State Key Laboratory of Plant Physiology and Biochemistry (SKLPPB), College of Biological Sciences, China Agricultural University, Beijing, China.
The Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of Education, College of Life Sciences, Shandong University, Qingdao, China.
EMBO Rep. 2020 Jun 4;21(6):e50164. doi: 10.15252/embr.202050164. Epub 2020 Apr 6.
Potassium (K) is essential for plant growth and development. Here, we show that the KUP/HAK/KT K transporter KUP9 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. KUP9 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 KUP9 affects auxin homeostasis in QC cells. Further studies showed that KUP9 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 KUP9 maintains Arabidopsis root meristem activity and root growth by regulating K and auxin homeostasis in response to low-K stress.
钾（K）是植物生长和发育所必需的。在这里，我们表明，KUP/HAK/KT 钾转运蛋白 KUP9 控制拟南芥的主根生长。在低钾条件下，kup9 突变体表现出短根表型，这是由于根细胞数量减少所致。KUP9 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 细胞用于维持根分生组织的活性，低钾条件诱导 kup9 突变体中的 QC 细胞分裂，导致根分生组织活性受损。外源生长素处理或特异性增加 QC 细胞中的生长素水平可以挽救 kup9 突变体的短根表型和增强的 QC 细胞分裂，表明 KUP9 影响 QC 细胞中的生长素稳态。进一步的研究表明，KUP9 主要定位于内质网（ER），在低钾条件下，它在 QC 细胞中从 ER 腔介导 K 和生长素向细胞质的外排。这些结果表明，KUP9 通过响应低钾胁迫调节 K 和生长素稳态来维持拟南芥根分生组织活性和根生长。
