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Rapid metabolic responses to pathogens are essential for plant survival and depend on numerous transcription factors. Mediator is the major transcriptional co-regulator for integration and transmission of signals from transcriptional regulators to RNA polymerase II. Using four Arabidopsis Mediator mutants, med16, med18, med25 and cdk8, we studied how differences in regulation of their transcript and metabolite levels correlate to their responses to Pseudomonas syringae infection. We found that med16 and cdk8 were susceptible, while med25 showed increased resistance. Glucosinolate, phytoalexin and carbohydrate levels were reduced already before infection in med16 and cdk8, but increased in med25, which also displayed increased benzenoids levels. Early after infection, wild type plants showed reduced glucosinolate and nucleoside levels, but increases in amino acids, benzenoids, oxylipins and the phytoalexin camalexin. The Mediator mutants showed altered levels of these metabolites and in regulation of genes encoding key enzymes for their metabolism. At later stage, mutants displayed defective levels of specific amino acids, carbohydrates, lipids and jasmonates which correlated to their infection response phenotypes. Our results reveal that MED16, MED25 and CDK8 are required for a proper, coordinated transcriptional response of genes which encode enzymes involved in important metabolic pathways for Arabidopsis responses to Pseudomonas syringae infections.

Biotic and abiotic stresses severely affect agriculture by affecting crop productivity, soil fertility, and health. These stresses may have significant financial repercussions, necessitating a practical, cost-effective, and ecologically friendly approach to lessen their negative impacts on plants. Several agrochemicals, such as fertilizers, pesticides, and insecticides, are used to improve plant health and protection; however, these chemical supplements have serious implications for human health. Plants being sessile cannot move or escape to avoid stress. Therefore, they have evolved to develop highly beneficial interactions with endophytes. The targeted use of beneficial plant endophytes and their role in combating biotic and abiotic stresses are gaining attention. Therefore, it is important to experimentally validate these interactions and determine how they affect plant fitness. This review highlights research that sheds light on how endophytes help plants tolerate biotic and abiotic stresses through plant–symbiont and plant–microbiota interactions. There is a great need to focus research efforts on this vital area to achieve a system-level understanding of plant–microbe interactions that occur naturally.

Plants, due to their sessile nature, face several environmental adversities. Abiotic stresses such as heat, cold, drought, heavy metals, and salinity are serious threats to plant production and yield. To cope with these stresses, plants have developed sophisticated mechanisms to avoid or resist stress conditions. A proper response to abiotic stress depends primarily on how plants perceive the stress signal, which in turn leads to initiation of signaling cascades and induction of resistance genes. New biotechnological tools such as RNA-seq and CRISPR-cas9 are quite useful in identifying target genes on a global scale, manipulating these genes to achieve tolerance, and helping breeders to develop stress-tolerant cultivars. In this review, we will briefly discuss the adverse effects of key abiotic stresses such as cold, heat, drought, and salinity. We will also discuss how plants sense various stresses and the importance of biotechnological tools in the development of stress-tolerant cultivars.

Drought stress retards plant growth and yield. Melatonin and nitric oxide (NO) have demonstrated their potential role against abiotic stresses; however, the underlying molecular mechanism by which they interact and extend drought stress tolerance has not been fully elucidated. Herein, the current study was performed to establish the optimum beneficial concentration of MT and NO in combating drought stress and later understand its responses at biochemical, and molecular levels. Results showed exogenous MT, and sodium nitroprusside (SNP as NO donor) have counteracted drought-induced growth inhibition of soybean (Glycine max L.) by increasing plant biomass, photosynthesis efficiency and water content and reducing reactive oxygen species accumulation. MT and NO treatments showed reduced lipid peroxidation and improved defense responses via significantly higher antioxidant enzyme activities than control during drought. Surprisingly, endogenous abscisic acid (ABA) contents and gene expression of its synthesis and ABA-responsive proteins and their promoters were significantly decreased in drought by MT + NO. This was coupled with an increase in endogenous MT levels. In endo-NO regulations, S-nitrosoglutathione was increased, but L-NAME (NO inhibitor) and cPTIO (NO scavenger) decreased the S-nitrosothiol (SNO) contents, which was followed by the increased expression of NO-synthesis-related-genes by MT + NO. Interestingly, MT + NO-induced drought stress tolerance was coupled with increased expression of transcription factors such as GmWRKY27 and GmMYB174. Conclusively, the physiological, antioxidant, and molecular analysis showed that MT triggers downregulated NO accumulation, promoting tolerance against drought stress.

