In-vitro and in-planta Botrytis cinerea Inoculation Assays for Tomato

Green light induces Solanum lycopersicum JA synthesis and inhibits Botrytis cinerea infection cushion formation to resist grey mould disease

Light signals are prevalent and influence the survival strategies of both plants and the pathogenic fungi that infect them. In this study, we found that green light inhibits the infectivity of Botrytis cinerea on Solanum lycopersicum. Through transcriptome analysis and validation of S. lycopersicum leaves infected with B. cinerea, we discovered that green light enhances the synthesis of jasmonic acid and its related metabolites by upregulating the expression of OPR3 and JAR1 in S. lycopersicum. Additionally, green light boosts the activity of antioxidant enzymes like peroxidase, catalase, and ascorbic acid peroxidase in S. lycopersicum to combat tomato grey mould. Conversely, green light inhibits the expression of plant-induced colonization onset genes, mitogen-activated protein kinase genes, and the formation of infection cushions in B. cinerea. Our findings provide insights into the role of environmental green light signals in the interaction system between plants and phytopathogenic fungi.

Antagonistic systemin receptors integrate the activation and attenuation of systemic wound signaling in tomato

Pattern recognition receptor (PRR)-mediated perception of damage-associated molecular patterns (DAMPs) triggers the first line of inducible defenses in both plants and animals. Compared with animals, plants are sessile and regularly encounter physical damage by biotic and abiotic factors. A longstanding problem concerns how plants achieve a balance between wound defense response and normal growth, avoiding overcommitment to catastrophic defense. Here, we report that two antagonistic systemin receptors, SYR1 and SYR2, of the wound peptide hormone systemin in tomato act in a ligand-concentration-dependent manner to regulate immune homeostasis. Whereas SYR1 acts as a high-affinity receptor to initiate systemin signaling, SYR2 functions as a low-affinity receptor to attenuate systemin signaling. The expression of systemin and SYR2, but not SYR1, is upregulated upon SYR1 activation. Our findings provide a mechanistic explanation for how plants appropriately respond to tissue damage based on PRR-mediated perception of DAMP concentrations and have implications for uncoupling defense-growth trade-offs.

Design, synthesis, and antifungal activity of novel pyrazole carboxamide derivatives containing benzimidazole moiety as potential SDH inhibitors

To address the urgent need for new antifungal agents, a collection of novel pyrazole carboxamide derivatives incorporating a benzimidazole group were innovatively designed, synthesized, and evaluated for their efficacy against fungal pathogens. The bioassay results revealed that the EC50 values for the compounds A7 (3-(difluoromethyl)-1-methyl-N-(1-propyl-1H-benzo[d]imidazol-2-yl)-1H-pyrazole-4-carboxamide) and B11 (N-(1-(4-chlorobenzyl)-1H-benzo[d]imidazol-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide) against B. cinerea were notably low to 0.79 µg/mL and 0.56 µg/mL, respectively, demonstrating the potency comparable to that of the control fungicide boscalid, which has an EC50 value of 0.60 µg/mL. Noteworthy is the fact that in vivo tests demonstrated that A7 and B11 showed superior protective effects on tomatoes and strawberries against B. cinerea infection when juxtaposed with the commercial fungicide carbendazim. The examination through scanning electron microscopy revealed that B11 notably alters the morphology of the fungal mycelium, inducing shrinkage and roughening of the hyphal surfaces. To elucidate the mechanism of action, the study on molecular docking and molecular dynamics simulations was conducted, which suggested that B11 effectively interacts with crucial amino acid residues within the active site of succinate dehydrogenase (SDH). This investigation contributes a novel perspective for the structural design and diversification of potential SDH inhibitors, offering a promising avenue for the development of antifungal therapeutics.

BcWRKY33A Enhances Resistance to Botrytis cinerea via Activating BcMYB51-3 in Non-Heading Chinese Cabbage

The transcription factor WRKY33 is a vital regulator of the biological process of the necrotrophic fungus Botrytis cinerea (B. cinerea). However, its specific regulatory mechanism remains to be further investigated. In non-heading Chinese cabbage (NHCC, Brassica campestris (syn. Brassica rapa) ssp. Chinensis), our previous study showed that BcWRKY33A is induced not only by salt stress, but also by B. cinerea infection. Here, we noticed that BcWRKY33A is expressed in trichomes and confer plant defense resistance. Disease symptoms and qRT-PCR analyses revealed that BcWRKY33A-overexpressing and -silencing lines were less and more severely impaired, respectively, than wild type upon B. cinerea treatment. Meanwhile, the transcripts’ abundance of indolic glucosinolates’ (IGSs) biosynthetic genes is consistent with plants’ B. cinerea tolerance. Identification and expression pattern analysis of BcMYB51s showed that BcMYB51-3 has a similar trend to BcWRKY33A upon B. cinerea infection. Moreover, BcWRKY33A directly binds to the BcMYB51-3 promoter, which was jointly confirmed by Y1H, dual-LUC, and EMSA assays. The importance of MYB51, the homolog of BcMYB51-3, in the BcWRKY33A-mediated B. cinerea resistance was also verified using the TRV-based VIGS system. Overall, our data concludes that BcWRKY33A directly activates the expression of BcMYB51-3 and downstream IGSs’ biosynthetic genes, thereby improving the B. cinerea tolerance of NHCC plants.

Stemphylium lycopersici Nep1-like Protein (NLP) Is a Key Virulence Factor in Tomato Gray Leaf Spot Disease

The fungus Stemphylium lycopersici (S. lycopersici) is an economically important plant pathogen that causes grey leaf spot disease in tomato. However, functional genomic studies in S. lycopersici are lacking, and the factors influencing its pathogenicity remain largely unknown. Here, we present the first example of genetic transformation and targeted gene replacement in S. lycopersici. We functionally analyzed the NLP gene, which encodes a necrosis- and ethylene-inducing peptide 1 (Nep1)-like protein (NLP). We found that targeted disruption of the NLP gene in S. lycopersici significantly compromised its virulence on tomato. Moreover, our data suggest that NLP affects S. lycopersici conidiospore production and weakly affects its adaptation to osmotic and oxidative stress. Interestingly, we found that NLP suppressed the production of reactive oxygen species (ROS) in tomato leaves during S. lycopersici infection. Further, expressing the fungal NLP in tomato resulted in constitutive transcription of immune-responsive genes and inhibited plant growth. Through gene manipulation, we demonstrated the function of NLP in S. lycopersici virulence and development. Our work provides a paradigm for functional genomics studies in a non-model fungal pathogen system.