Identification and characterization of the Nep1-like protein UvNLP in rice false smut fungus Ustilaginoidea virens

Background The necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) are a broadly distributed superfamily of protiens in plant-associated microorganisms, including bacteria, fungi, and oomycetes. NLPs are considered to be important virulence factors, and some have been well studied. However, the role of NLPs in Ustilaginoidea virens , the agent of rice false smut fungus, remains to be uncovered.Results A protein containing NLP-specific NPP1 domain was identified in U. virens and named UvNLP. Phylogenetic analysis revealed that UvNLP was a type 2 NLP, and real-time PCR revealed that UvNLP was highly expressed at 3 days post-inoculation. A yeast secretion assay demonstrated that UvNLP contained a functional signal peptide (SP). Furthermore, transient expression of UvNLP in Nicotiana benthamiana induced weak cell death, and replacement of the SP enhanced cell death. Real-time PCR indicated that UvNLP induced the expression of plant defence related genes.Conclusions We identified a secreted protein UvNLP in U. virens that was infection related and could induce plant cell death and defence responses. This study provided evidence that NLPs act as proteinaceous MAMPs, giving insight into the elucidation of the pathogenicity mechanism of U. virens. The UvNLP might be used as a potential plant defence inducer for disease control in practice.