背景回顾：Excessive accumulation of chloride (Cl-) in the aboveground tissues under saline (NaCl) conditions is harmful to crops. Increasing the exclusion of Cl- from shoots promotes salt tolerance in various crops. 

提出问题：However, the underlying molecular mechanisms remain largely unknown. 

主要发现：Here, we demonstrate that a type-A response regulator (ZmRR1) confers a natural variation of maize salt tolerance by modulating Cl- exclusion from shoots. 

结果1-ZmRR1-ZmHP2：ZmRR1 negatively regulates cytokinin signaling and salt tolerance, likely by interacting with and inhibiting His phosphotransfer (HP) proteins (key mediators of cytokinin signaling). A naturally occurring non-synonymous SNP variant enhances the interaction between ZmRR1 and ZmHP2, yielding a salt-hypersensitive phenotype. ZmRR1 undergoes degradation under saline conditions, leading to the release of ZmHP2 from ZmRR1 inhibition, and subsequently ZmHP2-mediated signaling improves salt tolerance primarily by promoting Cl- exclusion from shoots. 

结果2-ZmHP2-CK信号-ZmMATE29-氯离子外排：Next, we showed that ZmMATE29 is transcriptionally upregulated by ZmHP2-mediated signaling under highly saline conditions and encodes a tonoplast-located Cl- transporter that promotes Cl- exclusion from shoots by compartmentalizing Cl- into the vacuoles of root cortex cells. 

结论：Our study provides an important mechanistic understanding of the cytokinin signaling-mediated promotion of Cl- exclusion from shoots and salt tolerance. Therefore, genetic modification to promote Cl- exclusion from shoots is a promising route for developing salt-tolerant maize.

盐胁迫条件下作物地上部过量积累氯离子会对生长造成损伤。通过减少地上部中的氯离子含量，能够增强作物对盐胁迫的耐受性。但是，潜在的分子机制仍不清楚。本文中，作者发现A类响应调控子ZmRR1通过调控玉米地上部对氯离子的排斥，赋予了玉米耐盐性自然变异。ZmRR1可能是通过与His磷酸传递蛋白HP互作，抑制其酶活，从而负调控细胞分裂素信号转导和盐耐受性。一个非同义SNP变异导致了ZmRR1能够与ZmHP2互作，从而产生了一个盐超敏表型。ZmRR1会在盐胁迫条件下会被降解，从而解除ZmRR1对ZmHP2的抑制效果，继而通过ZmHP2介导信号转导促进地上部对氯离子的排斥，最终增强盐耐受性。接着，作者发现盐胁迫条件下，ZmMATE29受到ZmHP2介导的信号转导的转录上调，该基因编码一个具有液泡膜定位的氯离子转运蛋白，通过将氯离子隔离在根皮层细胞的液泡中，从而减少向地上部的转运。本文的研究揭示了一个由细胞分裂素信号转导介导的植物地上部减少氯离子积累和盐耐受性调控机制。因此，未来有望通过遗传修饰促进玉米地上部的氯离子外排，来开发耐盐玉米品种。

** 蒋才富 **