Dual impact of elevated temperature on plant defence and bacterial virulence in Arabidopsis

Guard Cell Activity of PIF4 Represses Disease Resistance in Arabidopsis

Phytochrome Interacting Factor 4 (PIF4) plays a central role in coordinating plant growth regulation by integrating multiple environmental cues. However, studies on whether and how PIF4 regulates plant immunity have inconsistent findings. In this study, we investigated the role of PIF4 in disease resistance against Pst DC3000 by characterizing its loss-of-function mutants using different inoculation strategies. Our findings reveal that pif4 mutants exhibit enhanced disease resistance with spray inoculation but not with infiltration inoculation compared to wild-type plants, and that mutants displayed more closed stomata apertures, indicating that PIF4 promotes stomatal opening. Importantly, expression of PIF4 by a guard-cell-specific promoter was sufficient to restore disease resistance to the wild-type level in the pif4 mutant. Additionally, PIF4 overexpression enhances disease symptom development independent of disease resistance and chlorophyll degradation, while the loss of PIF4 function leads to higher chlorophyll accumulation. Thus, our findings highlight a crucial function of PIF4 in regulating stomata-mediated disease resistance and chlorophyll accumulation, providing new insights into the connection of growth and defense in plants.

Plant immune resilience to a changing climate: molecular insights and biotechnological roadmaps

Successful resistance to disease-causing pathogens is underpinned by properly regulated immune signalling and defence responses in plants. The plant immune system is controlled at multiple levels of gene and protein regulation-from chromatin-associated epigenetic processes to protein post-translational modifications. Optimal fine-tuning of plant immune signalling and responses is important to prevent plant disease development, which is being exacerbated by a globally changing climate. In this review, we focus on how changing climatic factors mechanistically intercept plant immunity at different levels of regulation (chromatin, transcriptional, post-transcriptional, translational, and post-translational). We specifically highlight recent studies that have provided molecular insights into critically important climate-sensitive nodes and mechanisms of the plant immune system. We then propose several potential future directions to build climate-resilient plant disease resistance using cutting-edge biotechnology. Overall, this conceptual understanding and promising biotechnological advances provide a foundational platform towards novel approaches to engineer plant immune resilience.

Phytochrome B promotes blast disease resistance and enhances yield in rice

Phytochromes are red/far-red light receptors that regulate various aspects of plant growth, development, and stress responses. The precise mechanism by which phytochrome B (PhyB)-mediated light signaling influences plant defense and development remains unclear. In this study, we showed that PhyB enhances rice (Oryza sativa) blast disease resistance, tillering, and grain size compared to wild-type plants. Notably, PhyB interacted with and degraded grassy tiller 1 (GT1), a negative regulator of tiller development. Knockdown of GT1 in a phyB background partially rescued the diminished tillering of phyB. However, GT1 negatively regulates rice resistance to blast, suggesting that PhyB degradation of GT1 promotes tillering but not blast resistance. Previously, PhyB was found to interact with and degrade phytochrome-interacting factor 15 (PIL15), a key regulator of seed development that reduces rice resistance to blast and seed size. pil15 mutation in phyB mutants rescued phyB seed size and blast resistance, suggesting that PhyB might interact with and degrade PIL15 to negatively regulate blast resistance and seed size. PIL15 directly activated sugar will be eventually exported transporter 2a (SWEET2a). sweet2a mutants were less susceptible to blast disease compared to wild type. Collectively, these data demonstrate that PhyB promotes rice yield and blast resistance by inhibiting the transcription factors GT1 and PIL15 and downstream signaling.

Distinct profiles of plant immune resilience revealed by natural variation in warm temperature-modulated disease resistance among Arabidopsis accessions

Elevated temperature suppresses the plant defence hormone salicylic acid (SA) by downregulating the expression of master immune regulatory genes CALMODULIN BINDING PROTEIN 60-LIKE G (CBP60g) and SYSTEMIC ACQUIRED RESISTANCE DEFICIENT1 (SARD1). However, previous studies in Arabidopsis thaliana plants have primarily focused on the accession Columbia-0 (Col-0), while the genetic determinants of intraspecific variation in Arabidopsis immunity under elevated temperature remain unknown. Here we show that BASIC HELIX LOOP HELIX 059 (bHLH059), a thermosensitive SA regulator at nonstress temperatures, does not regulate immune suppression under warmer temperatures. In agreement, temperature-resilient and -sensitive Arabidopsis accessions based on disease resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 did not correlate with bHLH059 polymorphisms. Instead, we found that temperature-resilient accessions exhibit varying CBP60g and SARD1 expression profiles, potentially revealing CBP60g/SARD1-dependent and independent mechanisms of immune resilience to warming temperature. We identified thermoresilient accessions that exhibited either temperature-sensitive or -insensitive induction of the SA biosynthetic gene ICS1 (direct target gene of CBP60g and SARD1) and SA hormone levels. Collectively, this study has unveiled the intraspecific diversity of Arabidopsis immune responses under warm temperatures, which could aid in predicting plant responses to climate change and provide foundational knowledge for climate-resilient crop engineering.

Expression analysis of defense signaling marker genes in Capsicum annuum in response to phytohormones elicitation

BACKGROUND

To tolerate biotic stress, plants employ phytohormones such as jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) to regulate the immune response against different pathogens. Phytohormone-responsive genes, known as "Defense signaling marker genes," are used to evaluate plant disease resistance during pathogen infection. Most information on these marker genes derives from studies on the model plant Arabidopsis thaliana. The present study was aimed analyze the effect of hormonal elicitation at different concentrations at 24 h pos-treatment in the transcript level of 8 traditional genes selected for molecular studies plant-pathogen interactions in Capsicum.

METHODS AND RESULTS

Chemical treatment was achieved by spraying leaves of in vitro seedlings C. annuum L. with 0.1 mM, 1 mM or 2.5 mM ET; 1 mM, 2.5 mM, or 5 mM SA; 2.5 mM BABA; or 0.150 mM MeJA. Twenty-four hours after treatments were applied molecular analyses were carried out using qPCR to investigate the expression. Results revealed that 1 mM of ET or 0.15 mM of MeJA activated the expression CaPR1 (18--11.64-fold change), CaLOX2 (13.80-fold), CaAP2/ERF06 (22- 5.3- fold change), and CaPDF1.2 (2.3-1.5- fold). While, 5 mM of SA present effect of negative regulation on the expression in most of these genes.

CONCLUSIONS

Our results show that the expression profile induced by phytohormones in CaPR1 are particular in C. annuum, because were significantly induced for ET/MeJA, and dow-regulation with SA Contrary to Arabidopsis. Although, on both plants it is observed the cross talk between JA/ET and SA mediated signal pathways for the regulation of this gene.

Baking bad: plants in a toasty world with necrotrophs

Rising global temperatures pose a threat to plant immunity, making them more susceptible to diseases. The impact of temperature on plant immunity against biotrophic and hemi-biotrophic pathogens is well documented, while its effect on necrotrophs remains poorly understood. We venture into the uncharted territory of necrotrophic fungal pathogens in the face of rising temperatures. We discuss the role of the plant hormones salicylic acid (SA) and jasmonic acid (JA) in providing resistance to necrotrophs and delve into the temperature sensitivity of the SA pathway. Additionally, we explore the repercussions of increased temperatures on plant susceptibility to necrotrophs. We put forward a research agenda with an experimental framework aimed at providing a comprehensive understanding of how plants and pathogens adapt to increasing temperatures.

