High temperature constitutes a serious threat to crops. 3′,5′-cyclic adenosine monophosphate (cAMP) is increasingly proved to play important roles in plants. However, the mechanism of cAMP-mediated thermotolerance in root remains unclear. This study was designed to investigate cAMP roles in thermotolerance of maize root. Adenylyl cyclase (AC) catalyzes ATP to generate cAMP. For two identified maize AC genes, ZmRPP13-LK3 and ZmPSiP, the predictive ABA response element was found in their promoter fragments. Both ABA and heat stress treatment increased the promoter activity of ZmRPP13-LK3 and ZmPSiP. In the roots of maize ABA-deficient mutant vp5, the heat-caused increase of these two gene expression and cAMP content was obviously less than that in the roots of its wild-type Vp5. cAMP pretreatment decreased H₂O₂ and malondialdehyde content, but increased the activities of superoxide dismutase and ascorbate peroxidase in roots compared to no pretreatment under heat stress. By iTRAQ proteomics analysis, 268 cAMP-mediated differentially expressed proteins (DEPs) were identified from maize roots exposed to heat stress. The integrated analysis of these DEPs showed that cAMP was involved in many important biological processes, including ion uptake, protein degradation via autophagy or ubiquitin–proteasome system, a rapid delivery of stress-related cargo molecules by vesicle trafficking, and adaptation response by defense proteins. To determine whether the gene expression of these DEPs was regulated by cAMP and ABA, the gene expression of randomly selected 15 DEPs as ion transporters and heat shock proteins was analyzed, and the results indicated that cAMP and ABA pretreatment also enhanced the expression of their genes. Additionally, the cAMP pretreatment increased Ca²⁺, PO₄³⁻, and NO₃⁻ uptake, but reduced K⁺ uptake in roots under heat stress. All above-mentioned results suggest that ABA-mediated cAMP signaling may contribute to better thermotolerance in maize roots.

中文翻译：

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生理学和蛋白质组学分析揭示了 cAMP 调控的玉米根对热胁迫耐受性的关键因素

高温对农作物构成严重威胁。3',5'-环磷酸腺苷 (cAMP) 越来越多地被证明在植物中发挥重要作用。然而，cAMP介导的根中耐热性的机制仍不清楚。本研究旨在研究 cAMP 在玉米根的耐热性中的作用。腺苷酸环化酶 (AC) 催化 ATP 生成 cAMP。对于两个已鉴定的玉米 AC 基因ZmRPP13 - LK3和ZmPSiP，在它们的启动子片段中发现了预测性 ABA 反应元件。ABA和热应激处理均增加了ZmRPP13 - LK3和ZmPSiP的启动子活性。在玉米 ABA 缺陷突变体vp的根中如图5所示，这两种基因表达和cAMP含量的热致增加明显低于其野生型Vp 5的根部。cAMP预处理降低了H ₂ O ₂和丙二醛含量，但与热胁迫下未预处理相比，增加了根中超氧化物歧化酶和抗坏血酸过氧化物酶的活性。通过 iTRAQ 蛋白质组学分析，从暴露于热应激的玉米根中鉴定出 268 个 cAMP 介导的差异表达蛋白 (DEP)。对这些 DEP 的综合分析表明，cAMP 参与了许多重要的生物过程，包括离子摄取、通过自噬或泛素-蛋白酶体系统进行的蛋白质降解、通过囊泡运输快速传递与压力相关的货物分子以及防御蛋白的适应反应. 为了确定这些 DEP 的基因表达是否受 cAMP 和 ABA 调节，分析了随机选择的 15 个作为离子转运蛋白和热休克蛋白的 DEP 的基因表达，结果表明，cAMP和ABA预处理也增强了它们基因的表达。此外，cAMP 预处理增加了 Ca²⁺、 PO ₄ ^3-和 NO ₃ ^-的吸收，但在热胁迫下根系对K ^{+的吸收减少。}所有上述结果表明 ABA 介导的 cAMP 信号可能有助于提高玉米根的耐热性。