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

Abstract

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.

Characteristics, Roles and Applications of Proteinaceous Elicitors from Pathogens in Plant Immunity

“…Necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) constitute another group of proteinaceous elicitors widely secreted by bacteria, fungi, and oomycetes. NLPs contain characteristic NPP1 domains (PF05630) and are involved in multiple processes such as virulence, conidiospore production, formation of appressoria, abiotic stresses in microbes and triggering immune responses in plants [ 11 , 13 , 58 , 74 , 75 ]. On the basis of their impacts on host plants, NLPs are classified into two forms: cytotoxic to eudicot and monocot plants and noncytotoxic [ 59 , 65 , 76 ].…”

“…In addition to NLPs functioning as PFTs, noncytotoxic NLPs and conserved fragments function as PAMPs/MAMPs to prime innate immunity in plants. Exogenous NLP or NLP fragment treatment or ectopic expression of NLP or conserved fragments (nlp20/nlp24) triggers plant immune responses, such as the expression of immune-responsive genes, activation of MAPK signaling cascades, bursts in ROS production, induction of SA, and enhanced plant immunity against pathogens in addition to necrosis and ethylene-induction [ 13 , 63 , 65 , 74 , 83 , 84 , 85 ].…”

“…According to their chemical properties, elicitors can be classified into proteinaceous, carbohydrate, chemical-inducing elicitors, and so on. Exogenous proteinaceous elicitors are proteinaceous elicitors from microorganisms, especially pathogens, and they are involved in many processes, such as the virulence of pathogens, abiotic stresses and biotic stresses in plants [ 11 , 12 , 13 , 14 , 15 ]. Although many studies and reviews have focused their attention on the involvement of proteinaceous elicitors in plant innate immunity and abiotic stresses in past decades, there is a lack of up-to-date reviews on the characteristics and functions of proteinaceous elicitors.…”