Abstract

The rice blast fungus Magnaporthe grisea differentiates appressoria, which are required to attack its rice plant host. Clone A26, tentatively named LPL1, was previously found to be homologous to the known lysophospholipase genes from our subtractive cDNA library. The LPL1 protein had a consensus motif (GxSxG) and a catalytic triad (S, D, H) of esterases in the deduced amino acid sequence, and the protein expressed in Escherichia coli had lysophospholipase activity. To clarify the functions and possible roles of LPL1, the gene was disrupted by targeted gene replacement. The ĢLPL1 mutants formed fewer appressoria on the hydrophobic surface of GelBond film, and the appressoria had reduced turgor pressure and penetration into cells of the leaf sheath. The ĢLPL1 mutants and wild-type differentiated normal appressoria on other artificial substrata such as polycarbonate plate and on rice leaf sheath. Cytological analysis of the appressoria indicated that ĢLPL1 mutants had a delay in the disappearance of lipid droplets. These findings imply that LPL1, phospholipid metabolism, or both are involved in glycerol biosynthesis and accumulation to generate turgor pressure in the appressorium. LPL1 was, however, dispensable for full pathogenicity, suggesting that other complementary pathways or similar genes related to phospholipid metabolism probably function in M. grisea.
*Faculty of Science and Technology, Tokyo University of Science