Necrotrophic Fungus Botrytis Cinerea Research Articles

Ectopic expression of the grape hexose transporter VvHT5 restores STP13‐deficiency in Arabidopsis and promotes fungal resistance to Botrytis cinerea

AbstractSugar transporters play a crucial role in plant responses to environmental factors. During plant–pathogen interactions, it is well established that sugar transporters and cell wall invertases are essential for regulating sugar availability at the plant–pathogen interface, impacting both plant resistance and pathogen proliferation. Despite these insights, their role in grapevine defence against pathogens remains underexplored. We examined the expression of sugar transporter and invertase genes in grape leaves infected with the necrotrophic fungus Botrytis cinerea. Our results highlighted significant coordinated upregulation of VvHT5, VvcwINV and defence genes, suggesting a role in enhancing sink strength in infected leaves and implementing host defences. Heterologous expression of GFP‐fused proteins confirmed VvHT5 as a plasma membrane‐localized hexose symporter and phylogenetic analysis indicated its close relation with STP13‐like proteins, which are known to be implicated in host resistance across several plant–pathogen interactions. VvHT5 was heterologously expressed in Arabidopsis thaliana, resulting in high constitutive expression of the VvHT5 protein and increased glucose uptake activity. Phenotypic analysis revealed that VvHT5 enhanced basal resistance to B. cinerea and rescued the wild‐type phenotype in STP13‐deficient plants, indicating that VvHT5 is the grapevine orthologue of AtSTP13. Our findings suggest that VvHT5 may facilitate the reabsorption of extracellular monosaccharides, released from VvcwINV activity or damaged tissues during infection. This activity allows host cells to compete with necrotrophic pathogens for extracellular hexoses, thereby restricting sugar availability to the fungus. It would also support host metabolic demands for defence or serve as a signalling mechanism to orchestrate intracellular processes.

Suprathreshold Water Spray Stimulus Enhances Plant Defenses against Biotic Stresses in Tomato.

Mechanical stimuli can affect plant growth, development, and defenses. The role of water spray stimulation, as a prevalent mechanical stimulus in the environment, in crop growth and defense cannot be overlooked. In this study, the effects of water spray on tomato plant growth and defense against the chewing herbivore Helicoverpa armigera and necrotrophic fungus Botrytis cinerea were investigated. Suprathreshold water spray stimulus (LS) was found to enhance tomato plant defenses against pests and pathogens while concurrently modifying plant architecture. The results of the phytohormone and chemical metabolite analysis revealed that LS improved the plant defense response via jasmonic acid (JA) signaling. LS significantly elevated the level of a pivotal defensive metabolite, chlorogenic acid, and reduced the emissions of volatile organic compounds (VOCs) from tomato plants, thereby defending against pest and pathogen attacks. The most obvious finding to emerge from this study is that LS enhances tomato plant defenses against biotic stresses, which will pave the way for further work on the application of mechanical stimuli for pest management.

Morphological, genetic and pathogenic variability among Botrytis cinerea species complex causing gray mold of strawberry

The necrotrophic fungus Botrytis cinerea is capable of infecting more than 1400 plant species, encompassing both dicotyledons and monocotyledons. Recognized as the world's second most destructive fungal pathogen, B. cinerea is responsible for significant pre- and postharvest diseases, especially gray mold on a variety of economically important crops, vegetables, and fruits. This study focused on characterizing the variability of ten B. cinerea isolates from strawberry fruits harvested across various regions in Egypt. The differentiation among these isolates was evaluated through morphological, genetic, pathogenic, and biochemical methods. The isolates exhibited variation in cultural development, colony color, shape, margin, and texture. The study highlighted morphological differences in conidiophores, variations in conidia size, and sclerotia production on three different media. The ten Botrytis isolates have differed in mycelial growth rate and pathogenicity on strawberry fruits and positively correlated with oxalic acid production. Isolate B3 of B. cinerea was the most aggressive, while isolate B5 demonstrated the lowest. Two isolates of Botrytis represented the first occurrence of Botrytis species in Egypt, B. californica and B. eucalypti, which were identified using ITS sequencing and combined with morphological characteristics. They were also responsible for causing gray mold on strawberry fruits. These results are expected to greatly contribute to the knowledge of morphological and genetic variability in B. cinerea isolates, as well as offer valuable insights for the development of disease management strategies.

