Identification and characterization of apf1- in a non-pathogenic mutant of the rice blast fungus Magnaporthe grisea which is unable to differentiate appressoria

摘要

A spontaneous mutant was identified in a cross between 2 isolates of Magnaporthe grisea. The mutant was non-pathogenic on rice, and did not differentiate appressoria on hydrophobic surfaces. It was also non-pathogenic when inoculated on wounded leaves, suggesting that its ability to grow in plant tissue was also impaired. Mutant spores were 3-celled, with apical cells longer than those of parental isolates. Using one full sib-cross and one back-cross, it was demonstrated that all of the mutant phenotypes co-segregated as a single gene, named APF1. Comparison of apf1- mutants with previously characterized appressorium-deficient mutants of M. grisea provided evidence that APF1 is a new gene involved in appressorium differentiation, with pleiotropiceffects on plant colonisation and spore morphology. The apf1- mutants did not form appressoria in the presence of cyclic AMP, suggesting that APF1 acts downstream or independently of the cAMP signalling pathway required for appressorium differentiation and function in M. grisea.