A common toxin fold mediates microbial attack and plant defense.

Many plant pathogens secrete toxins that enhance microbial virulence by killing host cells. Usually, these toxins are produced by particular microbial taxa, such as bacteria or fungi. In contrast, many bacterial, fungal and oomycete species produce necrosis and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) that trigger leaf necrosis and immunity-associated responses in various plants.

Inducible expression of a Nep1-like protein serves as a model trigger system of camalexin biosynthesis.

Camalexin, the major Arabidopsis phytoalexin, is synthesized in response to a great variety of pathogens. Specific pathogen-associated molecular patterns, such as Nep1-like proteins from oomycetes act as signals triggering the transcriptional activation of the camalexin biosynthetic genes. PaNie, a Nep1-like protein from Pythiumaphanidermatum was expressed in Arabidopsis under the control of an ethanol-inducible promoter.

Purification, crystallization and preliminary X-ray diffraction analysis of an oomycete-derived Nep1-like protein.

The elicitor protein Nep1-like protein from the plant pathogen Pythium aphanidermatum was purified and crystallized using the hanging-drop vapour-diffusion method. A native data set was collected to 1.35 A resolution at 100 K using synchrotron radiation.

Phytotoxicity and innate immune responses induced by Nep1-like proteins.

We show that oomycete-derived Nep1 (for necrosis and ethylene-inducing peptide1)-like proteins (NLPs) trigger a comprehensive immune response in Arabidopsis thaliana, comprising posttranslational activation of mitogen-activated protein kinase activity, deposition of callose, production of nitric oxide, reactive oxygen intermediates, ethylene, and the phytoalexin camalexin, as well as cell death. Transcript profiling experiments revealed that NLPs trigger extensive reprogramming of the Arabidopsis transcriptome closely resembling that evoked by bacteria-derived flagellin. NLP-induced cell death is an active, light-dependent process requiring HSP90 but not caspase activity, salicylic acid, jasmonic acid, ethylene, or functional SGT1a/SGT1b.