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.

The potato (Solanum tuberosum L.), one of the most important food crops worldwide, is sensitive to environmental stresses. Sensor–responder complexes comprising calcineurin B-like (CBL) proteins and CBL-interacting protein kinases (CIPKs) not only modulate plant growth and development but also mediate numerous stress responses. Here, using a Hidden Markov Model and BLAST searches, 27 CIPK genes were identified in potato and divided into five groups by phylogenetic analysis and into two clades (intron-poor and intron-rich) by gene structure analysis. Quantitative reverse-transcription PCR (qRT-PCR) assays revealed that StCIPK genes play important roles in plant growth, development and abiotic stress tolerance. Up-regulated expression of StCIPK10 was significantly induced by drought, PEG6000 and ABA. StCIPK10 enhances both the ability of potato to scavenge reactive oxygen species and the content of corresponding osmoregulation substances, thereby strengthening tolerance to drought and osmotic stress. StCIPK10 is located at the intersection between the abscisic acid and abiotic stress signaling pathways, which control both root growth and stomatal closure in potato. In addition, StCIPK10 interacts with StCBL1, StCBL4, StCBL6, StCBL7, StCBL8, StCBL11 and StCBL12, and is specifically recruited to the plasma membrane by StCBL11.

The nuclear factor Y (NF-Y) family is comprised of transcription factors that have been implicated in multiple plant biological processes. However, little is known about this family in potato. In the present study, a total of 41 StNF-Y genes were identified in the potato genome. In addition, the phylogenetic, gene structure, motif, and chromosomal location of this family were analyzed. The tissue expression profiles based on RNA-seq data showed that 27 StNF-Y genes had tissue-specific expression, while the remaining 14 had low expression in all tissues. Publicly available transcriptomics data from various abiotic stresses revealed several stress-responsive StNF-Y genes, which were further verified via quantitative real-time polymerase chain reaction experiments. Furthermore, the StNF-YC9 gene was highly induced by dehydration and drought treatments. StNF-YC9 protein was mainly localized in the nucleus and cytoplasmic membrane. Overexpressing StNF-YC9 potato lines (OxStNF-YC9) had significantly increased in root length and exhibited stronger stomatal closure in potato treated by polyethylene-glycol and abscisic acid. In addition, OxStNF-YC9 lines had higher photosynthetic rates and decreased water loss under short-term drought stress compared to wild-type plants. During long-term drought stress, OxStNF-YC9 lines had higher proline levels, lower malondialdehyde content, and increased activity of several antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase. This study increased our understanding of the StNF-Y gene and suggested that StNF-YC9 played an important role in drought tolerance by increased the photosynthesis rate, antioxidant enzyme activity, and proline accumulation coupled to lowered malondialdehyde accumulation in potato.

Calcium-dependent protein kinases (CDPK) are implicated in signaling transduction in eukaryotic organisms. It is largely unknown whether StCDPK28 plays a role in the response to water deficiency and osmotic stress in potato plants (Solanum tuberosum L.). Potato cv. Zihuabai was cultivated under natural, moderate, and severe water deficiency conditions; to induce osmotic stress, potato plants were treated with 10% or 20% PEG. StCDPK28-overexpression and StCDPK28-knockdown plants were constructed. StCDPKs were evaluated by qRT-PCR. The subcellular location of the StCDPK28 protein was observed with confocal scanning laser microscopy. Phenotypic changes were indicated by photosynthetic activity, the contents of H₂O₂, MDA and proline, and the activities of CAT, SOD and POD. Results showed water deficiency and osmotic stress altered StCDPK expression patterns. StCDPK28 exhibited a membrane, cytosolic and nuclear localization. Water deficiency and osmotic stress induced StCDPK28 upregulation. Photosynthetic activity was enhanced by StCDPK28 overexpression, while decreased by StCDPK2 knockdown under water deficiency and osmotic stress. StCDPK28 overexpression decreased H₂O₂ and MDA, and increased proline, while StCDPK28 knockdown showed reverse results, compared with the wild type, in response to water deficiency and osmotic stress. StCDPK28 overexpression increased the activities of CAT, SOD and POD, while StCDPK28-knockdown plants indicated the reverse trend under water deficiency and osmotic stress conditions. Regulation of StCDPK28 expression could be a promising approach to improve the tolerance ability of potato plants in response to drought or high salt media.