Grapevine gray mold disease: infection, defense and management.

Grapevine (Vitis vinifera L.,) is among the world's leading fruit crops. The production of grapes is severely affected by many diseases including gray mold, caused by the necrotrophic fungus Botrytis cinerea. Although all Vitis species can be hosts for B. cinerea, V. vinifera are particularly susceptible. Accordingly, this disease poses a significant threat to the grape industry and causes substantial economic losses. Development of resistant V. vinifera cultivars has progressed from incidental selection by farmers, to targeted selection through the use of statistics and experimental design, to the employment of genetic and genomic data. Emerging technologies such as marker-assisted selection and genetic engineering have facilitated the development of cultivars that possess resistance to B. cinerea. A promising method involves using the CRISPR/Cas9 system to induce targeted mutagenesis and develop genetically modified non-transgenic crops. Hence, scientists are now engaged in the active pursuit of identifying genes associated with susceptibility and resistance. This review focuses on the known mechanisms of interaction between the B. cinerea pathogen and its grapevine host. It also explores innate immune systems that have evolved in V. vinifera, with the objective of facilitating the rapid development of resistant grapevine cultivars.

Challenges and Opportunities Arising from Host-Botrytis cinerea Interactions to Outline Novel and Sustainable Control Strategies: The Key Role of RNA Interference.

The necrotrophic plant pathogenic fungus Botrytis cinerea (Pers., 1794), the causative agent of gray mold disease, causes significant losses in agricultural production. Control of this fungal pathogen is quite difficult due to its wide host range and environmental persistence. Currently, the management of the disease is still mainly based on chemicals, which can have harmful effects not only on the environment and on human health but also because they favor the development of strains resistant to fungicides. The flexibility and plasticity of B. cinerea in challenging plant defense mechanisms and its ability to evolve strategies to escape chemicals require the development of new control strategies for successful disease management. In this review, some aspects of the host-pathogen interactions from which novel and sustainable control strategies could be developed (e.g., signaling pathways, molecules involved in plant immune mechanisms, hormones, post-transcriptional gene silencing) were analyzed. New biotechnological tools based on the use of RNA interference (RNAi) are emerging in the crop protection scenario as versatile, sustainable, effective, and environmentally friendly alternatives to the use of chemicals. RNAi-based fungicides are expected to be approved soon, although they will face several challenges before reaching the market.

Modelling metabolic fluxes of tomato stems reveals that nitrogen shapes central metabolism for defence against Botrytis cinerea.

Among plant pathogens, the necrotrophic fungus Botrytis cinerea is one of the most prevalent, leading to severe crop damage. Studies related to its colonization of different plant species have reported variable host metabolic responses to infection. In tomato, high N availability leads to decreased susceptibility. Metabolic flux analysis can be used as an integrated method to better understand which metabolic adaptations lead to effective host defence and resistance. Here, we investigated the metabolic response of tomato infected by B. cinerea in symptomless stem tissues proximal to the lesions for 7 d post-inoculation, using a reconstructed metabolic model constrained by a large and consistent metabolic dataset acquired under four different N supplies. An overall comparison of 48 flux solution vectors of Botrytis- and mock-inoculated plants showed that fluxes were higher in Botrytis-inoculated plants, and the difference increased with a reduction in available N, accompanying an unexpected increase in radial growth. Despite higher fluxes, such as those involved in cell wall synthesis and other pathways, fluxes related to glycolysis, the tricarboxylic acid cycle, and amino acid and protein synthesis were limited under very low N, which might explain the enhanced susceptibility. Limiting starch synthesis and enhancing fluxes towards redox and specialized metabolism also contributed to defence independent of N supply.

Contrasting cytosolic glutathione redox dynamics under abiotic and biotic stress in barley as revealed by the biosensor Grx1-roGFP2.