Reshaping the Primary Cell Wall: Dual Effects on Plant Resistance to Ralstonia solanacearum and Heat Stress Response

Temperature elevation drastically affects plant defense responses to Ralstonia solanacearum and inhibits the major source of resistance in Arabidopsis thaliana, which is mediated by the receptor pair RRS1-R/RPS4. In this study, we refined a previous genome-wide association (GWA) mapping analysis by using a local score approach and detected the primary cell wall CESA3 gene as a major gene involved in plant response to R. solanacearum at both 27°C and an elevated temperature, 30°C. We functionally validated CESA3 as a susceptibility gene involved in resistance to R. solanacearum at both 27 and 30°C through a reverse genetic approach. We provide evidence that the cesa3mre1 mutant enhances resistance to bacterial disease and that resistance is associated with an alteration of root cell morphology conserved at elevated temperatures. However, even by forcing the entry of the bacterium to bypass the primary cell wall barrier, the cesa3mre1 mutant still showed enhanced resistance to R. solanacearum with delayed onset of bacterial wilt symptoms. We demonstrated that the cesa3mre1 mutant had constitutive expression of the defense-related gene VSP1, which is upregulated at elevated temperatures, and that during infection, its expression level is maintained higher than in the wild-type Col-0. In conclusion, this study reveals that alteration of the primary cell wall by mutating the cellulose synthase subunit CESA3 contributes to enhanced resistance to R. solanacearum, remaining effective under heat stress. We expect that these results will help to identify robust genetic sources of resistance to R. solanacearum in the context of global warming. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

How Tea Plant Defends Against Blister Blight Disease: Facts Revealed and Unexplored Horizons

Tea (Camellia sinensis [L.] O. Kuntze) is cultivated as a beverage crop. Despite being a hardy perennial, the tea plant is susceptible to various biotic stresses. Among them, the foliar disease blister blight (BB) is considered the most serious threat to the tea industry, particularly in Asia. BB caused by Exobasidium vexans (Basidiomycetes) was first reported from Northern India in 1868 and gradually established in other tea-growing countries. The fungus E. vexans attacks young harvestable shoots and causes 20 to 50% crop loss. Over the past 150 years, scientific research has delved into various aspects of BB disease, including pathogen biology, disease cycle, epidemiology, disease forecasting, crop loss assessment, and disease management strategies. In a recent shift in research focus, scientists have begun to investigate the resistance mechanisms of tea plants against BB and apply this knowledge to commercial tea cultivation. Although progress has been significant in understanding the fundamental aspects of BB resistance, the detailed molecular mechanisms driving this resistance remain under investigation. This paper focuses on the current understanding of defense mechanisms employed by tea plants against E. vexans and, conversely, how E. vexans overcomes these defenses. Furthermore, we discuss the application of plant resistance strategies in commercial tea cultivation. Lastly, we identify existing research gaps and propose future research directions in the field.

The plant disease triangle facing climate change: a molecular perspective

Variations in climate conditions can dramatically affect plant health and the generation of climate-resilient crops is imperative to food security. In addition to directly affecting plants, it is predicted that more severe climate conditions will also result in greater biotic stresses. Recent studies have identified climate-sensitive molecular pathways that can result in plants being more susceptible to infection under unfavorable conditions. Here, we review how expected changes in climate will impact plant-pathogen interactions, with a focus on mechanisms regulating plant immunity and microbial virulence strategies. We highlight the complex interactions between abiotic and biotic stresses with the goal of identifying components and/or pathways that are promising targets for genetic engineering to enhance adaptation and strengthen resilience in dynamically changing environments.

INDUCER OF CBF EXPRESSION 1 promotes cold-enhanced immunity by directly activating salicylic acid signaling

Cold stress affects plant immune responses, and this process may involve the salicylic acid (SA) signaling pathway. However, the underlying mechanism by which low-temperature signals coordinate with SA signaling to regulate plant immunity remains unclear. Here, we found that low temperatures enhanced the disease resistance of Arabidopsis thaliana against Pseudomonas syringae pv. tomato DC3000. This process required INDUCER OF CBF EXPRESSION 1 (ICE1), the core transcription factor in cold-signal cascades. ICE1 physically interacted with NONEXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1), the master regulator of the SA signaling pathway. Enrichment of ICE1 on the PATHOGENESIS-RELATED GENE 1 (PR1) promoter and its ability to transcriptionally activate PR1 were enhanced by NPR1. Further analyses revealed that cold stress signals cooperate with SA signals to facilitate plant immunity against pathogen attack in an ICE1-dependent manner. Cold treatment promoted interactions of NPR1 and TGACG-BINDING FACTOR 3 (TGA3) with ICE1 and increased the ability of the ICE1-TGA3 complex to transcriptionally activate PR1. Together, our results characterize a critical role of ICE1 as an indispensable regulatory node linking low-temperature-activated and SA-regulated immunity. Understanding this crucial role of ICE1 in coordinating multiple signals associated with immunity broadens our understanding of plant-pathogen interactions.

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

Phylogenomic analyses and comparative genomics of Pseudomonas syringae associated with almond (Prunus dulcis) in California

We sequenced and comprehensively analysed the genomic architecture of 98 fluorescent pseudomonads isolated from different symptomatic and asymptomatic tissues of almond and a few other Prunus spp. Phylogenomic analyses, genome mining, field pathogenicity tests, and in vitro ice nucleation and antibiotic sensitivity tests were integrated to improve knowledge of the biology and management of bacterial blast and bacterial canker of almond. We identified Pseudomonas syringae pv. syringae, P. cerasi, and P. viridiflava as almond canker pathogens. P. syringae pv. syringae caused both canker and foliar (blast) symptoms. In contrast, P. cerasi and P. viridiflava only caused cankers, and P. viridiflava appeared to be a weak pathogen of almond. Isolates belonging to P. syringae pv. syringae were the most frequently isolated among the pathogenic species/pathovars, composing 75% of all pathogenic isolates. P. cerasi and P. viridiflava isolates composed 8.3 and 16.7% of the pathogenic isolates, respectively. Laboratory leaf infiltration bioassays produced results distinct from experiments in the field with both P. cerasi and P. syringae pv. syringae, causing significant necrosis and browning of detached leaves, whereas P. viridiflava conferred moderate effects. Genome mining revealed the absence of key epiphytic fitness-related genes in P. cerasi and P. viridiflava genomic sequences, which could explain the contrasting field and laboratory bioassay results. P. syringae pv. syringae and P. cerasi isolates harboured the ice nucleation protein, which correlated with the ice nucleation phenotype. Results of sensitivity tests to copper and kasugamycin showed a strong linkage to putative resistance genes. Isolates harbouring the ctpV gene showed resistance to copper up to 600 μg/ml. In contrast, isolates without the ctpV gene could not grow on nutrient agar amended with 200 μg/ml copper, suggesting ctpV can be used to phenotype copper resistance. All isolates were sensitive to kasugamycin at the label-recommended rate of 100μg/ml.

