Potassium (K) is essential for plant growth and development. Here, we show that the KUP /HAK /KT K⁺ transporter KUP 9 controls primary root growth in Arabidopsis thaliana . Under low‐K⁺ conditions, kup9 mutants displayed a short‐root phenotype that resulted from reduced numbers of root cells. KUP 9 was highly expressed in roots and specifically expressed in quiescent center (QC ) cells in root tips. The QC acts to maintain root meristem activity, and low‐K⁺ conditions induced QC cell division in kup9 mutants, resulting in impaired root meristem activity. The short‐root phenotype and enhanced QC cell division in kup9 mutants could be rescued by exogenous auxin treatment or by specifically increasing auxin levels in QC cells, suggesting that KUP 9 affects auxin homeostasis in QC cells. Further studies showed that KUP 9 mainly localized to the endoplasmic reticulum (ER ), where it mediated K⁺ and auxin efflux from the ER lumen to the cytoplasm in QC cells under low‐K⁺ conditions. These results demonstrate that KUP 9 maintains Arabidopsis root meristem activity and root growth by regulating K⁺ and auxin homeostasis in response to low‐K⁺ stress.

中文翻译：

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KUP9 通过调节 K+ 和生长素稳态以响应低 K 来维持根分生组织的活性。

钾 (K) 对植物的生长和发育至关重要。在这里，我们表明 KUP /HAK /KT K ^{+转运蛋白 KUP 9 控制}拟南芥的初级根生长。在低 K ⁺条件下，kup9突变体表现出由根细胞数量减少导致的短根表型。KUP 9在根中高度表达，并在根尖的静止中心 (QC) 细胞中特异性表达。QC 起到维持根分生组织活性的作用，低 K ⁺条件诱导kup9突变体中的 QC 细胞分裂，导致根分生组织活性受损。kup9中的短根表型和增强的 QC 细胞分裂突变体可以通过外源性生长素处理或通过特异性增加 QC 细胞中的生长素水平来挽救，这表明 KUP 9 影响 QC 细胞中的生长素稳态。进一步的研究表明，KUP 9 主要定位于内质网 (ER)，在低 K ⁺条件下，它在 QC 细胞中介导 K ^{+和生长素从 ER 腔流出到细胞质。}这些结果表明，KUP 9通过调节 K ⁺和生长素稳态以响应低 K ⁺胁迫，维持拟南芥根分生组织活性和根生长。