Localization of probe-accessible chitin and characterization of genes encoding chitin-binding domains during rice-Magnaporthe oryzae interactions

Abstract

We examined the localization of probe-accessible chitin in Magnaporthe oryzae, which causes rice blast disease, during the early infection process and the functions of two genes encoding a chitin-binding domain (ChBD). Invasive hyphae in the first-invaded rice cell showed little staining with fluorescently labeled wheat germ agglutinin, a probe to detect chitin. However, in the second-invaded cell, hyphae showed strong fluorescence, and treatment with chitinase diminished the signal. Fourteen ChBD genes encoding family 18 carbohydrate-binding module (CBM18) were isolated from a Japanese strain of M. oryzae, Ina86-137. Reverse transcription-polymerase chain reaction analysis demonstrated that ChBD-1, ChBD-6, ChBD-8, ChBD-13, and ChBD-15 are expressed in the rice sheath. Gene-targeted disruptants of ChBD-1 and ChBD-15 had no significant differences in invasive growth, pathogenicity, or tolerance to chitinase compared to the wild type. These results suggest that M. oryzae has a mechanism to evade being a substrate for the host chitinase in the first-invaded cell, but neither ChBD-1 nor ChBD-15 contributes to this mechanism. © 2011 The Author(s).