Department of Bioenergy Science and Technology and Kumho Life Science Laboratory, Chonnam National University, Buk-Gu, Gwangju 500-757, Republic of Korea.
J Plant Physiol. 2012 Sep 15;169(14):1382-91. doi: 10.1016/j.jplph.2012.05.007. Epub 2012 Jun 15.
Cytokinin signaling in Arabidopsis thaliana utilizes a multi-step two-component signaling (TCS) system comprised of sensor histidine kinases (AHKs), histidine phosphotransfer proteins (AHPs), and response regulators (ARRs). Recent studies have suggested that the cytokinin TCS system is involved in a variety of other signaling and metabolic pathways. To further explore a potential function of the cytokinin TCS in the Arabidopsis dehydration stress response, we investigated the expression of all type-A ARR genes and a type-C ARR, ARR22, in both wild type and ahk single, double, and triple mutants in response to dehydration compared to cytokinin as well as dehydration tolerance of ahk mutants. We found that drought significantly induced the expression of a subset of ARR genes, ARR5, ARR7, ARR15, and ARR22. The results of expression analyses in ahk single, double, and triple mutants demonstrated that the cytokinin receptors AHK2 and AHK3 are redundantly involved in dehydration-inducible expression of ARR7, but not that of ARR5, ARR15, or ARR22. Dehydration tolerance assays showed that ahk2 and ahk3 single mutants exhibited enhanced dehydration tolerance compared with that of wild-type plants and ahk4 mutants, and that ahk2 ahk3 double mutants exhibited stronger drought tolerance than that of ahk3 ahk4, which exhibited more enhanced drought tolerance than that of wild-type plants and ahk single mutants. Taken together, these results demonstrate that while the cytokinin receptors AHK2 and AHK3 are critically involved in the dehydration tolerance response, both cytokinin receptor-dependent pathway and receptor-independent pathway occur in the dehydration response regulating ARR gene expression. In addition, preincubating ahk2, ahk3, ahk4, and the wild-type plants with cytokinin induced enhanced dehydration stress tolerance in these plants, demonstrating that cytokinins are involved in regulating plant response to dehydration stress.
拟南芥细胞分裂素信号转导利用由传感器组氨酸激酶（AHKs）、组氨酸磷酸转移蛋白（AHPs）和应答调节因子（ARRs）组成的多步骤双组分信号转导（TCS）系统。最近的研究表明，细胞分裂素 TCS 系统参与了多种其他信号转导和代谢途径。为了进一步探讨细胞分裂素 TCS 在拟南芥脱水胁迫反应中的潜在功能，我们研究了所有 A 型 ARR 基因和 C 型 ARR（ARR22）在野生型和 ahk 单突变体、双突变体和三突变体中的表达，与细胞分裂素和 ahk 突变体的脱水耐受性相比。我们发现干旱显著诱导了一部分 ARR 基因的表达，包括 ARR5、ARR7、ARR15 和 ARR22。在 ahk 单突变体、双突变体和三突变体中的表达分析结果表明，细胞分裂素受体 AHK2 和 AHK3 冗余地参与了 ARR7 的脱水诱导表达，但不参与 ARR5、ARR15 或 ARR22 的表达。脱水耐受性测定表明，ahk2 和 ahk3 单突变体与野生型植物和 ahk4 突变体相比表现出增强的脱水耐受性，ahk2 ahk3 双突变体比 ahk3 ahk4 更耐旱，而 ahk3 ahk4 比野生型植物和 ahk 单突变体更耐旱。总之，这些结果表明，虽然细胞分裂素受体 AHK2 和 AHK3 对于脱水耐受性反应至关重要，但在调节 ARR 基因表达方面，既存在细胞分裂素受体依赖途径，也存在受体非依赖途径。此外，用细胞分裂素预培养 ahk2、ahk3、ahk4 和野生型植物可诱导这些植物增强对脱水胁迫的耐受性，表明细胞分裂素参与调节植物对脱水胁迫的反应。
