KUP9 maintains root meristem activity by regulating K+ and auxin homeostasis in response to low K

• Published in: EMBO reports 2020-06, Vol.21 (6), p.e50164-n/a
• Main Authors: Zhang, Mei‐Ling, Huang, Pan‐Pan, Ji, Yun, Wang, Shuwei, Wang, Shao‐Shuai, Li, Zhen, Guo, Yan, Ding, Zhaojun, Wu, Wei‐Hua, Wang, Yi
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; auxin transport; Cell division; Cytoplasm; Efflux; EMBO11; EMBO20; EMBO30; Endoplasmic reticulum; Gene Expression Regulation, Plant; Homeostasis; Indoleacetic Acids; KUP9; low‐K+ stress; Meristem - growth & development; meristem cell; Meristems; Mutants; Phenotypes; Plant growth; Plant Roots - growth & development; Potassium; root growth; Roots; Tips
• ISSN: 1469-221X; 1469-3178
• DOI: 10.15252/embr.202050164

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. Synopsis The ER‐localized transporter KUP9 regulates K + and auxin homeostasis in Arabidopsis quiescent center (QC) cells in response to low‐K + stress, thus regulating meristem activity and primary root growth. The K + transporter KUP9 maintains root meristem activity and primary root growth in Arabidopsis under conditions of low‐K + stress by regulating auxin homeostasis in root tips. KUP9 is highly expressed in roots, and specifically expressed in quiescent center (QC) cells in root tips. KUP9 targets to the ER membrane and mediates auxin and K + transport from the ER lumen to the cytoplasm in the QC cells under low‐K + conditions. Graphical Abstract The ER‐localized transporter KUP9 regulates K + and auxin homeostasis in Arabidopsis quiescent center (QC) cells in response to low‐K + stress, thus regulating meristem activity and primary root growth.