Climate change impedes plant immunity mechanisms

CRISPR/Cas9-mediated mutagenesis of rice NAC transcription factor genes results in altered innate immunity

Mutating transcription factor genes involved in growth, development, and stress response in rice enhances disease resistance to microbial pathogens without suffering a yield penalty.

Ozone Treatment as an Approach to Induce Specialized Compounds in Melissa officinalis Plants

Plants are constantly subjected to environmental changes that deeply affect their metabolism, leading to the inhibition or synthesis of "specialized" compounds, small organic molecules that play a fundamental role in adaptative responses. In this work, Melissa officinalis L. (an aromatic plant broadly cultivated due to the large amounts of secondary metabolites) plants were exposed to realistic ozone (O3) dosages (80 ppb, 5 h day-1) for 35 consecutive days with the aim to evaluate its potential use as elicitor of specialized metabolite production. Ozone induced stomatal dysfunction throughout the whole experiment, associated with a low photosynthetic performance, a decrease in the potential energy conversion activity of PSII, and an alteration in the total chlorophyll content (-35, -36, -10, and -17% as average compared to the controls, respectively). The production of hydrogen peroxide at 7 days from the beginning of exposure (+47%) resulted in lipid peroxidation and visible injuries. This result suggests metabolic disturbance within the cell and a concomitant alteration in cell homeostasis, probably due to a limited activation of antioxidative mechanisms. Moderate accumulated doses of O3 triggered the accumulation of hydroxycinnamic acids and the up-regulation of the genes encoding enzymes involved in rosmarinic acid, phenylpropanoid, and flavonoid biosynthesis. While high accumulated doses of O3 significantly enhanced the content of hydroxybenzoic acid and flavanone glycosides. Our study shows that the application of O3 at the investigated concentration for a limited period (such as two/three weeks) may become a useful tool to stimulate bioactive compounds production in M. officinalis.

OsWRKY7 contributes to pattern-triggered immunity against Xanthomonas oryzae pv. oryzae

Rice is a staple crop continually threatened by bacterial and fungal pathogens. OsWRKY transcription factors are involved in various disease responses. However, the functions of many OsWRKYs are still elusive. In this study, we demonstrated that OsWRKY7 enhances rice immunity against Xanthomonas oryzae pv. oryzae (Xoo). OsWRKY7 localized in the nucleus, and gene expression of OsWRKY7 was induced by Xoo inoculation. The OsWRKY7-overexpressing lines showed enhanced resistant phenotype against Xoo, and gene expressions of OsPR1a, OsPR1b, and OsPR10a were significantly increased in the transgenic lines after Xoo inoculation. Moreover, OsWRKY7 activated the OsPR promoters, and the promoter activities were synergistically upregulated by flg22. Genetic- and cell-based analysis showed OsWRKY7 is involved in pattern-triggered immunity against Xoo. These results suggest that OsWRKY7 plays a role as a positive regulator of disease resistance to Xoo through pattern-triggered immunity.

Systemic analysis of metabolome reconfiguration in Arabidopsis after abiotic stressors uncovers metabolites that modulate defense against pathogens

Understanding plant immune responses is complex because of the high interdependence among biological processes in homeostatic networks. Hence, the integration of environmental cues causes network rewiring that interferes with defense responses. Similarly, plants retain molecular signatures configured under abiotic stress periods to rapidly respond to recurrent stress, and these can alter immunity. Metabolome changes imposed by abiotic stressors are persistent, although their impact on defense remains to be clarified. In this study, we profiled metabolomes of Arabidopsis plants under several abiotic stress treatments applied individually or simultaneously to capture temporal trajectories in metabolite composition during adverse conditions and recovery. Further systemic analysis was performed to address the relevance of metabolome changes and extract central features to be tested in planta. Our results demonstrate irreversibility in major fractions of metabolome changes as a general pattern in response to abiotic stress periods. Functional analysis of metabolomes and co-abundance networks points to convergence in the reconfiguration of organic acid and secondary metabolite metabolism. Arabidopsis mutant lines for components related to these metabolic pathways showed altered defense capacities against different pathogens. Collectively, our data suggest that sustained metabolome changes configured in adverse environments can act as modulators of immune responses and provide evidence for a new layer of regulation in plant defense.

The rice SnRK family: biological roles and cell signaling modules

Stimulus-activated signaling pathways orchestrate cellular responses to control plant growth and development and mitigate the effects of adverse environmental conditions. During this process, signaling components are modulated by central regulators of various signal transduction pathways. Protein phosphorylation by kinases is one of the most important events transmitting signals downstream, via the posttranslational modification of signaling components. The plant serine and threonine kinase SNF1-related protein kinase (SnRK) family, which is classified into three subgroups, is highly conserved in plants. SnRKs participate in a wide range of signaling pathways and control cellular processes including plant growth and development and responses to abiotic and biotic stress. Recent notable discoveries have increased our understanding of how SnRKs control these various processes in rice (Oryza sativa). In this review, we summarize current knowledge of the roles of OsSnRK signaling pathways in plant growth, development, and stress responses and discuss recent insights. This review lays the foundation for further studies on SnRK signal transduction and for developing strategies to enhance stress tolerance in plants.