Fitness difference between two synonymous mutations of Phytophthora infestans ATP6 gene

BACKGROUND

Sequence variation produced by mutation provides the ultimate source of natural selection for species adaptation. Unlike nonsynonymous mutation, synonymous mutations are generally considered to be selectively neutral but accumulating evidence suggests they also contribute to species adaptation by regulating the flow of genetic information and the development of functional traits. In this study, we analysed sequence characteristics of ATP6, a housekeeping gene from 139 Phytophthora infestans isolates, and compared the fitness components including metabolic rate, temperature sensitivity, aggressiveness, and fungicide tolerance among synonymous mutations.

RESULTS

We found that the housekeeping gene exhibited low genetic variation and was represented by two major synonymous mutants at similar frequency (0.496 and 0.468, respectively). The two synonymous mutants were generated by a single nucleotide substitution but differed significantly in fitness as well as temperature-mediated spatial distribution and expression. The synonymous mutant ending in AT was more common in cold regions and was more expressed at lower experimental temperature than the synonymous mutant ending in GC and vice versa.

CONCLUSION

Our results are consistent with the argument that synonymous mutations can modulate the adaptive evolution of species including pathogens and have important implications for sustainable disease management, especially under climate change.

Protist ubiquitin ligase effector PbE3-2 targets cysteine protease RD21A to impede plant immunity

Clubroot, caused by the soil-borne protist pathogen Plasmodiophora brassicae, is one of the most devastating diseases of Brassica oil and vegetable crops worldwide. Understanding the pathogen infection strategy is crucial for the development of disease control. However, because of its obligate biotrophic nature, the molecular mechanism by which this pathogen promotes infection remains largely unknown. P. brassicae E3 ubiquitin ligase 2 (PbE3-2) is a Really Interesting New Gene (RING)-type E3 ubiquitin ligase in P. brassicae with E3 ligase activity in vitro. Yeast (Saccharomyces cerevisiae) invertase assay and apoplast washing fluid extraction showed that PbE3-2 harbors a functional signal peptide. Overexpression of PbE3-2 in Arabidopsis (Arabidopsis thaliana) resulted in higher susceptibility to P. brassicae and decreases in chitin-triggered reactive oxygen species burst and expression of marker genes in salicylic acid signaling. PbE3-2 interacted with and ubiquitinated host cysteine protease RESPONSIVE TO DEHYDRATION 21A (RD21A) in vitro and in vivo. Mutant plants deficient in RD21A exhibited similar susceptibility and compromised immune responses as in PbE3-2 overexpression plants. We show that PbE3-2, which targets RD21A, is an important virulence factor for P. brassicae. Two other secretory RING-type E3 ubiquitin ligases in P. brassicae performed the same function as PbE3-2 and ubiquitinated RD21A. This study reveals a substantial virulence functional role of protist E3 ubiquitin ligases and demonstrates a mechanism by which protist E3 ubiquitin ligases degrade host immune-associated cysteine proteases to impede host immunity.

Local Application of Acibenzolar-S-Methyl Treatment Induces Antiviral Responses in Distal Leaves of Arabidopsis thaliana

Systemic acquired resistance (SAR) is a plant defense mechanism that provides protection against a broad spectrum of pathogens in distal tissues. Recent studies have revealed a concerted function of salicylic acid (SA) and N-hydroxypipecolic acid (NHP) in the establishment of SAR against bacterial pathogens, but it remains unknown whether NHP is also involved in SAR against viruses. We found that the local application of acibenzolar-S-methyl (ASM), a synthetic analog of SA, suppressed plantago asiatica mosaic virus (PlAMV) infection in the distal leaves of Arabidopsis thaliana. This suppression of infection in untreated distal leaves was observed at 1 day, but not at 3 days, after application. ASM application significantly increased the expression of SAR-related genes, including PR1, SID2, and ALD1 after 1 day of application. Viral suppression in distal leaves after local ASM application was not observed in the sid2-2 mutant, which is defective in isochorismate synthase 1 (ICS1), which is involved in salicylic acid synthesis; or in the fmo1 mutant, which is defective in the synthesis of NHP; or in the SA receptor npr1-1 mutant. Finally, we found that the local application of NHP suppressed PlAMV infection in the distal leaves. These results indicate that the local application of ASM induces antiviral SAR against PlAMV through a mechanism involving NHP.

Plants and global warming: challenges and strategies for a warming world

KEY MESSAGE

In this review, we made an attempt to create a holistic picture of plant response to a rising temperature environment and its impact by covering all aspects from temperature perception to thermotolerance. This comprehensive account describing the molecular mechanisms orchestrating these responses and potential mitigation strategies will be helpful for understanding the impact of global warming on plant life. Organisms need to constantly recalibrate development and physiology in response to changes in their environment. Climate change-associated global warming is amplifying the intensity and periodicity of these changes. Being sessile, plants are particularly vulnerable to variations happening around them. These changes can cause structural, metabolomic, and physiological perturbations, leading to alterations in the growth program and in extreme cases, plant death. In general, plants have a remarkable ability to respond to these challenges, supported by an elaborate mechanism to sense and respond to external changes. Once perceived, plants integrate these signals into the growth program so that their development and physiology can be modulated befittingly. This multifaceted signaling network, which helps plants to establish acclimation and survival responses enabled their extensive geographical distribution. Temperature is one of the key environmental variables that affect all aspects of plant life. Over the years, our knowledge of how plants perceive temperature and how they respond to heat stress has improved significantly. However, a comprehensive mechanistic understanding of the process still largely elusive. This review explores how an increase in the global surface temperature detrimentally affects plant survival and productivity and discusses current understanding of plant responses to high temperature (HT) and underlying mechanisms. We also highlighted potential resilience attributes that can be utilized to mitigate the impact of global warming.

Small holes, big impact: Stomata in plant-pathogen-climate epic trifecta

The regulation of stomatal aperture opening and closure represents an evolutionary battle between plants and pathogens, characterized by adaptive strategies that influence both plant resistance and pathogen virulence. The ongoing climate change introduces further complexity, affecting pathogen invasion and host immunity. This review delves into recent advances on our understanding of the mechanisms governing immunity-related stomatal movement and patterning with an emphasis on the regulation of stomatal opening and closure dynamics by pathogen patterns and host phytocytokines. In addition, the review explores how climate changes impact plant-pathogen interactions by modulating stomatal behavior. In light of the pressing challenges associated with food security and the unpredictable nature of climate changes, future research in this field, which includes the investigation of spatiotemporal regulation and engineering of stomatal immunity, emerges as a promising avenue for enhancing crop resilience and contributing to climate control strategies.

