Cytokinin plays an important role in plant stress responses via a multistep signaling pathway, involving the histidine phosphotransfer proteins (HPs). In Arabidopsis thaliana, the AHP2, AHP3 and AHP5 proteins are known to impact drought responses; however, the role of AHP4 in drought adaptation remains undetermined. In the present study, using a loss-of-function approach we showed that AHP4 possesses a negative regulatory role in Arabidopsis response to drought. This is evidenced by both higher survival rates of ahp4 than wild-type (WT) plants under drought conditions, and the down-regulated AHP4 expression in WT during periods of dehydration. Comparative transcriptome analysis of ahp4 and WT plants revealed AHP4-mediated expression of several dehydration- and/or abscisic acid (ABA)-responsive genes involved in regulation of various physiological and biochemical processes important for plant drought acclimation. In comparison with WT, ahp4 plants showed increased wax crystal accumulation in stems, thicker cuticles in leaves, greater sensitivity to exogenous ABA at germination, narrow stomatal apertures, heightened leaf temperatures during dehydration, and longer root length under osmotic stress. Additionally, ahp4 plants showed greater photosynthetic efficiency, lower levels of reactive oxygen species (ROS), reduced electrolyte leakage and lipid peroxidation, and increased anthocyanin contents under drought, when compared with WT. These differences displayed in ahp4 plants are likely due to up-regulation of genes that encode enzymes involved in ROS-scavenging and non-enzymatic antioxidant metabolism. The role of AHP4 in negative regulation of multiple protective mechanisms associated with drought tolerance could make editing of AHP4 a promising approach for the production of drought-tolerant crop plants.

中文翻译：

---

组氨酸磷酸转移AHP4在拟南芥植物对干旱的响应中起负作用

细胞分裂素通过涉及组氨酸磷酸转移蛋白（HPs）的多步信号通路在植物胁迫反应中起重要作用。在拟南芥中，已知AHP2，AHP3和AHP5蛋白会影响干旱响应。但是，AHP4在干旱适应中的作用尚未确定。在本研究中，我们使用功能丧失方法表明，AHP4在拟南芥对干旱的响应中具有负调控作用。干旱条件下ahp4的存活率高于野生型（WT）植物，并且脱水期间WT中的AHP4表达下调，这证明了这一点。对ahp4和WT植物进行的转录组比较分析显示，AHP4介导了几种脱水和/或脱落酸（ABA）响应基因的表达，这些基因参与调节对植物干旱适应重要的各种生理和生化过程。与野生型相比，ahp4植物在茎中的蜡晶积累增加，叶片中的表皮变厚，发芽时对外源ABA的敏感性更高，气孔孔径变窄，脱水过程中叶片温度升高，在渗透胁迫下根系长度更长。此外，与野生型相比，ahp4植物在干旱条件下显示出更高的光合作用效率，较低的活性氧（ROS）水平，减少的电解质泄漏和脂质过氧化作用以及花色苷含量增加。在ahp4植物中显示出的这些差异可能是由于编码与ROS清除和非酶抗氧化剂代谢有关的酶的基因上调所致。AHP4在与耐旱性相关的多种保护机制的负调控中的作用可能使AHP4的编辑成为生产耐旱作物的有前途的方法。