Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Abstract

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Keywords: abiotic stresses; climate change; plant physiology; signaling pathway; stress tolerance; transcription factor.

Figure 1

(A) Phylogenetic analysis of plant mitogen-activated protein kinases (MAPKs) and MAPK-likes in 13 plant species following Bayesian inference. Different colors indicate different species. The monocot clade and the PP sequence with the atypical MEY activation loop within the TEY-B clade are marked by asterisks. (B) Phylogenetic analysis of MAPKKKs in grapevine, apple, tomato, and Arabidopsis using the neighbor-joining (NJ) tree using MEGA-X with 1,000 bootstraps. Adapted from He et al. (2020) and Janitza et al. (2012), open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY).

Figure 2

The receptors after receiving the signals activate the specific mitogen-activated protein kinase (MAPK) proteins that are inactive before. Subsequently, MAP4K activates other MAPKs (including MAP2K and MAP3K) by phosphorylating the ST (S/T is serine/threonine) and TXY (T is threonine, Y is tyrosine, and X is any amino acid) motif in MAPKs (Rodriguez et al., 2010; Taj et al., 2010). As a result, MAPKs activate the transcription factors (TFs), enzymes, and other downstream kinases that transmit extracellular environmental signals to the cells that play a role in growth, development, stress response, and other physiological and biochemical processes (Zhang et al., 2018).

Figure 3

The schematic diagram of different mitogen-activated protein kinase (MAPK) signaling molecules under different stress conditions in different crops. Solid arrows show verified pathways; dashed arrows indicate assumed pathways; question marks indicate unknown cascade components.