Dual RNA-Seq Reveals Temperature-Mediated Gene Reprogramming and Molecular Crosstalk between Grapevine and Lasiodiplodia theobromae

High temperatures associated with a fluctuating climate profoundly accelerate the occurrence of a myriad of plant diseases around the world. A comprehensive insight into how plants respond to pathogenic microorganisms under high-temperature stress is required for plant disease management, whereas the underlying mechanisms behind temperature-mediated plant immunity and pathogen pathogenicity are still unclear. Here, we evaluated the effect of high temperature on the development of grapevine canker disease and quantified the contribution of temperature variation to the gene transcription reprogramming of grapevine and its pathogenic agent Lasiodiplodia theobromae using a dual RNA-seq approach. The results showed that both grapevine and the pathogen displayed altered transcriptomes under different temperatures, and even the transcription of a plethora of genes from the two organisms responded in different directions and magnitudes. The transcription variability that arose due to temperature oscillation allowed us to identify a total of 26 grapevine gene modules and 17 fungal gene modules that were correlated with more than one gene module of the partner organism, which revealed an extensive web of plant-pathogen gene reprogramming during infection. More importantly, we identified a set of temperature-responsive genes that were transcriptionally orchestrated within the given gene modules. These genes are predicted to be involved in multiple cellular processes including protein folding, stress response regulation, and carbohydrate and peptide metabolisms in grapevine and porphyrin- and pteridine-containing compound metabolisms in L. theobromae, implying that in response to temperature oscillation, a complex web of signaling pathways in two organism cells is activated during infection. This study describes a co-transcription network of grapevine and L. theobromae in the context of considering temperature variation, which provides novel insights into deciphering the molecular mechanisms underlying temperature-modulated disease development.

Effects of Elevated Temperature on Pisum sativum Nodule Development: I-Detailed Characteristic of Unusual Apical Senescence

Despite global warming, the influence of heat on symbiotic nodules is scarcely studied. In this study, the effects of heat stress on the functioning of nodules formed by Rhizobium leguminosarum bv. viciae strain 3841 on pea (Pisum sativum) line SGE were analyzed. The influence of elevated temperature was analyzed at histological, ultrastructural, and transcriptional levels. As a result, an unusual apical pattern of nodule senescence was revealed. After five days of exposure, a senescence zone with degraded symbiotic structures was formed in place of the distal nitrogen fixation zone. There was downregulation of various genes, including those associated with the assimilation of fixed nitrogen and leghemoglobin. After nine days, the complete destruction of the nodules was demonstrated. It was shown that nodule recovery was possible after exposure to elevated temperature for 3 days but not after 5 days (which coincides with heat wave duration). At the same time, the exposure of plants to optimal temperature during the night leveled the negative effects. Thus, the study of the effects of elevated temperature on symbiotic nodules using a well-studied pea genotype and Rhizobium strain led to the discovery of a novel positional response of the nodule to heat stress.

From the classroom to the farm: a lesson plan that promotes smallholder farmers' education and training about plant pathology in the context of climate change

Climate change represents one of the biggest threats to agricultural productivity around the world. In the tropics, extreme climate and pest and disease outbreaks represent one of the biggest climate change threats to smallholder farmers. Understanding smallholder farmers' educational needs and increasing access to information and awareness of climate change through education and training are key first steps to enhance the adaptive capacity of smallholder farmers. In a primary effort to increase accessible training and education to these communities, we developed a plant pathology lesson plan. The lesson plan introduces basic concepts in plant pathology and disease management using diverse educational activities focused on experiential and collaborative learning. This lesson plan may have implications in enhancing farmers' adaptive capacity and increasing accessible education to underrepresented farming communities around the world.

High air humidity dampens salicylic acid pathway and NPR1 function to promote plant disease

The occurrence of plant disease is determined by interactions among host, pathogen, and environment. Air humidity shapes various aspects of plant physiology and high humidity has long been known to promote numerous phyllosphere diseases. However, the molecular basis of how high humidity interferes with plant immunity to favor disease has remained elusive. Here we show that high humidity is associated with an "immuno-compromised" status in Arabidopsis plants. Furthermore, accumulation and signaling of salicylic acid (SA), an important defense hormone, are significantly inhibited under high humidity. NPR1, an SA receptor and central transcriptional co-activator of SA-responsive genes, is less ubiquitinated and displays a lower promoter binding affinity under high humidity. The cellular ubiquitination machinery, particularly the Cullin 3-based E3 ubiquitin ligase mediating NPR1 protein ubiquitination, is downregulated under high humidity. Importantly, under low humidity the Cullin 3a/b mutant plants phenocopy the low SA gene expression and disease susceptibility that is normally observed under high humidity. Our study uncovers a mechanism by which high humidity dampens a major plant defense pathway and provides new insights into the long-observed air humidity influence on diseases.

Acclimation response and management strategies to combat heat stress in wheat for sustainable agriculture: A state-of-the-art review

Unpredicted variability in climate change on the planet is associated with frequent extreme high-temperature events impacting crop yield globally. Wheat is an economically and nutritionally important crop that fulfils global food requirements and each degree rise in temperature results in ∼6% of its yield reduction. Thus, understanding the impact of climate change, especially the terminal heat stress on global wheat production, becomes critically important for policymakers, crop breeders, researchers and scientists to ensure global food security. This review describes how wheat perceives heat stress and induces stress adaptation events by its morpho-physiological, phenological, molecular, and biochemical makeup. Temperature above a threshold level in crop vicinity leads to irreversible injuries, viz. destruction of cellular membranes and enzymes, generation of active oxygen species, redox imbalance, etc. To cope with these changes, wheat activates its heat tolerance mechanisms characterized by hoarding up soluble carbohydrates, signalling molecules, and heat tolerance gene expressions. Being vulnerable to heat stress, increasing wheat production without delay seeks strategies to mitigate the detrimental effects and provoke the methods for its sustainable development. Thus, to ensure the crop's resilience to stress and increasing food demand, this article circumscribes the integrated management approaches to enhance wheat's performance and adaptive capacity besides its alleviating risks of increasing temperature anticipated with climate change. Implementing these integrated strategies in the face of risks from rising temperatures will assist us in producing sustainable wheat with improved yield.

Extra- and intranuclear heat perception and triggering mechanisms in plants

The escalating impact of global warming on crop yield and quality poses a significant threat to future food supplies. Breeding heat-resistant crop varieties holds promise, but necessitates a deeper understanding of the molecular mechanisms underlying plant heat tolerance. Recent studies have shed light on the initial events of heat perception in plants. In this review, we provide a comprehensive summary of the recent progress made in unraveling the mechanisms of heat perception and response in plants. Calcium ion (Ca2+), hydrogen peroxide (H2O2), and nitric oxide (NO) have emerged as key participants in heat perception. Furthermore, we discuss the potential roles of the NAC transcription factor NTL3, thermo-tolerance 3.1 (TT3.1), and Target of temperature 3 (TOT3) as thermosensors associated with the plasma membrane. Additionally, we explore the involvement of cytoplasmic HISTONE DEACETYLASE 9 (HDA9), mRNA encoding the phytochrome-interacting factor 7 (PIF7), and chloroplasts in mediating heat perception. This review also highlights the role of intranuclear transcriptional condensates formed by phytochrome B (phyB), EARLY FLOWERING 3 (ELF3), and guanylate-binding protein (GBP)-like GTPase 3 (GBPL3) in heat perception. Finally, we raise the unresolved questions in the field of heat perception that require further investigation in the future.

