Lipid-flipping protein emerges as hidden master switch in rice blast fungus

The rice blast fungus Magnaporthe oryzae is one of the most destructive plant pathogens on Earth, stripping away roughly six percent of the global rice harvest every year, with individual epidemics capable of destroying up to thirty percent of yields in affected regions. For decades, researchers have dissected the molecular arsenal this fungus uses to invade rice tissue, yet many of the fundamental logistics of infection — how the pathogen moves proteins and lipids to the right place at the right time — have remained stubbornly opaque. Now a team of researchers working at Fujian Agriculture and Forestry University, together with collaborators at the Chinese Academy of Agricultural Sciences, Huazhong Agricultural University, and Ahmadu Bello University, has identified a single membrane protein that appears to sit at the very center of that logistics network. Their study, published in Stress Biology, shows that a lipid flippase called MoNeo1 acts as a central hub connecting membrane lipid chemistry to the vesicle trafficking machinery the fungus needs to grow, reproduce, and attack its host.

MoNeo1 belongs to a family of enzymes known as P4-ATPases, or phospholipid flippases. These molecular pumps perform a deceptively simple but profoundly important task: they grab specific phospholipids from the outer, luminal leaflet of a cellular membrane and flip them to the inner, cytosolic leaflet. In doing so, they create what biologists call lipid asymmetry — a deliberate imbalance in the distribution of phospholipids between the two faces of a membrane. That asymmetry is not a cosmetic detail. It changes the physical properties of the membrane, curvature, charge, and fluidity, and it is a prerequisite for the budding of transport vesicles from the trans-Golgi network and endosomal membranes. In budding yeast, the Neo1 protein is essential for life; in humans, mutations in the Neo1 ortholog ATP9A are linked to hypotonia, intellectual disability, and attention deficit hyperactivity disorder. Until now, however, the role of this conserved flippase in plant-pathogenic fungi had not been systematically explored.

The team began by searching the M. oryzae genome for a counterpart of the well-characterized yeast Neo1. A BLAST search against the Kyoto Encyclopedia of Genes and Genomes returned a single strong candidate, the product of gene MGG_04066, which shares 55.28 percent amino acid identity with its yeast ortholog across eighty percent of the protein length. Phylogenetic analysis confirmed that Neo1 is tightly conserved across filamentous fungi, clustering closely with homologs from Botrytis cinerea and Aspergillus oryzae. Structural predictions generated with AlphaFold2, refined against known homologous structures, revealed the canonical P4-ATPase architecture: a transmembrane domain embedded in the lipid bilayer, flanked by the actuator, nucleotide-binding, and phosphorylation domains that together drive the ATP-powered flipping cycle. In short, MoNeo1 looked every bit the genuine flippase, and the researchers were ready to ask what happens when it is removed.

The answer, obtained through targeted gene deletion by homologous recombination, was dramatic. The ΔMoneo1 mutant remained viable — unlike its yeast counterpart — but its growth was visibly stunted across four different culture media compared with the wild-type Guy11 strain and a genetically complemented control. More striking still was the effect on asexual reproduction. Conidia, the spores through which rice blast spreads from plant to plant, were reduced by approximately 87.3 percent in the mutant, and the conidiophores that produce them developed abnormally. Because conidiation is the engine of disease persistence and dissemination in the field, this single defect would be enough to cripple an epidemic. Yet the most consequential phenotype emerged when the researchers turned their attention to infection itself.

M. oryzae initiates infection by germinating a conidium on the leaf surface and building a specialized dome-shaped structure called an appressorium, which generates enormous internal turgor pressure to mechanically breach the rice cuticle. In the ΔMoneo1 mutant, germ tubes elongated abnormally and appressorium formation was delayed, falling by more than fifty percent relative to the wild type at early time points, although the structures eventually formed by twenty-four hours. Formation, however, was not the same as function. Cytorrhysis assays, in which appressoria are challenged with increasing concentrations of glycerol to measure their internal pressure, revealed that mutant appressoria collapsed at significantly higher rates, indicating reduced turgor. Nile red staining showed impaired lipid retention at six and sixteen hours after induction, suggesting a failure in the glycerol generation that fuels the pressure build-up. Consistent with these functional deficits, the mutant produced far fewer invasive hyphae inside rice leaf sheaths, and blast symptoms on both barley leaves and susceptible CO39 rice seedlings were greatly reduced.

