An exo-1,3-β-glucanase GLU1 contributes to the virulence of the wheat tan spot pathogen Pyrenophora tritici-repentis

Tan spot, caused by Pyrenophora tritici-repentis, is an important foliar disease of wheat. In the present study, a gene named glucanase gene (GLU1) encoding a putative exo-1,3-β-glucanase was cloned from a race five isolate of P. tritici-repentis. Transcription profile analysis of the GLU1 gene showed a carbon source control of the accumulation of transcript, which is strongly induced in minimal medium but depressed in rich medium. A time-course study of the infection process of the wild-type isolate on a susceptible wheat genotype revealed that the transcript level of GLU1 increased more than 8000-fold 8 h after inoculation. To study its potential function in pathogenicity, GLU1 was silenced via a sense and antisense mediated silencing mechanism. One transformant named C1 showed significantly reduced growth and sporulation relative to the wild-type. Cytological analysis of the infection revealed that C1 produced significantly lower numbers of germ tubes and appressoria than the wild-type strain on susceptible wheat leaves. This strain, as well as another two transformants, caused significantly less disease symptoms relative to the wild-type after inoculation onto a susceptible wheat genotype. These results indicate that GLU1 contributes to the development and virulence of P. tritici-repentis.