Barley is a staple crop of major global importance and relatively resilient to a wide range of stress factors in the field. Transgenic reporter lines to investigate physiological parameters during stress treatments remain scarce. We generated and characterized transgenic homozygous barley lines (cv. Golden Promise Fast) expressing the genetically encoded biosensor Grx1-roGFP2, which indicates the redox potential of the major antioxidant glutathione in the cytosol. Our results demonstrated functionality of the sensor in living barley plants. We determined the glutathione redox potential (EGSH) of the cytosol to be in the range of -308 mV to -320 mV. EGSH was robust against a combined NaCl (150 mM) and water deficit treatment (-0.8 MPa) but responded with oxidation to infiltration with the phytotoxic secretome of the necrotrophic fungus Botrytis cinerea. The generated reporter lines are a novel resource to study biotic and abiotic stress resilience in barley, pinpointing that even severe abiotic stress leading to a growth delay does not automatically induce cytosolic EGSH oxidation, while necrotrophic pathogens can undermine this robustness.

In Vitro Analysis of the Antagonistic Biological and Chemical Interactions between the Endophyte Sordaria tomento-alba and the Phytopathogen Botrytis cinerea.

Plant pathogenic infections causing substantial global food losses are a persistent challenge. This study investigates a potential biocontrol strategy against the necrotrophic fungus Botrytis cinerea using the endophytic fungus Sordaria tomento-alba isolated from Gliricidia sepium in Colombia. Today, synthetic fungicides dominate B. cinerea control, raising environmental and health concerns. S. tomento-alba exhibits notable in vitro effects, inhibiting B. cinerea growth by approximately 60% during co-culture and 50% in double disc co-culture. Additionally, it suppresses botryanes production and produces the compound heptacyclosordariolone, which has proven effective in inhibiting B. cinerea mycelial growth and spore germination in vitro. This biocontrol agent could be a potential eco-friendly alternative to replace synthetic fungicides. Our study provides insights into the chemical and biological mechanisms underpinning the antagonistic activity of S. tomento-alba, emphasizing the need for further research to understand its biosynthesis pathways and optimize its biocontrol potential. It also contributes molecular evidence of fungal interactions with implications for advanced forums in molecular studies in biology and chemistry, particularly in addressing plant pathogenic infections and promoting sustainable agriculture.

Arabidopsis thaliana phosphoinositide-specific phospholipase C 2 is required for Botrytis cinerea proliferation

Phospholipase C (PLC) plays a key role in lipid signaling during plant development and stress responses. PLC activation is one of the earliest responses during pathogen perception. Arabidopsis thaliana contains seven PLC encoding genes (AtPLC1 to AtPLC7) and two pseudogenes (AtPLC8 and AtPLC9), being AtPLC2 the most abundant isoform with constitutive expression in all plant organs. PLC has been linked to plant defense signaling, in particular to the production of reactive oxygen species (ROS). Previously, we demonstrated that AtPLC2 is involved in ROS production via the NADPH oxidase isoforms RBOHD activation during stomata plant immunity. Here we studied the role of AtPLC2 on plant resistance against the necrotrophic fungus Botrytis cinerea, a broad host-range and serious agricultural pathogen. We show that the AtPLC2-silenced (amiR PLC2) or null mutant (plc2–1) plants developed smaller B. cinerea lesions. Moreover, plc2–1 showed less ROS production and an intensified SA-dependent signaling upon infection, indicating that B. cinerea uses AtPLC2-triggered responses for a successful proliferation. Therefore, AtPLC2 is a susceptibility (S) gene that facilitates B. cinerea infection and proliferation.

The apocarotenoid β-ionone regulates the transcriptome of Arabidopsis thaliana and increases its resistance against Botrytis cinerea.

