Physiological and proteomic analyses reveal cAMP‐regulated key factors in maize root tolerance to heat stress

Abstract

Abstract 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.

Keywords

• ABA
• cAMP
• heat stress
• ion uptake
• maize root
• proteomics