus albus (white lupin) releases large amounts of organic acid anions from specialized root structures, so‐called cluster or proteoid roots, to mobilize and acquire sparingly soluble phosphates from a restricted soil volume. The molecular mechanisms underlying this release and its regulation are, however, poorly understood. Here, we identified a gene belonging to the aluminium (Al)‐activated malate transporter (ALMT) family that specifically contributes to malate, but not citrate release. This gene, LaALMT1 , was most prominently expressed in the root apices under P deficiency, including those of cluster roots and was also detected in the root stele. Contrary to several ALMT homologs in other species, the expression was not stimulated, but moderately repressed by Al. Aluminium‐independent malate currents were recorded from the plasma membrane localized LaALMT1 expressed in Xenopus oocytes. In composite lupins with transgenic roots, LaALMT1 was efficiently mutated by CRISPR‐Cas9, leading to diminished malate efflux and lower xylem sap malate concentrations. When grown in an alkaline P‐deficient soil, mutant shoot phosphate concentrations were similar, but iron and potassium concentrations were diminished in old leaves, suggesting a role for ALMT1 in metal root to shoot translocation, a function that was also supported by growth in hydroponics.

中文翻译：

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LaALMT1介导苹果酸从缺磷的白羽扇豆根尖和金属根的释放释放到芽。

在缺乏磷（P）的情况下，白羽扇豆（Lupinus albus（white lupin））从特殊的根系结构（所谓的簇状或蛋白状根）中释放出大量有机酸阴离子，以从有限的土壤体积中动员并获得微溶的磷酸盐。然而，对该释放及其调控的分子机制了解甚少。在这里，我们确定了一个基因，该基因属于铝（Al）活化的苹果酸转运蛋白（ALMT）家族，专门促进苹果酸的释放，但不促进柠檬酸的释放。这个基因，LaALMT1在缺磷条件下的根尖中最显着表达，包括簇状根，并且在根碑中也检测到。与其他物种的几个ALMT同源物相反，该表达不受Al刺激，但被Al适度抑制。从非洲爪蟾卵母细胞中表达的质膜定位的LaALMT1记录了不依赖于铝的苹果酸电流。在具有转基因根的复合羽扇豆中，LaALMT1被CRISPR‐Cas9有效突变，导致苹果酸外排减少，木质部汁液苹果酸浓度降低。在碱性缺磷的土壤中生长时，突变芽的磷酸盐浓度相似，但老叶中铁和钾的浓度降低，这表明ALMT1在金属根向芽易位中的作用，该功能也由水培法支持。