Carotenoids are isoprenoid pigments indispensable for photosynthesis. Moreover, they are the precursor of apocarotenoids, which include the phytohormones abscisic acid (ABA) and strigolactones (SLs) as well as retrograde signaling molecules and growth regulators, such as β-cyclocitral and zaxinone. Here, we show that the application of the volatile apocarotenoid β-ionone (β-I) to Arabidopsis plants at micromolar concentrations caused a global reprogramming of gene expression, affecting thousands of transcripts involved in stress tolerance, growth, hormone metabolism, pathogen defense, and photosynthesis. This transcriptional reprogramming changes, along with induced changes in the level of the phytohormones ABA, jasmonic acid, and salicylic acid, led to enhanced Arabidopsis resistance to the widespread necrotrophic fungus Botrytis cinerea (B.c.) that causes the gray mold disease in many crop species and spoilage of harvested fruits. Pre-treatment of tobacco and tomato plants with β-I followed by inoculation with B.c. confirmed the effect of β-I in increasing the resistance to this pathogen in crop plants. Moreover, we observed reduced susceptibility to B.c. in fruits of transgenic tomato plants overexpressing LYCOPENE β-CYCLASE, which contains elevated levels of endogenous β-I, providing a further evidence for its effect on B.c. infestation. Our work unraveled β-I as a further carotenoid-derived regulatory metabolite and indicates the possibility of establishing this natural volatile as an environmentally friendly bio-fungicide to control B.c.

Frass from yellow mealworm (Tenebrio molitor) as plant fertilizer and defense priming agent

World population growth requires the development of a sustainable agriculture that allows feeding all the inhabitants of the planet, while reducing the use of agrochemicals. Currently, the insect farming industry for food and feed production is developing exponentially throughout the world; also producing insect frass with a potential utilization within agriculture and greenhouse industry. In the case of the yellow mealworm (Tenebrio molitor), few studies have been developed so far on the use of frass as a fertilizer, and there are none on its ability to activate plant defenses. By applying 2% sterilized mealworm frass to tomato we found a significant increase in its growth, demonstrating that the microbiota might not play a key role in its fertilizing capacity. In addition, the application of frass to sunflowers under different situations of nutritional deficit allowed us to determine what specific nutrients this fertilizer may be providing to the plant, finding a possible deficiency in the supply of N, but with sufficient amounts of P, K, Ca, and S. With respect to the induction of defenses, mealworm insect frass did not induce local root defenses in a root callose deposition assay in Arabidopsis thaliana under our experimental conditions. However, it activated systemic defenses in Arabidopsis thaliana by inducing defense genes in the absence of pathogen, further enhanced by infection with the necrotrophic fungus Botrytis cinerea. Therefore, mealworm frass could be a good fertilizer resource and plant defense inducer to support development of sustainable agriculture.

The Bcvic1 and Bcvic2 vegetative incompatibility genes in Botrytis cinerea encode proteins with domain architectures involved in allorecognition in other filamentous fungi

Vegetative incompatibility is a fungal allorecognition system characterised by the inability of genetically distinct conspecific fungal strains to form a viable heterokaryon and is controlled by multiple polymorphic loci termed vic (vegetative incompatibility) or het (heterokaryon incompatibility). We have genetically identified and characterised the first vic locus in the economically important, plant-pathogenic, necrotrophic fungus Botrytis cinerea. A bulked segregant approach coupled with whole genome Illumina sequencing of near-isogenic lines of B. cinerea was used to map a vic locus to a 60-kb region of the genome. Within that locus, we identified two adjacent, highly polymorphic open reading frames, Bcvic1 and Bcvic2, which encode predicted proteins that contain domain architectures implicated in vegetative incompatibility in other filamentous fungi. Bcvic1 encodes a predicted protein containing a putative serine esterase domain, a NACHT family of NTPases domain, and several Ankyrin repeats. Bcvic2 encodes a putative syntaxin protein containing a SNARE domain; such proteins typically function in vesicular transport. Deletion of Bcvic1 and Bcvic2 individually had no effect on vegetative incompatibility. However, deletion of the region containing both Bcvic1 and Bcvic2 resulted in mutant lines that were severely restricted in growth and showed loss of vegetative incompatibility. Complementation of these mutants by ectopic expression restored the growth and vegetative incompatibility phenotype, indicating that Bcvic1 and Bcvic2 are controlling vegetative incompatibility at this vic locus.

Transcriptomic and physiological shade avoidance responses in potato (Solanum tuberosum) plants.