Crosstalk and trade-offs: Plant responses to climate change-associated abiotic and biotic stresses

As sessile organisms, plants are constantly challenged by a dynamic growing environment. This includes fluctuations in temperature, water availability, light levels, and changes in atmospheric constituents such as carbon dioxide (CO2 ) and ozone (O3 ). In concert with changes in abiotic conditions, plants experience changes in biotic stress pressures, including plant pathogens and herbivores. Human-induced increases in atmospheric CO2 levels have led to alterations in plant growth environments that impact their productivity and nutritional quality. Additionally, it is predicted that climate change will alter the prevalence and virulence of plant pathogens, further challenging plant growth. A knowledge gap exists in the complex interplay between plant responses to biotic and abiotic stress conditions. Closing this gap is crucial for developing climate resilient crops in the future. Here, we briefly review the physiological responses of plants to elevated CO2 , temperature, tropospheric O3 , and drought conditions, as well as the interaction of these abiotic stress factors with plant pathogen pressure. Additionally, we describe the crosstalk and trade-offs involved in plant responses to both abiotic and biotic stress, and outline targets for future work to develop a more sustainable future food supply considering future climate change.

A critical role of a eubiotic microbiota in gating proper immunocompetence in Arabidopsis

Although many studies have shown that microbes can ectopically stimulate or suppress plant immune responses, the fundamental question of whether the entire preexisting microbiota is indeed required for proper development of plant immune response remains unanswered. Using a recently developed peat-based gnotobiotic plant growth system, we found that Arabidopsis grown in the absence of a natural microbiota lacked age-dependent maturation of plant immune response and were defective in several aspects of pattern-triggered immunity. Axenic plants exhibited hypersusceptibility to infection by the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and the fungal pathogen Botrytis cinerea. Microbiota-mediated immunocompetence was suppressed by rich nutrient conditions, indicating a tripartite interaction between the host, microbiota and abiotic environment. A synthetic microbiota composed of 48 culturable bacterial strains from the leaf endosphere of healthy Arabidopsis plants was able to substantially restore immunocompetence similar to plants inoculated with a soil-derived community. In contrast, a 52-member dysbiotic synthetic leaf microbiota overstimulated the immune transcriptome. Together, these results provide evidence for a causal role of a eubiotic microbiota in gating proper immunocompetence and age-dependent immunity in plants.

CURLY LEAF modulates apoplast liquid water status in Arabidopsis leaves

The apoplast of plant leaves, the intercellular space between mesophyll cells, is normally largely filled with air with a minimal amount of liquid water in it, which is essential for key physiological processes such as gas exchange to occur. Phytopathogens exploit virulence factors to induce a water-rich environment, or "water-soaked" area, in the apoplast of the infected leaf tissue to promote disease. We propose that plants evolved a "water soaking" pathway, which normally keeps a nonflooded leaf apoplast for plant growth but is disturbed by microbial pathogens to facilitate infection. Investigation of the "water soaking" pathway and leaf water control mechanisms is a fundamental, yet previously overlooked, aspect of plant physiology. To identify key components in the "water soaking" pathway, we performed a genetic screen to isolate Arabidopsis (Arabidopsis thaliana) severe water soaking (sws) mutants that show liquid water overaccumulation in the leaf under high air humidity, a condition required for visible water soaking. Here, we report the sws1 mutant, which displays rapid water soaking upon high humidity treatment due to a loss-of-function mutation in CURLY LEAF (CLF), encoding a histone methyltransferase in the POLYCOMB REPRESSIVE COMPLEX 2 (PRC2). We found that the sws1 (clf) mutant exhibits enhanced abscisic acid (ABA) levels and stomatal closure, which are indispensable for its water soaking phenotype and mediated by CLF's epigenetic regulation of a group of ABA-associated NAM, ATAF, and CUC (NAC) transcription factor genes, NAC019/055/072. The clf mutant showed weakened immunity, which likely also contributes to the water soaking phenotype. In addition, the clf plant supports a substantially higher level of Pseudomonas syringae pathogen-induced water soaking and bacterial multiplication, in an ABA pathway and NAC019/055/072-dependent manner. Collectively, our study sheds light on an important question in plant biology and demonstrates CLF as a key modulator of leaf liquid water status via epigenetic regulation of the ABA pathway and stomatal movement.

Mutagenesis of the melon Prv gene by CRISPR/Cas9 breaks papaya ringspot virus resistance and generates an autoimmune allele with constitutive defense responses

The majority of plant disease resistance (R) genes encode nucleotide binding-leucine-rich repeat (NLR) proteins. In melon, two closely linked NLR genes, Fom-1 and Prv, were mapped and identified as candidate genes that control resistance to Fusarium oxysporum f.sp. melonis races 0 and 2, and to papaya ringspot virus (PRSV), respectively. In this study, we validated the function of Prv and showed that it is essential for providing resistance against PRSV infection. We generated CRISPR/Cas9 [clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9] mutants using Agrobacterium-mediated transformation of a PRSV-resistant melon genotype, and the T1 progeny proved susceptible to PRSV, showing strong disease symptoms and viral spread upon infection. Three alleles having 144, 154, and ~3 kb deletions, respectively, were obtained, all of which caused loss of resistance. Interestingly, one of the Prv mutant alleles, prvΔ154, encoding a truncated product, caused an extreme dwarf phenotype, accompanied by leaf lesions, high salicylic acid levels, and defense gene expression. The autoimmune phenotype observed at 25 °C proved to be temperature dependent, being suppressed at 32 °C. This is a first report on the successful application of CRISPR/Cas9 to confirm R gene function in melon. Such validation opens up new opportunities for molecular breeding of disease resistance in this important vegetable crop.

XCP1 cleaves Pathogenesis-related protein 1 into CAPE9 for systemic immunity in Arabidopsis

Proteolytic activation of cytokines regulates immunity in diverse organisms. In animals, cysteine-dependent aspartate-specific proteases (caspases) play central roles in cytokine maturation. Although the proteolytic production of peptide cytokines is also essential for plant immunity, evidence for cysteine-dependent aspartate-specific proteases in regulating plant immunity is still limited. In this study, we found that the C-terminal proteolytic processing of a caspase-like substrate motif "CNYD" within Pathogenesis-related protein 1 (PR1) generates an immunomodulatory cytokine (CAPE9) in Arabidopsis. Salicylic acid enhances CNYD-targeted protease activity and the proteolytic release of CAPE9 from PR1 in Arabidopsis. This process involves a protease exhibiting caspase-like enzyme activity, identified as Xylem cysteine peptidase 1 (XCP1). XCP1 exhibits a calcium-modulated pH-activity profile and a comparable activity to human caspases. XCP1 is required to induce systemic immunity triggered by pathogen-associated molecular patterns. This work reveals XCP1 as a key protease for plant immunity, which produces the cytokine CAPE9 from the canonical salicylic acid signaling marker PR1 to activate systemic immunity.