Molecular regulation of the salicylic acid hormone pathway in plants under changing environmental conditions

Salicylic acid (SA) is a central plant hormone mediating immunity, growth, and development. Recently, studies have highlighted the sensitivity of the SA pathway to changing climatic factors and the plant microbiome. Here we summarize organizing principles and themes in the regulation of SA biosynthesis, signaling, and metabolism by changing abiotic/biotic environments, focusing on molecular nodes governing SA pathway vulnerability or resilience. We especially highlight advances in the thermosensitive mechanisms underpinning SA-mediated immunity, including differential regulation of key transcription factors (e.g., CAMTAs, CBP60g, SARD1, bHLH059), selective protein-protein interactions of the SA receptor NPR1, and dynamic phase separation of the recently identified GBPL3 biomolecular condensates. Together, these nodes form a biochemical paradigm for how the external environment impinges on the SA pathway.

Differential CaKAN3-CaHSF8 associations underlie distinct immune and heat responses under high temperature and high humidity conditions

High temperature and high humidity (HTHH) conditions increase plant susceptibility to a variety of diseases, including bacterial wilt in solanaceous plants. Some solanaceous plant cultivars have evolved mechanisms to activate HTHH-specific immunity to cope with bacterial wilt disease. However, the underlying mechanisms remain poorly understood. Here we find that CaKAN3 and CaHSF8 upregulate and physically interact with each other in nuclei under HTHH conditions without inoculation or early after inoculation with R. solanacearum in pepper. Consequently, CaKAN3 and CaHSF8 synergistically confer immunity against R. solanacearum via activating a subset of NLRs which initiates immune signaling upon perception of unidentified pathogen effectors. Intriguingly, when HTHH conditions are prolonged without pathogen attack or the temperature goes higher, CaHSF8 no longer interacts with CaKAN3. Instead, it directly upregulates a subset of HSP genes thus activating thermotolerance. Our findings highlight mechanisms controlling context-specific activation of high-temperature-specific pepper immunity and thermotolerance mediated by differential CaKAN3-CaHSF8 associations.

TMT-Based Proteomic Analysis of Hannaella sinensis-Induced Apple Resistance-Related Proteins

Studies on the molecular mechanism of antagonistic yeasts to control apple postharvest diseases are not comprehensive enough. Our preliminary investigations screened the biocontrol effect of Hannaella sinensis, an antagonistic yeast, and discovered its control efficacy on apple blue mold decay. However, the molecular mechanism of H. sinensis-induced resistance in apple has not been studied. In this study, proteins from apple treated with H. sinensis and sterile saline were analyzed using TMT proteomics technology. It was found that H. sinensis treatment induced the expressions of apple resistance-related proteins. Among the proteins in H. sinensis-induced apple, proteins related to plant defense mechanisms, such as reactive oxygen species scavenging, improvement of plant resistance and synthesis of resistant substances, improvement of plant disease resistance, the degradation of the pathogen cell wall, cell signaling, antibacterial activity, transport of defense-related substances, and protein processing, were differentially regulated. The results of this study revealed the underlying molecular mechanisms of H. sinensis-induced apple resistance at the protein level; the results also provided a theoretical basis for the commercial application of H. sinensis.

OsWRKY114 Is a Player in Rice Immunity against Fusarium fujikuroi

Every year, invasive pathogens cause significant damage to crops. Thus, identifying genes conferring broad-spectrum resistance to invading pathogens is critical for plant breeding. We previously demonstrated that OsWRKY114 contributes to rice (Oryza sativa L.) immunity against the bacterial pathovar Xanthomonas oryzae pv. oryzae (Xoo). However, it is not known whether OsWRKY114 is involved in defense responses to other pathogens. In this study, we revealed that OsWRKY114 enhances innate immunity in rice against the fungal pathogen Fusarium fujikuroi, which is the causal agent of bakanae disease. Transcript levels of various gibberellin-related genes that are required for plant susceptibility to F. fujikuroi were reduced in rice plants overexpressing OsWRKY114. Analysis of disease symptoms revealed increased innate immunity against F. fujikuroi in OsWRKY114-overexpressing rice plants. Moreover, the expression levels of OsJAZ genes, which encode negative regulators of jasmonic acid signaling that confer immunity against F. fujikuroi, were reduced in OsWRKY114-overexpressing rice plants. These results indicate that OsWRKY114 confers broad-spectrum resistance not only to Xoo but also to F. fujikuroi. Our findings provide a basis for developing strategies to mitigate pathogen attack and improve crop resilience to biotic stress.

Plant translational reprogramming for stress resilience

Organisms regulate gene expression to produce essential proteins for numerous biological processes, from growth and development to stress responses. Transcription and translation are the major processes of gene expression. Plants evolved various transcription factors and transcriptome reprogramming mechanisms to dramatically modulate transcription in response to environmental cues. However, even the genome-wide modulation of a gene's transcripts will not have a meaningful effect if the transcripts are not properly biosynthesized into proteins. Therefore, protein translation must also be carefully controlled. Biotic and abiotic stresses threaten global crop production, and these stresses are seriously deteriorating due to climate change. Several studies have demonstrated improved plant resistance to various stresses through modulation of protein translation regulation, which requires a deep understanding of translational control in response to environmental stresses. Here, we highlight the translation mechanisms modulated by biotic, hypoxia, heat, and drought stresses, which are becoming more serious due to climate change. This review provides a strategy to improve stress tolerance in crops by modulating translational regulation.