Plants detect competitors in shaded environments by perceiving a reduction in photosynthetically active radiation (PAR) and the reduction between the red and far-red light (R:FR) ratio and blue photons. These light signals are detected by phytochromes and cryptochromes, which trigger shade avoidance responses such as shoot and petiole elongation and lead to increased susceptibility to pathogen attack. We studied morphological, anatomical, and photosynthesis differences in potato plants (Solanum tuberosum var. Spunta) exposed to sunlight or simulated shade in a greenhouse. We found that simulated shade strongly induced stem and internode elongation with a higher production of free auxin in stems and a lower production of tubers. The mesophyll thickness of the upper leaves of plants grown in simulated shade was lower, but the epidermis was wider compared with the leaves of plants cultivated in sunlight. In addition, the photosynthesis rate was lower in the upper leaves exposed to nonsaturated irradiances and higher in the basal leaves at saturated irradiances compared with control plants. RNA-seq analysis showed that 146 and 155 genes were up- and downregulated by shade, respectively. By quantitative reverse transcription polymerase chain reaction, we confirmed that FLOWERING LOCUS T (FT), WRKY-like, and PAR1b were induced, while FLAVONOL 4-SULFOTRANSFERASE was repressed under shade. In shaded plants, leaves and tubers were more susceptible to the necrotrophic fungus Botrytis cinerea attack. Overall, our work demonstrates configurational changes between growth and defense decisions in potato plants cultivated in simulated shade.

Expression of EPL1 from Trichoderma atroviride in Arabidopsis Confers Resistance to Bacterial and Fungal Pathogens.

During plant interaction with beneficial microorganisms, fungi secrete a battery of elicitors that trigger plant defenses against pathogenic microorganisms. Among the elicitor molecules secreted by Trichoderma are cerato-platanin proteins, such as EPL1, from Trichoderma atroviride. In this study, Arabidopsis thaliana plants that express the TaEPL1 gene were challenged with phytopathogens to evaluate whether expression of EPL1 confers increased resistance to the bacterial pathogen Pseudomonas syringae and the necrotrophic fungus Botrytis cinerea. Infection assays showed that Arabidopsis EPL1-2, EPL1-3, EPL1-4 expressing lines were more resistant to both pathogens in comparison to WT plants. After Pseudomonas syringae infection, there were reduced disease symptoms (e.g., small chlorotic spots) and low bacterial titers in the three 35S::TaEPL1 expression lines. Similarly; 35S::TaEPL1 expression lines were more resistant to Botrytis cinerea infection, showing smaller lesion size in comparison to WT. Interestingly, an increase in ROS levels was detected in 35S::TaEPL1 expression lines when compared to WT. A higher expression of SA- and JA-response genes occurred in the 35S::TaEPL1 lines, which could explain the resistance of these EPL1 expression lines to both pathogens. We propose that EPL1 is an excellent elicitor, which can be used to generate crops with improved resistance to broad-spectrum diseases.

Ubiquitylation of PHYTOSULFOKINE RECEPTOR 1 modulates the defense response in tomato.

Phytosulfokine (PSK) is a danger-associated molecular pattern recognized by PHYTOSULFOKINE RECEPTOR 1 (PSKR1) and initiates intercellular signaling to coordinate different physiological processes, especially in the defense response to the necrotrophic fungus Botrytis cinerea. The activity of peptide receptors is largely influenced by different posttranslational modifications, which determine intercellular peptide signal outputs. To date, the posttranslational modification to PHYTOSULFOKINE RECEPTOR 1 (PSKR1) remains largely unknown. Here, we show that tomato (Solanum lycopersicum) PSKR1 is regulated by the ubiquitin/proteasome degradation pathway. Using multiple protein-protein interactions and ubiquitylation analyses, we identified that plant U-box E3 ligases PUB12 and PUB13 interacted with PSKR1, among which PUB13 caused PSKR1 ubiquitylation at Lys-748 and Lys-905 sites to control PSKR1 abundance. However, this posttranslational modification was attenuated upon addition of PSK. Moreover, the disease symptoms observed in PUB13 knock-down and overexpression lines demonstrated that PUB13 significantly suppressed the PSK-initiated defense response. This highlights an important regulatory function for the turnover of a peptide receptor by E3 ligase-mediated ubiquitylation in the plant defense response.