After the discovery of nitric oxide (NO) as an important signaling molecule in plants, its involvement has been reported in several key physiological processes. At the cellular level, slight alterations in the quantity of NO or its various adducts, also known as reactive nitrogen intermediates (RNIs), have phenomenal implications. In plants this highly reactive, diatomic gaseous molecule regulates a plethora of physiological processes ranging from development, to reproduction, and defense against biotic and abiotic stresses. In animals, NO is produced enzymatically via the nitric oxide synthase (NOS) enzyme. However, after decades of research, it is now clear that in plants there is not one but several routes for NO production. Interestingly the discovery of a NOS enzyme in plants has remained an attractive topic of research for plant scientists over the years; the enzyme still remains elusive. In this chapter we briefly discuss the different pathways responsible for NO production in plants with special emphasis on the enzymatic production. We also discuss the NOS enzyme and its presence in lower and higher plants.

Nitric oxide (NO) and H₂O₂, known as signaling molecules, particularly regulate various cellular processes under stress conditions. Abiotic stress, like other stresses, leads to the production of reactive oxygen and nitrogen species (ROS and RNS, respectively). The interaction or crosstalk between these two redox molecules is important for the regulation of cellular processes. Increasing evidence has suggested that NO transfers its bioactivity through posttranslational modifications, the major among them is S-nitrosation, the covalent attachment of an NO moiety to a cysteine thiol that can bring conformational changes in proteins and hence in their functions. S-nitrosation of the tripeptide glutathione (GSH) results in the formation of S-nitrosoglutathione (GSNO), which is a relatively stable reservoir of NO. The formation of GSNO, therefore, determines cellular redox status, crucial for normal metabolic activities, and is regulated by key enzyme GSNO reductase (GSNOR) in plants. Here, we overview the importance of H₂O₂ and NO as signaling molecules in plants and their roles in stress tolerance. We also discuss crosstalk between H₂O₂ and NO and its importance in abiotic stress tolerance, with examples of salt, cold, drought, metal, and heat tolerance. The accumulated data from the cited research has important implications for the improved productivity of many crop plants.

Plants are in continuous conflict with the environmental constraints and their sessile nature demands a fine-tuned, well-designed defense mechanism that can cope with a multitude of biotic and abiotic assaults. Therefore, plants have developed innate immunity, R-gene-mediated resistance, and systemic acquired resistance to ensure their survival. Transcription factors (TFs) are among the most important genetic components for the regulation of gene expression and several other biological processes. They bind to specific sequences in the DNA called transcription factor binding sites (TFBSs) that are present in the regulatory regions of genes. Depending on the environmental conditions, TFs can either enhance or suppress transcriptional processes. In the last couple of decades, nitric oxide (NO) emerged as a crucial molecule for signaling and regulating biological processes. Here, we have overviewed the plant defense system, the role of TFs in mediating the defense response, and that how NO can manipulate transcriptional changes including direct post-translational modifications of TFs. We also propose that NO might regulate gene expression by regulating the recruitment of RNA polymerase during transcription.

Drought stress is a serious problem around the globe and particularly in the Republic of Iraq. Rice is the third most consumed crop for the Iraqi people; however, its cultivation and production is very low due to several challenges including drought. The current study was performed to evaluate five Iraqi rice cultivars along with relevant (drought-tolerant and drought-susceptible) controls under drought stress, either by treatment with 10% PEG (polyethylene glycol) or through water withholding to induce natural drought stress. The phenotypes of all the cultivars were evaluated and the transcriptional responses of key drought-responsive candidate genes, identified through the EST-SSR marker-based approach, were studied. We also studied transcript accumulation of drought-related transcriptional factors, such as OsGRASS23, OsbZIP12, and OsDREB2A. Moreover, the reference cultivars also included a drought-tolerant inter-specific cultivar Nerica 7 (a cross between Oryza sativa ssp. indica X O. glaberrima). Among the cultivars, the more drought-tolerant phenotypic characteristics and higher transcript accumulation of drought-related marker genes OsE647 and OsE1899 and transcriptional factors OsGRASS23, OsbZIP12, and OsDREB2A were observed in four (out of five) significantly drought-tolerant Iraqi cultivars; Mashkab, followed by Furat, Yasmen, and Amber 33. On another note, Amber Barka was found to be significantly drought susceptible. Mashkab and Amber Barka were found to be the most drought-tolerant and-susceptible cultivars, respectively. The identified tolerant cultivars may potentially serve as a genetic source for the incorporation of drought-tolerant phenotypes in rice.