Dihydroxyhexanoic acid biosynthesis controls turgor in pathogenic fungi

Many plant pathogenic fungi penetrate host surfaces mechanically, using turgor pressure generated by specialized infection cells called appressoria. These appressoria develop semipermeable cell walls and accumulate osmolytes internally to create turgor by osmosis. Although melanin is known to be important for turgor generation, the mechanism underlying wall semipermeability remains unclear. By using reverse genetics, we identified that the enzymes PKS2 and PBG13 are required for forming the semipermeable barrier in fungi causing anthracnose and rice blast diseases. These enzymes synthesize 3,5-dihydroxyhexanoic acid polymers that are essential for pathogenicity. These polymers reduce cell wall permeability and generate turgor, independently of melanization. Our findings uncover a mechanism of fungal turgor generation, linking enzyme function to pathogen penetration and disease potential, presenting new targets for disease control.