A common toxin fold mediates microbial attack and plant defense

Area of Science:

• Plant Pathology
• Microbiology
• Structural Biology

Background:

• Plant pathogens utilize toxins to kill host cells, enhancing virulence.
• Necrosis and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs) are secreted by diverse bacteria, fungi, and oomycetes.
• NLPs induce necrosis and activate plant immunity.

Purpose of the Study:

• To determine the crystal structure of an NLP from Pythium aphanidermatum.
• To investigate the structural conservation and functional role of NLPs across different microbial taxa.
• To elucidate the mechanism by which NLPs contribute to plant pathogenesis and trigger plant defense responses.

Main Methods:

• Crystal structure determination of an NLP from Pythium aphanidermatum at 1.35Å resolution.
• Computational modeling of NLPs from Phytophthora parasitica and Pectobacterium carotovorum.
• Functional analysis through expression of oomycete NLPs in an NLP-deficient bacterial strain and analysis of NLP mutant proteins.

Main Results:

• The NLP structure revealed similarities to cytolytic toxins from marine organisms (actinoporins).
• High structural fold conservation was observed among NLPs from oomycetes and bacteria, indicating orthology.
• Identical structural properties are essential for NLP-mediated plasma membrane permeabilization, cytolysis, and restoration of bacterial virulence.
• NLP phytotoxicity and plant defense gene induction share common structural requirements.

Conclusions:

• NLPs are exceptionally conserved virulence factors with a broad taxonomic distribution.
• NLPs contribute to host infection by destroying the plant plasma membrane and causing cytolysis.
• Toxin-induced damage to host cell integrity triggers plant defense responses, suggesting a conserved mechanism in innate immunity across kingdoms.