Effects of Bioinsecticidal Aegerolysin-Based Cytolytic Complexes on Non-Target Organisms

Protein complexes from edible mushrooms as a sustainable potato protection against coleopteran pests

Protein complexes from edible oyster mushrooms (Pleurotus sp.) composed of pleurotolysin A2 (PlyA2) and pleurotolysin B (PlyB) exert toxicity in feeding tests against Colorado potato beetle (CPB) larvae, acting through the interaction with insect-specific membrane sphingolipid. Here we present a new strategy for crop protection, based on in planta production of PlyA2/PlyB protein complexes, and we exemplify this strategy in construction of transgenic potato plants of cv Désirée. The transgenics in which PlyA2 was directed to the vacuole and PlyB to the endoplasmic reticulum are effectively protected from infestation by CPB larvae without impacting plant performance. These transgenic plants showed a pronounced effect on larval feeding rate, the larvae feeding on transgenic plants being on average five to six folds lighter than larvae feeding on controls. Further, only a fraction (11%-37%) of the larvae that fed on transgenic potato plants completed their life cycle and developed into adult beetles. Moreover, gene expression analysis of CPB larvae exposed to PlyA2/PlyB complexes revealed the response indicative of a general stress status of larvae and no evidence of possibility of developing resistance due to the functional inactivation of PlyA2/PlyB sphingolipid receptors.

PriA is involved in Pleurotus ostreatus development and defense against Pseudomonas tolaasii

Pleurotus ostreatus is a crucial commercial mushroom widely cultivated for diverse uses. Scientists have worked on breeding disease-resistant and high-yielding varieties to secure food supply. Studies on the molecular genetic mechanism of growth and development can provide valuable information to facilitate crop breeding programs by genetic engineering. Aegerolysins are pore-forming proteins widely distributed in both prokaryotes and eukaryotes, which are reported to have haemolytic activity and be involved in the early stages of fructification. The present study aimed to explore biological function of a differential expressed aegerolysin gene PriA in P. ostreatus. The expression level of PriA gene was higher in primordium and fruiting body than that in mycelium. The PriA expression in overexpression (OE) and RNAi interference (RNAi) strains was detected by qRT-PCR. The RNAi strains grew at slightly slower rates and advanced producing yellow pigments than the wild type, while OE strains showed no prominent phenotypic characteristics. Furthermore, Pseudomonas tolaasii infection assays showed that the PriA OE strains could enhance mycelia and caps resistance to P. tolaasii. These data demonstrate PriA from P. ostreatus play an essential role in mycelial development and increase antagonism against P. tolaasii. Our study provides some reference information on interactions between edible fungi and pathogenic bacteria and offers a new resistance-conferring gene for breeding.

Assessing the toxicity of aegerolysin-based bioinsecticidal complexes using the sea urchin Paracentrotus lividus as model organism

The use of alternative solutions for pest management to replace pesticides in agriculture is of great interest. Proteinaceous complexes deriving from edible oyster mushrooms were recently proposed as environmentally friendly bioinsecticides. Such complexes, composed of ostreolysin A6 (OlyA6) and pleurotolysin B (PlyB), target invertebrate-specific membrane sphingolipids in insect's midgut, causing death through the formation of transmembrane pores. In this work, the potential impact of OlyA6/PlyB complexes was tested in the Mediterranean sea urchin Paracentrotus lividus, as an indicator of environmental quality. The ability of the fluorescently tagged OlyA6 to bind sea urchin gametes (sperm, eggs), the lipidome of sea urchin gametes, and the potential toxic effects and developmental anomalies caused by OlyA6/PlyB complexes on P. lividus early development (embryo, larvae) were investigated. The binding of the fluorescently tagged OlyA6 could be observed only in sea urchin eggs, which harbor OlyA6 sphingolipid membrane receptors, conversely to sperm. High protein concentrations affected sea urchin fertilization (>750 µg/L) and early development (> 375 µg/L in embryos; >100 µg/L in larvae), by causing toxicity and morphological anomalies in embryos and larvae. The main anomalies consisted in delayed embryos and incorrect migration of the primary mesenchyme cells that caused larval skeletal anomalies. The classification of these anomalies indicated a slight environmental impact of OlyA6/PlyB complexes at concentrations higher than 750 µg/L. Such impact should not persist in the marine environment, due to the reversible anomalies observed in sea urchin embryos and larvae that may promote defense strategies. However, before promoting the use of OlyA6/PlyB complexes as bio-pesticides at low concentrations, further studies on other marine coastal species are needed.