The mechanistic thread running through these phenotypes appears to be lipid chemistry. Quantitative lipidomics by high-performance liquid chromatography coupled to mass spectrometry revealed that deletion of MoNEO1 threw the fungus’s phospholipid economy into disarray. Levels of phosphatidylcholine rose by forty-two percent, phosphatidylethanolamine by thirty-eight percent, phosphatidylserine by twenty-one percent, and phosphatidylinositol by nineteen percent, while phosphatidic acid fell by twenty-eight percent and lysophosphatidylethanolamine by seventeen percent. Storage and signaling lipids shifted as well, with triacylglycerol increasing by twenty-three percent and diacylglycerol by fourteen percent. Nearly all of these changes were reversed in the complemented strain, confirming that they were specifically attributable to the loss of MoNeo1. The mutant was also hypersensitive to membrane stress induced by sodium chloride and Calcofluor White, consistent with a compromised membrane barrier. Together, the data paint MoNeo1 as a guardian of phospholipid homeostasis whose absence forces the cell into a compensatory rerouting of lipid metabolism.

Where does MoNeo1 do its work? Live-cell fluorescence microscopy of a MoNeo1-GFP fusion expressed under its native promoter showed the protein as discrete, motile puncta throughout the fungal life cycle. Co-expression with the trans-Golgi network marker MoKex2-mCherry revealed partial co-localization, and labeling of early endosomes with the dye FM4-64 showed transient overlap as well. MoNeo1, in other words, resides at the interface between the trans-Golgi network and the endosomal system — precisely the crossroads through which retrograde cargo traffic must pass. The team then asked how this steady-state distribution is maintained, focusing on the retromer, a conserved pentameric complex that retrieves membrane proteins from endosomes and returns them to the trans-Golgi network, thereby rescuing them from degradation in the vacuole. In yeast, Neo1 is a known retromer cargo, and the researchers suspected the same relationship might hold in M. oryzae.

It did. Co-immunoprecipitation experiments recovered MoNeo1-Flag together with MoVps35-GFP, the cargo-recognition core of the retromer, and live-cell imaging showed the two proteins traveling together on motile puncta through the hyphal cytoplasm. The dependency ran in one direction only: when MoVPS35 was deleted, MoNeo1-GFP vanished from its normal trans-Golgi and endosomal puncta and accumulated instead on the vacuolar membrane, in both vegetative hyphae and conidia. Deleting MoNEO1, by contrast, left the distribution of MoVps35 untouched. The retromer, therefore, sits upstream, continuously recycling MoNeo1 back to its functional address and protecting it from vacuolar degradation. This is a textbook retrograde trafficking relationship, now demonstrated for the first time in a major plant pathogen.

The final piece of the puzzle connects lipid flipping to the secretion of virulence proteins. Affinity purification and mass spectrometry of MoNeo1-Flag complexes identified 521 candidate interacting proteins, among them MoSnc1, an R-SNARE protein known to mediate effector secretion and to travel on the endosome-to-plasma-membrane route. Co-immunoprecipitation confirmed a physical interaction between MoNeo1 and MoSnc1, and the two proteins partially co-localized in living cells. Crucially, in the ΔMoneo1 mutant, the number and size of MoSnc1-positive puncta shrank, and the SNARE was progressively mis-sorted into the vacuole for degradation, while MoNeo1 localization remained normal in a ΔMosnc1 background. The consequence for virulence was direct: the apoplastic effector Bas4 accumulated abnormally in the cytosol and vacuole, and the cytoplasmic effector Pwl2 formed misplaced cytosolic foci instead of being delivered into host cells. The researchers propose that the membrane asymmetry generated by MoNeo1 creates lipid environments — rich in appropriately distributed phosphatidylserine and phosphatidylethanolamine — that are required for the stability, fusion competence, and recycling of MoSnc1-containing transport intermediates. Without that lipid scaffolding, the entire secretion pipeline that arms the fungus for invasion collapses. The study thus reframes MoNeo1 not as a housekeeping enzyme but as a strategic coordinator, integrating retrograde protein sorting with lipid translocation to support appressorium function and host penetration. Because flippases of this family are conserved across fungal pathogens, including the wheat scab fungus Fusarium graminearum and the human pathogen Cryptococcus neoformans, the pathway defined here offers a template for targeted disease control strategies that could protect rice yields without relying on conventional fungicides.

Subject of Research: Role of the P4-ATPase lipid flippase MoNeo1 in vesicle trafficking and pathogenicity of the rice blast fungus Magnaporthe oryzae

Article Title: The lipid flippase MoNeo1 mediates vesicle trafficking and pathogenicity in Magnaporthe oryzae

Article References: Cai, Y., Huang, X., Nie, Y., Luan, Y., Aarti, A., Gong, Q., Sun, P., Abubakar, Y. S., Wang, B., Wang, A., Li, G., Lin, L., & Zheng, W. (2026). The lipid flippase MoNeo1 mediates vesicle trafficking and pathogenicity in Magnaporthe oryzae. Stress Biology, 6(1), Article 28. https://doi.org/10.1007/s44154-026-00305-5

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00305-5

Keywords: Magnaporthe oryzae, rice blast, lipid flippase, P4-ATPase, MoNeo1, vesicle trafficking, retromer, MoVps35, MoSnc1, SNARE, effector secretion, appressorium