Lipo-chitooligosaccharide and thuricin 17 act as plant growth promoters and alleviate drought stress in Arabidopsis thaliana

Lipo-chito-oligosaccharide (LCO-from Bradyrhizobium japonicum) and thuricin 17 (Th17-from Bacillus thuringiensis) are bacterial signal compounds from the rhizosphere of soybean that have been shown to enhance plant growth in a range of legumes and non-legumes. In this study, an attempt to quantify phytohormones involved in the initial hours after exposure of Arabidopsis thaliana to these compounds was conducted using UPLC-ESI-MS/MS. A petri-plate assay was conducted to screen for drought stress tolerance to PEG 8000 infusion and plant growth was studied 21-days post-stress. Arabidopsis thaliana plants grown in trays with drought stress imposed by water withhold were used for free proline determination, elemental analysis, and untargeted proteomics using LC-MS/MS studies. At 24 h post-exposure to the signal compounds under optimal growth conditions, Arabidopsis thaliana rosettes varied in their responses to the two signals. While LCO-treated rosettes showed a decrease in total IAA, cytokinins, gibberellins, and jasmonic acid, increases in ABA and SA was very clear. Th17-treated rosettes, on the other hand, showed an increase in IAA and SA. Both treatments resulted in decreased JA levels. Under severe drought stress imposed by PEG 8000 infusion, LCO and Th17 treatments were found to significantly increase fresh and dry weight over drought-stressed control plates, indicating that the presence of the signaling compounds decreased the negative effects experienced by the plants. Free proline content increased in LCO- and Th17-treated plants after water-withhold drought stress. Elemental analysis showed a significant increase in carbon percentage at the lower concentration of Th17. Untargeted proteomics revealed changes in the levels of drought-specific ribosomal proteins, glutathione S-transferase, late embryogenesis proteins, vegetative storage proteins 1 and 2, thaumatin-like proteins, and those related to chloroplast and carbon metabolism. The roles of some of these significantly affected proteins detected under drought stress are discussed.

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.

Light and temperature perceptions go through a phase separation

Light and temperature are two distinct but closely linked environmental factors that profoundly affect plant growth and development. Biomolecular condensates are membraneless micron-scale compartments formed through liquid-liquid phase separation, which have been shown to be involved in a wide range of biological processes. In the last few years, biomolecular condensates are emerged to serve as phase separation-based sensors for plant sensing and/or responding to external environmental cues. This review summarizes the recently reported plant biomolecular condensates in sensing light and temperature signals. The current understanding of the biophysical properties and the action modes of phase separation-based environmental sensors are highlighted. Unresolved questions and possible challenges for future studies of phase-separation sensors are also discussed.

The OsSGS3-tasiRNA-OsARF3 module orchestrates abiotic-biotic stress response trade-off in rice

Recurrent heat stress and pathogen invasion seriously threaten crop production, and abiotic stress often antagonizes biotic stress response against pathogens. However, the molecular mechanisms of trade-offs between thermotolerance and defense remain obscure. Here, we identify a rice thermo-sensitive mutant that displays a defect in floret development under high temperature with a mutation in SUPPRESSOR OF GENE SILENCING 3a (OsSGS3a). OsSGS3a interacts with its homolog OsSGS3b and modulates the biogenesis of trans-acting small interfering RNA (tasiRNA) targeting AUXIN RESPONSE FACTORS (ARFs). We find that OsSGS3a/b positively, while OsARF3a/b and OsARF3la/lb negatively modulate thermotolerance. Moreover, OsSGS3a negatively, while OsARF3a/b and OsARF3la/lb positively regulate disease resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) and the fungal pathogen Magnaporthe oryzae (M. oryzae). Taken together, our study uncovers a previously unknown trade-off mechanism that regulates distinct immunity and thermotolerance through the OsSGS3-tasiRNA-OsARF3 module, highlighting the regulation of abiotic-biotic stress response trade-off in plants.

Structural diversity and stress regulation of the plant immunity-associated CALMODULIN-BINDING PROTEIN 60 (CBP60) family of transcription factors in Solanum lycopersicum (tomato)

Cellular signaling generates calcium (Ca2+) ions, which are ubiquitous secondary messengers decoded by calcium-dependent protein kinases, calcineurins, calreticulin, calmodulins (CAMs), and CAM-binding proteins. Previous studies in the model plant Arabidopsis thaliana have shown the critical roles of the CAM-BINDING PROTEIN 60 (CBP60) protein family in plant growth, stress responses, and immunity. Certain CBP60 factors can regulate plant immune responses, like pattern-triggered immunity, effector-triggered immunity, and synthesis of major plant immune-activating metabolites salicylic acid (SA) and N-hydroxypipecolic acid (NHP). Although homologous CBP60 sequences have been identified in the plant kingdom, their function and regulation in most species remain unclear. In this paper, we specifically characterized 11 members of the CBP60 family in the agriculturally important crop tomato (Solanum lycopersicum). Protein sequence analyses revealed that three CBP60 homologs have the closest amino acid identity to Arabidopsis CBP60g and SARD1, master transcription factors involved in plant immunity. Strikingly, AlphaFold deep learning-assisted prediction of protein structures highlighted close structural similarity between these tomato and Arabidopsis CBP60 homologs. Conserved domain analyses revealed that they possess CAM-binding domains and DNA-binding domains, reflecting their potential involvement in linking Ca2+ signaling and transcriptional regulation in tomato plants. In terms of their gene expression profiles under biotic (Pseudomonas syringae pv. tomato DC3000 pathogen infection) and/or abiotic stress (warming temperatures), five tomato CBP60 genes were pathogen-responsive and temperature-sensitive, reminiscent of Arabidopsis CBP60g and SARD1. Overall, we present a genome-wide identification of the CBP60 gene/protein family in tomato plants, and we provide evidence on their regulation and potential function as Ca2+-sensing transcriptional regulators.

A Jasmonic Acid-Related Mechanism Affects ARGONAUTE5 Expression and Antiviral Defense Against Potato Virus X in Arabidopsis thaliana

During virus infection, Argonaute (AGO) proteins bind to Dicer-produced virus small interfering RNAs and target viral RNA based on sequence complementarity, thereby limiting virus proliferation. The Arabidopsis AGO2 protein is important for resistance to multiple viruses, including potato virus X (PVX). In addition, AGO5 is important in systemic defense against PVX. Normally AGO5 is expressed only in reproductive tissues, and its induction by virus infection is thought to be important for its participation in antiviral defense. However, it is unclear what mechanisms induce AGO5 expression in response to virus infection. Here, we show that dde2-2, a mutant compromised in jasmonic acid (JA) biosynthesis, displays constitutive upregulation of AGO5. This mutant also showed increased resistance to PVX and this resistance was dependent on a functional AGO5 gene. Furthermore, methyl jasmonate treatment ablated AGO5 expression in leaves during virus infection and resulted in increased susceptibility to virus. Our results further support a role for AGO5 in antiviral RNA silencing and a negative regulation by JA, a plant hormone associated with defense against plant-feeding arthropods, which are often the vectors of plant viruses. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

CBP60-DB: An AlphaFold-predicted plant kingdom-wide database of the CALMODULIN-BINDING PROTEIN 60 protein family with a novel structural clustering algorithm

Molecular genetic analyses in the model species Arabidopsis thaliana have demonstrated the major roles of different CALMODULIN-BINDING PROTEIN 60 (CBP60) proteins in growth, stress signaling, and immune responses. Prominently, CBP60g and SARD1 are paralogous CBP60 transcription factors that regulate numerous components of the immune system, such as cell surface and intracellular immune receptors, MAP kinases, WRKY transcription factors, and biosynthetic enzymes for immunity-activating metabolites salicylic acid (SA) and N-hydroxypipecolic acid (NHP). However, their function, regulation, and diversification in most species remain unclear. Here, we have created CBP60-DB (https://cbp60db.wlu.ca/), a structural and bioinformatic database that comprehensively characterized 1052 CBP60 gene homologs (encoding 2376 unique transcripts and 1996 unique proteins) across 62 phylogenetically diverse genomes in the plant kingdom. We have employed deep learning-predicted structural analyses using AlphaFold2 and then generated dedicated web pages for all plant CBP60 proteins. Importantly, we have generated a novel clustering visualization algorithm to interrogate kingdom-wide structural similarities for more efficient inference of conserved functions across various plant taxa. Because well-characterized CBP60 proteins in Arabidopsis are known to be transcription factors with putative calmodulin-binding domains, we have integrated external bioinformatic resources to analyze protein domains and motifs. Collectively, we present a plant kingdom-wide identification of this important protein family in a user-friendly AlphaFold-anchored database, representing a novel and significant resource for the broader plant biology community.