A single point mutation expands the applicability of ostreolysin A6 in biomedicine

An aegerolysin protein ostreolysin A6 (OlyA6) binds to cholesterol-complexed sphingomyelin and can be used for specific labelling of lipid rafts. In addition, OlyA6 interacts with even higher affinity with ceramide phosphoethanolamine (CPE), a sphingolipid that dominates in invertebrate cell membranes. In the presence of pleurotolysin B, a protein bearing the membrane-attack complex/perforin domain, OlyA6 forms pores in insect midgut cell membranes and acts as a potent bioinsecticide. It has been shown that a point mutation of glutamate 69 to alanine (E69A) allows OlyA6 to bind to cholesterol-free sphingomyelin. Using artificial lipid membranes and mammalian MDCK cells, we show that this mutation significantly enhances the interaction of OlyA6 with sphingomyelin and CPE, and allows recognition of these sphingolipids even in the absence of cholesterol. Our results suggest that OlyA6 mutant E69A could serve as complementary tool to detect and study cholesterol-associated and free sphingomyelin or CPE in membranes. However, the mutation does not improve the membrane-permeabilizing activity after addition of pleurotolysin B, which was confirmed in toxicity tests on insect and mammalian cell lines, and on Colorado potato beetle larvae.

Towards Understanding the Function of Aegerolysins

Aegerolysins are remarkable proteins. They are distributed over the tree of life, being relatively widespread in bacteria and fungi, but also present in some insects, plants, protozoa, and viruses. Despite their abundance in cells of certain developmental stages and their presence in secretomes, only a few aegerolysins have been studied in detail. Their function, in particular, is intriguing. Here, we summarize previously published findings on the distribution, molecular interactions, and function of these versatile aegerolysins. They have very diverse protein sequences but a common fold. The machine learning approach of the AlphaFold2 algorithm, which incorporates physical and biological knowledge of protein structures and multisequence alignments, provides us new insights into the aegerolysins and their pore-forming partners, complemented by additional genomic support. We hypothesize that aegerolysins are involved in the mechanisms of competitive exclusion in the niche.

Towards a Fungal Science That Is Independent of Researchers’ Gender

The main drivers of gender mainstreaming in basic and clinical research appear to be funding agencies and scientific journals. Some funding agencies have already recognized the importance of their actions for the global development of ideas in science, but further targeted efforts are needed. The challenges for women scientists in fungal research appear to be similar to those in other science, technology, engineering, and mathematics disciplines, although the gender gap in mycology publishing appears to be less pronounced; however, women are underrepresented as last (corresponding) authors. Two examples of best practices to bridge the gap have been promoted in the fungal community: “power hour” and a central resource database for women researchers of fungi and oomycetes. A more balanced ratio of women researchers among (plenary) session speakers, (plenary) session chairs, and committee members at the recent fungal genetics conference is an encouraging sign that the gender gap can be closed. The editorial policy of some journals follows the guidance “Sex and Gender Equality in Research,” and other journals should follow, and indicate the gender ratio among authors and reviewers.

Lipid-Binding Aegerolysin from Biocontrol Fungus Beauveria bassiana

Fungi are the most common pathogens of insects and thus important regulators of their populations. Lipid-binding aegerolysin proteins, which are commonly found in the fungal kingdom, may be involved in several biologically relevant processes including attack and defense against other organisms. Aegerolysins act alone or together with membrane-attack-complex/perforin (MACPF)-like proteins to form transmembrane pores that lead to cell lysis. We performed an in-depth bioinformatics analysis of aegerolysins in entomopathogenic fungi and selected a candidate aegerolysin, beauveriolysin A (BlyA) from Beauveria bassiana. BlyA was expressed as a recombinant protein in Escherichia coli, and purified to further determine its functional and structural properties, including lipid-binding ability. Aegerolysins were found to be encoded in genomes of entomopathogenic fungi, such as Beauveria, Cordyceps, Metarhizium and Ophiocordyceps. Detailed bioinformatics analysis revealed that they are linked to MACPF-like genes in most genomes. We also show that BlyA interacts with an insect-specific membrane lipid. These results were placed in the context of other fungal and bacterial aegerolysins and their partner proteins. We believe that aegerolysins play a role in promoting the entomopathogenic and antagonistic activity of B. bassiana, which is an active ingredient of bioinsecticides.