AtBBX29 integrates photomorphogenesis and defense responses in Arabidopsis

Light is an environmental signal that modulates plant defenses against attackers. Recent research has focused on the effects of light on defense hormone signaling; however, the connections between light signaling pathways and the biosynthesis of specialized metabolites involved in plant defense have been relatively unexplored. Here, we show that Arabidopsis BBX29, a protein that belongs to the B-Box transcription factor (TF) family, integrates photomorphogenic signaling with defense responses by promoting flavonoid, sinapate and glucosinolate accumulation in Arabidopsis leaves. AtBBX29 transcript levels were up regulated by light, through photoreceptor signaling pathways. Genetic evidence indicated that AtBBX29 up-regulates MYB12 gene expression, a TF known to induce genes related to flavonoid biosynthesis in a light-dependent manner, and MYB34 and MYB51, which encode TFs involved in the regulation of glucosinolate biosynthesis. Thus, bbx29 knockout mutants displayed low expression levels of key genes of the flavonoid biosynthetic pathway, and the opposite was true in BBX29 overexpression lines. In agreement with the transcriptomic data, bbx29 mutant plants accumulated lower levels of kaempferol glucosides, sinapoyl malate, indol-3-ylmethyl glucosinolate (I3M), 4-methylsulfinylbutyl glucosinolate (4MSOB) and 3-methylthiopropyl glucosinolate (3MSP) in rosette leaves compared to the wild-type, and showed increased susceptibility to the necrotrophic fungus Botrytis cinerea and to the herbivore Spodoptera frugiperda. In contrast, BBX29 overexpressing plants displayed increased resistance to both attackers. In addition, we found that AtBBX29 plays an important role in mediating the effects of ultraviolet-B (UV-B) radiation on plant defense against B. cinerea. Taken together, these results suggest that AtBBX29 orchestrates the accumulation of specific light-induced metabolites and regulates Arabidopsis resistance against pathogens and herbivores.Graphical

Involvement of a receptor-like kinase complex of FvFLS2 and FvBAK1 in brassinosteroids-induced immunity in postharvest strawberry fruit

Conserved pathogen-derived features of microbial invaders are sensed by plants via pattern-recognition receptors (PRRs) and induce both local and systemic immune responses. The plant PRR flagellin sensitive 2 (FLS2), a leucine-rich repeat-receptor kinase, recognizes pathogen-derived molecules and initiates pattern-triggered immunity (PTI) responses by associating with other potential kinases to propagate downstream signalling cascades. Here, we identified a plasma membrane-localized receptor-like kinase BAK1 from strawberry (FvBAK1) that is rapidly induced upon exposure to the plant-specific hormone brassinosteroid (BR), which provides strawberry fruit with immunity to the necrotrophic fungus Botrytis cinerea. FvBAK1 reciprocally interacts with FvFLS2 and the receptor-like cytoplasmic kinase FvBIK1 in yeast cells in vivo. Subsequently, FvBIK1 can directly interact with respiratory burst oxidase homologue D (FvRBOHD), contributing to FvRBOHD-dependent ROS accumulation to amplify the SA signalling pathway in the BR-stimulated immunity of postharvest strawberry fruit to B. cinerea infection. Importantly, overexpression of bak1 promotes ROS accumulation and BR-induced defence responses, whereas bak1 loss-of-function mutants have compromised BR-induced SA signalling and immunity to necrotrophic fungal pathogens. In such a situation, FvBAK1 is an essential component of BR-mediated PTI signalling, which links the pathogen-derived receptor complex to downstream intracellular signalling pathways. Taken together, the findings of the current study highlight the importance of FvBAK1 as an upstream regulator of FvBIK1 and as a coreceptor of FvFLS2 in establishing BR-induced PTI signalling in postharvest strawberry fruit.

Tomato receptor-like cytoplasmic kinase Fir1 is involved in flagellin signaling and preinvasion immunity.

