A fatty acid elongase complex regulates cell membrane integrity and septin-dependent host infection by the rice blast fungus.

Very-long-chain fatty acids (VLCFAs) regulate biophysical properties of cell membranes to determine growth and development of eukaryotes, such as the pathogenesis of the rice blast fungus Magnaporthe oryzae. The fatty acid elongase Elo1 regulates pathogenesis of M. oryzae by modulating VLCFA biosynthesis. However, it remains unknown whether and how Elo1 associates with other factors to regulate VLCFA biosynthesis in fungal pathogens. Here, we identified Ifa38, Phs1 and Tsc13 as interacting proteins of Elo1 by proximity labelling in M. oryzae. Elo1 associated with Ifa38, Phs1 and Tsc13 on the endoplasmic reticulum (ER) membrane to control VLCFA biosynthesis. Targeted gene deletion mutants Δifa38, Δphs1 and Δtsc13 were all similarly impaired as Δelo1 in vegetative growth, conidial morphology, stress responses in ER, cell wall and membrane. These deletion mutants also displayed severe damage in cell membrane integrity and failed to organize the septin ring that is essential for penetration peg formation and pathogenicity. Our study demonstrates that M. oryzae employs a fatty acid elongase complex to regulate VLCFAs for maintaining or remodelling cell membrane structure, which is important for septin-mediated host penetration.

Discovery of broad-spectrum fungicides that block septin-dependent infection processes of pathogenic fungi.

Many pathogenic fungi depend on the development of specialized infection structures called appressoria to invade their hosts and cause disease. Impairing the function of fungal infection structures therefore provides a potential means by which diseases could be prevented. In spite of this extraordinary potential, however, relatively few anti-penetrant drugs have been developed to control fungal diseases, of either plants or animals. In the present study, we report the identification of compounds that act specifically to prevent fungal infection. We found that the organization of septin GTPases, which are essential for appressorium-mediated infection in the rice blast fungus Magnaporthe oryzae, requires very-long-chain fatty acids (VLCFAs), which act as mediators of septin organization at membrane interfaces. VLCFAs promote septin recruitment to curved plasma membranes and depletion of VLCFAs prevents septin assembly and host penetration by M. oryzae. We observed that VLCFA biosynthesis inhibitors not only prevent rice blast disease, but also show effective, broad-spectrum fungicidal activity against a wide range of fungal pathogens of maize, wheat and locusts, without affecting their respective hosts. Our findings reveal a mechanism underlying septin-mediated infection structure formation in fungi and provide a class of fungicides to control diverse diseases of plants and animals.