A lectin gene is involved in the defense of Pleurotus ostreatus against the mite predator Tyrophagus putrescentiae

The storage mite, Tyrophagus putrescentiae, found worldwide in many habitats, is an important pest of edible mushrooms. Excessive chemical spraying for pest control has been linked to environmental pollution, health risks, insecticide resistance development, and food safety. Host resistance can be sustainable and cost-effective and provide effective and economical pest control. Previous studies have reported that the oyster mushroom Pleurotus ostreatus has evolved effective defense mechanisms against T. putrescentiae attack, but the underlying mechanism remains unclear. Here we report that a lectin gene from P. ostreatus mycelia, Polec2, induced fungal resistance to mite grazing. Polec2 belongs to a galectin-like lectin classification, encoding a protein with β-sandwith-fold domain. Overexpression of Polec2 in P. ostreatus led to activation of the reactive oxygen species (ROS)/mitogen-activated protein kinases (MAPKs) signaling pathway, salicylic acid (SA), and jasmonate (JA) biosynthesis. The activation resulted in bursts of antioxidant activities of catalases (CAT), peroxidases (POD), superoxide dismutases (SOD), and increased production of SA, JA, jasmonic acid-isoleucine (JA-Ile) and jasmonic acid methyl ester (MeJA), accompanied by reduced T. putrescentiae feeding and suppressed its population. We also provide an overview of the phylogenetic distribution of lectins across 22 fungal genomes. Our findings shed light on the molecular mechanisms of P. ostreatus' defense against the mite predator and will be useful in investigating the molecular basis of fungi-fungivory interactions and gene mining for pest-resistance genes.

Arabidopsis Toxicos en Levadura 12 (ATL12): A Gene Involved in Chitin-Induced, Hormone-Related and NADPH Oxidase-Mediated Defense Responses

Plants, as sessile organisms, have evolved complex systems to respond to changes in environmental conditions. Chitin is a Pathogen-Associated-Molecular Pattern (PAMP) that exists in the fungal cell walls, and can be recognized by plants and induce plant pattern-triggered immunity (PTI). Our previous studies showed that Arabidopsis Toxicos en Levadura 12 (ATL12) is highly induced in response to fungal infection and chitin treatment. We used the model organism Arabidopsis thaliana to characterize ATL12 and explore its role in fungal defense. Histochemical staining showed that pATL12-GUS was continually expressed in roots, leaves, stems, and flowers. Subcellular co-localization of the ATL12-GFP fusion protein with the plasma membrane-mcherry marker showed that ATL12 localizes to the plasma membrane. Mutants of atl12 are more susceptible to Golovinomyces cichoracearum infection, while overexpression of ATL12 increased plant resistance to the fungus. ATL12 is highly induced by chitin after two hours of treatment and ATL12 may act downstream of MAPK cascades. Additionally, 3,3'-diaminobenzidine (DAB) staining indicated that atl12 mutants generate less reactive oxygen species compared to wild-type Col-0 plants and RT-PCR indicated that ATL12-regulated ROS production may be linked to the expression of respiratory burst oxidase homolog protein D/F (AtRBOHD/F). Furthermore, we present evidence that ATL12 expression is upregulated after treatment with both salicylic acid and jasmonic acid. Taken together, these results suggest a role for ATL12 in crosstalk between hormonal, chitin-induced, and NADPH oxidase-mediated defense responses in Arabidopsis.

Identification of a Novel Nematotoxic Protein by Challenging the Model Mushroom Coprinopsis cinerea with a Fungivorous Nematode

The dung of herbivores, the natural habitat of the model mushroom Coprinopsis cinerea, is a nutrient-rich but also very competitive environment for a saprophytic fungus. We showed previously that C. cinerea expresses constitutive, tissue-specific armories against antagonists such as animal predators and bacterial competitors. In order to dissect the inducible armories against such antagonists, we sequenced the poly(A)-positive transcriptome of C. cinerea vegetative mycelium upon challenge with fungivorous and bacterivorous nematodes, Gram-negative and Gram-positive bacteria and mechanical damage. As a response to the fungivorous nematode Aphelenchus avenae, C. cinerea was found to specifically induce the transcription of several genes encoding previously characterized nematotoxic lectins. In addition, a previously not characterized gene encoding a cytoplasmic protein with several predicted Ricin B-fold domains, was found to be strongly upregulated under this condition. Functional analysis of the recombinant protein revealed a high toxicity toward the bacterivorous nematode Caenorhabditis elegans. Challenge of the mycelium with A. avenae also lead to the induction of several genes encoding putative antibacterial proteins. Some of these genes were also induced upon challenge of the mycelium with the bacteria Escherichia coli and Bacillus subtilis. These results suggest that fungi have the ability to induce specific innate defense responses similar to plants and animals.