Salt stress is one of the major factors impacting crop productivity worldwide. Through a variety of effector and signaling pathways, plants achieve survival under salinity stress by maintaining high cytosolic potassium/sodium ion (K⁺/Na⁺) ratios, preventing Na⁺ cytotoxicity, and retaining osmotic balance. Ras‐related protein 5 (Rab5) members are involved in the trafficking of endosomes to the vacuole or plasma membrane (PM). The vacuolar protein sorting‐ associated protein 9 (vps9a) encodes the single guanine nucleotide exchange factor (GEF) that activates all three known Rab5 proteins in Arabidopsis thaliana. Previous work from our group has reported the critical function of vps9a for the operation of salt‐induced endocytic pathway, as well as the expansion of endomembrane compartments under saline stress conditions. Here we show an additional role of vps9a in plant response to salt stress via maintenance of K⁺ status of the cell rather than Na⁺ homeostasis. Our results show that roots from vps9a‐2 mutant, subjected to 100 mM NaCl, display alterations in transcript levels of genes involved in the K⁺ homeostasis pathway. Concurrent with the observed sensitivity of vps9a‐2 mutant under NaCl stress, exposure to low K⁺ environments resulted in growth retardation, and reduced rate of endocytosis. Furthermore, vps9a‐2 mutant displays reduced expression of auxin reporter, Direct Repeat‐5 (DR5), and alterations in polarity and abundance of auxin efflux carrier PIN‐ FORMED2 (PIN2). Imposition of NaCl stress was found to be restrictive to the elongation capacity of cells in the root elongation zone of vps9a‐2 mutant. Together our results indicate that alterations in K⁺ homeostasis and associated cellular changes causing increased cell wall pH, contribute to diminished root growth and compromised survival of vps9a‐2 mutant under salt stress conditions.

中文翻译：

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拟南芥RAB5 GEF vps9a在维持氯化钠胁迫下维持钾水平中的作用

盐胁迫是影响全球农作物生产力的主要因素之一。通过多种效应子和信号传导途径，植物可通过维持较高的胞质钾/钠离子（K ⁺ / Na ⁺）比，防止Na ⁺细胞毒性并保持渗透平衡来在盐胁迫下存活。Ras相关蛋白5（Rab5）成员参与将内体运输到液泡或质膜（PM）。液泡蛋白分选相关蛋白9（vps9a）编码单个鸟嘌呤核苷酸交换因子（GEF），该因子激活拟南芥中所有三种已知的Rab5蛋白。我们小组以前的工作已经报告了vps9a的关键功能用于盐诱导的内吞途径的运作，以及在盐胁迫条件下内膜隔室的扩展。在这里，我们通过维持细胞的K ⁺状态而不是Na ⁺稳态来显示vps9a在植物对盐胁迫的响应中的额外作用。我们的结果表明，vps9a-2突变体的根受到100 mM NaCl胁迫后，其参与K ⁺稳态途径的基因的转录水平发生了变化。与在NaCl胁迫下观察到的vps9a-2突变体的敏感性同时，暴露于低K ⁺环境导致生长迟缓和内吞率降低。此外，vps9a-2突变体显示出生长素报告基因，直接重复序列5（DR5）的表达降低，以及生长素外排载体PIN FORMED2（PIN2）的极性和丰度改变。发现施加NaCl胁迫限制了vps9a-2突变体根伸长区中细胞的伸长能力。我们的研究结果共同表明，在盐胁迫条件下，K ⁺稳态的改变和相关的细胞变化导致细胞壁pH值升高，导致根系生长减少，vps9a-2突变体的存活受到损害。