S3: Elucidation of the role of NLPs of Verticillium longisporum infecting crucifers

Petr Karlovsky & Zhang Yuelin
PhD student: Ling Su

NLPs (Nep1-like proteins) are small proteins secreted by phytopathogenic bacteria, fungi and oomycetes into plant tissue. Some NLPs are cytotoxic; both cytotoxic and non-toxic NLPs trigger programmed cell death and innate immune response in plants.

V. longisporum is a merodiploid fungal pathogen adapted to crucifers. The genome of V. lonisporum contains NLP genes originating from both haploid ancestors (unpublished results of BioFung consortium in Göttingen). We determined in planta expression of five NLP genes of V. longisporum, purified the product of one of them, designated VlNEP-1, and characterized its cytotoxic activity. V. longisporum strains with VlNEP-1 silenced by RNAi caused less stunting in B. napus than the wildtype strain. The product of VlNEP-1 was detected in shoots of B. napus while the pathogen was still confined to hypocotyl. We hypothesize that NLPs released into xylem destroy the cell integrity in surrounding tissues, resulting in leakage of metabolites which then serve as nutrients for the pathogen. We further hypothesize that tissue destruction lead to stunting and is the cause of compensatory differentiation of xylem tissue, which our colleagues in Volker Lipka's laboratory recently discovered in plants infected with V. longisporum.

Our project pursues objectives related to the function of NLPs in plant infection and to the adaptation of V. longisporum to cruciferous hosts:

+ Test the hypothesis about disintegration of xylem-surrounding tissue and leakage of metabolites due to NLPs of V. longisporum transported in xylem ahead of the pathogen

+ Identify NLP genes of V. longisporum that are not expressed during infection, express them in a suitable host and purify their products

+ Comparison of the effect of NLPs expressed and not expressed during infection on plant defense pathways and on the outcome of V. longisporum infection