The Phantom Menace: latest findings on effector biology in the rice blast fungus

Magnaporthe oryzae is a hemibiotrophic fungus responsible for the economically devastating and recalcitrant rice blast disease. However, the blast fungus is not only restricted to rice plants as it can also infect wheat, millet, and other crops. Despite previous outstanding discoveries aimed to understand and control the disease, the fungus remains one of the most important pathogens that threatens global food security. To cause disease, M. oryzae initiates morphological changes to attach, penetrate, and colonize rice cells, all while suppressing plant immune defenses that would otherwise hinder its proliferation. As such, M. oryzae actively secretes a battery of small proteins called "effectors" to manipulate host machinery. In this review, we summarize the latest findings in effector identification, expression, regulation, and functionality. We review the most studied effectors and their roles in pathogenesis. Additionally, we discern the current methodologies to structurally catalog effectors, and we highlight the importance of climate change and its impact on the future of rice blast disease.

Temperature changes in the root ecosystem affect plant functionality

Climate change is increasing the frequency of extreme heat events that aggravate its negative impact on plant development and agricultural yield. Most experiments designed to study plant adaption to heat stress apply homogeneous high temperatures to both shoot and root. However, this treatment does not mimic the conditions in natural fields, where roots grow in a dark environment with a descending temperature gradient. Excessively high temperatures severely decrease cell division in the root meristem, compromising root growth, while increasing the division of quiescent center cells, likely in an attempt to maintain the stem cell niche under such harsh conditions. Here, we engineered the TGRooZ, a device that generates a temperature gradient for in vitro or greenhouse growth assays. The root systems of plants exposed to high shoot temperatures but cultivated in the TGRooZ grow efficiently and maintain their functionality to sustain proper shoot growth and development. Furthermore, gene expression and rhizosphere or root microbiome composition are significantly less affected in TGRooZ-grown roots than in high-temperature-grown roots, correlating with higher root functionality. Our data indicate that use of the TGRooZ in heat-stress studies can improve our knowledge of plant response to high temperatures, demonstrating its applicability from laboratory studies to the field.

Red-light receptor phytochrome B inhibits BZR1-NAC028-CAD8B signaling to negatively regulate rice resistance to sheath blight

Phytochrome (Phy)-regulated light signalling plays important roles in plant growth, development, and stress responses. However, its function in rice defence against sheath blight disease (ShB) remains unclear. Here, we found that PhyB mutation or shade treatment promoted rice resistance to ShB, while resistance was reduced by PhyB overexpression. Further analysis showed that PhyB interacts with phytochrome-interacting factor-like 15 (PIL15), brassinazole resistant 1 (BZR1), and vascular plant one-zinc-finger 2 (VOZ2). Plants overexpressing PIL15 were more susceptible to ShB in contrast to bzr1-D-overexpressing plants compared with the wild-type, suggesting that PhyB may inhibit BZR1 to negatively regulate rice resistance to ShB. Although BZR1 is known to regulate brassinosteroid (BR) signalling, the observation that BR signalling negatively regulated resistance to ShB indicated an independent role for BZR1 in controlling rice resistance. It was also found that the BZR1 ligand NAC028 positively regulated resistance to ShB. RNA sequencing showed that cinnamyl alcohol dehydrogenase 8B (CAD8B), involved in lignin biosynthesis was upregulated in both bzr1-D- and NAC028-overexpressing plants compared with the wild-type. Yeast-one hybrid, ChIP, and transactivation assays demonstrated that BZR1 and NAC028 activate CAD8B directly. Taken together, the analyses demonstrated that PhyB-mediated light signalling inhibits the BZR1-NAC028-CAD8B pathway to regulate rice resistance to ShB.

Mechanistic models to meet the challenge of climate change in plant-pathogen systems

Evidence that climate change will impact the ecology and evolution of individual plant species is growing. However, little, as yet, is known about how climate change will affect interactions between plants and their pathogens. Climate drivers could affect the physiology, and thus demography, and ultimately evolutionary processes affecting both plant hosts and their pathogens. Because the impacts of climate drivers may operate in different directions at different scales of infection, and, furthermore, may be nonlinear, abstracting across these processes may mis-specify outcomes. Here, we use mechanistic models of plant-pathogen interactions to illustrate how counterintuitive outcomes are possible, and we introduce how such framing may contribute to understanding climate effects on plant-pathogen systems. We discuss the evidence-base derived from wild and agricultural plant-pathogen systems that could inform such models, specifically in the direction of estimates of physiological, demographic and evolutionary responses to climate change. We conclude by providing an overview of knowledge gaps and directions for future research in this important area. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Xanthomonas infection and ozone stress distinctly influence the microbial community structure and interactions in the pepper phyllosphere

While the physiological and transcriptional response of the host to biotic and abiotic stresses have been intensely studied, little is known about the resilience of associated microbiomes and their contribution towards tolerance or response to these stresses. We evaluated the impact of elevated tropospheric ozone (O3), individually and in combination with Xanthomonas perforans infection, under open-top chamber field conditions on overall disease outcome on resistant and susceptible pepper cultivars, and their associated microbiome structure, function, and interaction network across the growing season. Pathogen infection resulted in a distinct microbial community structure and functions on the susceptible cultivar, while concurrent O3 stress did not further alter the community structure, and function. However, O3 stress exacerbated the disease severity on resistant cultivar. This altered diseased severity was accompanied by enhanced heterogeneity in associated Xanthomonas population counts, although no significant shift in overall microbiota density, microbial community structure, and function was evident. Microbial co-occurrence networks under simultaneous O3 stress and pathogen challenge indicated a shift in the most influential taxa and a less connected network, which may reflect the altered stability of interactions among community members. Increased disease severity on resistant cultivar may be explained by such altered microbial co-occurrence network, indicating the altered microbiome-associated prophylactic shield against pathogens under elevated O3. Our findings demonstrate that microbial communities respond distinctly to individual and simultaneous stressors, in this case, O3 stress and pathogen infection, and can play a significant role in predicting how plant-pathogen interactions would change in the face of climate change.

Assessment of Black Rot in Oilseed Rape Grown under Climate Change Conditions Using Biochemical Methods and Computer Vision

Global warming is a challenge for plants and pathogens, involving profound changes in the physiology of both contenders to adapt to the new environmental conditions and to succeed in their interaction. Studies have been conducted on the behavior of oilseed rape plants and two races (1 and 4) of the bacterium Xanthomonas campestris pv. campestris (Xcc) and their interaction to anticipate our response in the possible future climate. Symptoms caused by both races of Xcc were very similar to each other under any climatic condition assayed, although the bacterial count from infected leaves differed for each race. Climate change caused an earlier onset of Xcc symptoms by at least 3 days, linked to oxidative stress and a change in pigment composition. Xcc infection aggravated the leaf senescence already induced by climate change. To identify Xcc-infected plants early under any climatic condition, four classifying algorithms were trained with parameters obtained from the images of green fluorescence, two vegetation indices and thermography recorded on Xcc-symptomless leaves. Classification accuracies were above 0.85 out of 1.0 in all cases, with k-nearest neighbor analysis and support vector machines performing best under the tested climatic conditions.

