Mstul, an APSES transcription factor, is required for appressorium-mediated infection in magnaporthe grisea

Abstract

The APSES protein family includes important tran-scriptional regulators of morphological processes in ascomycetes. We identified a deletion mutant of the APSES protein Mstul in Magnaporthe grisea that showed reduced conidiation and mycelial growth. Mstul formed a number of appressoria comparable to the wild type, although appressorium formation was delayed. In M. grisea, rapid transfer of conidial glycogen and lipid droplets to incipient appressoria is required for appres-sorial turgor generation, which the fungus uses to penetrate plant cuticles. Appressorial turgor was low in mstul and the mutant was deficient in appressorium-mediated invasion of rice leaves. The transfer of conidial glycogen and lipid droplets was remarkably delayed in mstul, and a consequent delay in degrActation of these conidial reserves was observed. Our results indicate that Mstul is required for appressorium-mediated infection due to its involvement in the mobilization of lipids and glycogen.