Detection of bacterial flagellin by the tomato (Solanum lycopersicum) receptors Flagellin sensing 2 (Fls2) and Fls3 triggers activation of pattern-triggered immunity (PTI). We identified the tomato Fls2/Fls3-interacting receptor-like cytoplasmic kinase 1 (Fir1) protein that is involved in PTI triggered by flagellin perception. Fir1 localized to the plasma membrane and interacted with Fls2 and Fls3 in yeast (Saccharomyces cerevisiae) and in planta. CRISPR/Cas9-generated tomato fir1 mutants were impaired in several immune responses induced by the flagellin-derived peptides flg22 and flgII-28, including resistance to Pseudomonas syringae pv. tomato (Pst) DC3000, production of reactive oxygen species, and enhanced PATHOGENESIS-RELATED 1b (PR1b) gene expression, but not MAP kinase phosphorylation. Remarkably, fir1 mutants developed larger Pst DC3000 populations than wild-type plants, whereas no differences were observed in wild-type and fir1 mutant plants infected with the flagellin deficient Pst DC3000ΔfliC. fir1 mutants failed to close stomata when infected with Pst DC3000 and Pseudomonas fluorescens and were more susceptible to Pst DC3000 than wild-type plants when inoculated by dipping, but not by vacuum-infiltration, indicating involvement of Fir1 in preinvasion immunity. RNA-seq analysis detected fewer differentially expressed genes in fir1 mutants and altered expression of jasmonic acid (JA)-related genes. In support of JA response deregulation in fir1 mutants, these plants were similarly susceptible to Pst DC3000 and to the coronatine-deficient Pst DC3118 strain, and more resistant to the necrotrophic fungus Botrytis cinerea following PTI activation. These results indicate that tomato Fir1 is required for a subset of flagellin-triggered PTI responses and support a model in which Fir1 negatively regulates JA signaling during PTI activation.

SlS5H silencing reveals specific pathogen-triggered salicylic acid metabolism in tomato

BackgroundSalicylic acid (SA) is a major plant hormone that mediates the defence pathway against pathogens. SA accumulates in highly variable amounts depending on the plant-pathogen system, and several enzyme activities participate in the restoration of its levels. Gentisic acid (GA) is the product of the 5-hydroxylation of SA, which is catalysed by S5H, an enzyme activity regarded as a major player in SA homeostasis. GA accumulates at high levels in tomato plants infected by Citrus Exocortis Viroid (CEVd), and to a lesser extend upon Pseudomonas syringae DC3000 pv. tomato (Pst) infection.ResultsWe have studied the induction of tomato SlS5H gene by different pathogens, and its expression correlates with the accumulation of GA. Transient over-expression of SlS5H in Nicotiana benthamiana confirmed that SA is processed by SlS5H in vivo. SlS5H-silenced tomato plants were generated, displaying a smaller size and early senescence, together with hypersusceptibility to the necrotrophic fungus Botrytis cinerea. In contrast, these transgenic lines exhibited an increased defence response and resistance to both CEVd and Pst infections. Alternative SA processing appears to occur for each specific pathogenic interaction to cope with SA levels. In SlS5H-silenced plants infected with CEVd, glycosylated SA was the most discriminant metabolite found. Instead, in Pst-infected transgenic plants, SA appeared to be rerouted to other phenolics such as feruloyldopamine, feruloylquinic acid, feruloylgalactarate and 2-hydroxyglutarate.ConclusionUsing SlS5H-silenced plants as a tool to unbalance SA levels, we have studied the re-routing of SA upon CEVd and Pst infections and found that, despite the common origin and role for SA in plant pathogenesis, there appear to be different pathogen-specific, alternate homeostasis pathways.

Nutrient Elements Promote Disease Resistance in Tomato by Differentially Activating Immune Pathways.

Nutrient elements play essential roles in plant growth, development, and reproduction. Balanced nutrition is critical for plant health and the ability to withstand biotic stress. Treatment with essential elements has been shown to induce disease resistance in certain cases. Understanding the functional mechanisms underlying plant immune responses to nutritional elements has the potential to provide new insights into crop improvement. In the present study, we investigated the effect of various elements-potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)-in promoting resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Xanthomonas euvesicatoria in tomato. We demonstrate that spray treatment of essential elements was sufficient to activate immune responses, inducing defense gene expression, cellular leakage, reactive oxygen species, and ethylene production. We report that different defense signaling pathways are required for induction of immunity in response to different elements. Our results suggest that genetic mechanisms that are modulated by nutrient elements can be exploited in agricultural practices to promote disease resistance.