Effect of temperature and humidity on dynamics and transmission of Pseudomonas amygdali pv. lachrymans aerosols

Cucumber angular leaf spot (ALS) disease, caused by Pseudomonas amygdali pv. lachrymans (Pal), is an emerging disease with a high incidence that causes severe damage to cucumber worldwide. Bacterial aerosols play a crucial role in the epidemiology of greenhouse ALS disease. However, little is known about the influence of temperature and relative humidity (RH) on the dynamics of Pal in aerosols. A study was conducted to investigate the relationships between the concentration of Pal aerosols and their dependence on temperature and RH in aerosol chambers and greenhouses. The results demonstrated that temperature and RH are both significant factors influencing the release amount, survival time and infectivity of Pal in aerosols, while RH has a greater influence on particle size than temperature across the range of conditions tested. The release amount and survival time of Pal in aerosols under high RH (95%) and low temperature (≤ 25°C) conditions were significantly higher than those under low RH (35%) and high temperature (35°C) conditions. The highest release amount of Pal aerosol (96 CFU/m³) and highest survival rate (98.41%) were found at 18°C and 95% RH, while the highest disease index (DI = 60.9) caused by Pal aerosol was found at 25°C and 95% RH. In addition, Pal aerosols presented a larger diameter (4.7->7.0 μm) under high RH (95% RH) than under dry conditions (≤ 65% RH). These findings will play a crucial role in elucidating the influence of environmental parameters on the dynamics and transmission of Pal in aerosols. Based on our findings, preliminary recommendations for controlling airborne Pal spread involve controlling air temperature and RH, which will contribute to the effective alleviation and control of cucumber ALS disease.

Optical Sensing Technologies to Elucidate the Interplay between Plant and Microbes

Plant-microbe interactions are critical for ecosystem functioning and driving rhizosphere processes. To fully understand the communication pathways between plants and rhizosphere microbes, it is crucial to measure the numerous processes that occur in the plant and the rhizosphere. The present review first provides an overview of how plants interact with their surrounding microbial communities, and in turn, are affected by them. Next, different optical biosensing technologies that elucidate the plant-microbe interactions and provide pathogenic detection are summarized. Currently, most of the biosensors used for detecting plant parameters or microbial communities in soil are centered around genetically encoded optical and electrochemical biosensors that are often not suitable for field applications. Such sensors require substantial effort and cost to develop and have their limitations. With a particular focus on the detection of root exudates and phytohormones under biotic and abiotic stress conditions, novel low-cost and in-situ biosensors must become available to plant scientists.

Climate change challenges, plant science solutions

Climate change is a defining challenge of the 21st century, and this decade is a critical time for action to mitigate the worst effects on human populations and ecosystems. Plant science can play an important role in developing crops with enhanced resilience to harsh conditions (e.g. heat, drought, salt stress, flooding, disease outbreaks) and engineering efficient carbon-capturing and carbon-sequestering plants. Here, we present examples of research being conducted in these areas and discuss challenges and open questions as a call to action for the plant science community.

Plant N-acylethanolamines play a crucial role in defense and its variation in response to elevated CO2 and temperature in tomato

The ubiquitous lipid-derived molecules N-acylethanolamines (NAEs) have multiple immune functions in mammals, but their roles and mechanisms in plant defense response during changing environment remain largely unclear. Here, we found that exogenous NAE18:0 and NAE18:2 promoted defense against the necrotrophic pathogen Botrytis cinerea but suppressed defense to the hemi-biotrophic pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 in tomato. The knocking-down and overexpression function analysis of the pathogen-responsive NAE synthetic gene PHOSPHOLIPASE Dγ (PLDγ) and hydrolytic gene FATTY ACID AMID HYDROLASE 1 (FAAH1) revealed that the NAE pathway is crucial for plant defense response. Using exogenous applications and SA-abolished NahG plants, we unveiled the antagonistic relationship between NAE and SA in plant defense response. Elevated CO₂ and temperature significantly changed the NAE pathway in response to pathogens, while inhibition of the NAE pathway led to the alternation of environment-mediated defense variations against Pst DC3000 in tomato, indicating that NAE pathway is associated with plant defense variations in response to elevated CO₂ and temperature. The results herein reveal a new function of NAE in plant defense, and its involvement in environment-mediated defense variation in tomato. These findings shed light on the NAE-based plant defense, which may have relevance to crop disease management in future changing climate.

Too hot to defend: a tale of salicylic acid

Extreme temperatures threaten plant immunity by suppressing the salicylic acid (SA) biosynthesis via unknown mechanisms. Kim et al. demonstrated that suppression of the SA pathway and plant immunity can be rescued by optimised expression of two master immune regulator(s), advancing our prospects for better protecting plants in a warming climate.

Plant Signals Anticipate the Induction of the Type III Secretion System in Pseudomonas syringae pv. actinidiae, Facilitating Efficient Temperature-Dependent Effector Translocation

Disease resistance in plants depends on a molecular dialogue with microbes that involves many known chemical effectors, but the time course of the interaction and the influence of the environment are largely unknown. The outcome of host-pathogen interactions is thought to reflect the offensive and defensive capabilities of both players. When plants interact with Pseudomonas syringae, several well-characterized virulence factors contribute to early bacterial pathogenicity, including the type III secretion system (T3SS), which must be activated by signals from the plant and environment to allow the secretion of virulence effectors. The manner in which these signals regulate T3SS activity is still unclear. Here, we strengthen the paradigm of the plant-pathogen molecular dialogue by addressing overlooked details concerning the timing of interactions, specifically the role of plant signals and temperature on the regulation of bacterial virulence during the first few hours of the interaction. Whole-genome expression profiling after 1 h revealed that the perception of plant signals from kiwifruit or tomato extracts anticipated T3SS expression in P. syringae pv. actinidiae compared to apoplast-like conditions, facilitating more efficient effector transport in planta, as revealed by the induction of a temperature-dependent hypersensitive response in the nonhost plant Arabidopsis thaliana Columbia-0 (Col-0). Our results show that in the arms race between plants and bacteria, the temperature-dependent timing of bacterial virulence versus the induction of plant defenses is probably one of the fundamental parameters governing the outcome of the interaction. IMPORTANCE Plant diseases-their occurrence and severity-result from the impact of three factors: the host, the pathogen, and the environmental conditions, interconnected in the disease triangle. Time was further included as a fourth factor accounting for plant disease, leading to a more realistic three-dimensional disease pyramid to represent the evolution of disease over time. However, this representation still considers time only as a parameter determining when and to what extent a disease will occur, at a scale from days to months. Here, we show that time is a factor regulating the arms race between plants and pathogens, at a scale from minutes to hours, and strictly depends on environmental factors. Thus, besides the arms possessed by pathogens and plants per se, the opportunity and the timing of arms mobilization make the difference in determining the outcome of an interaction and thus the occurrence of plant disease.