Definition of tissue-specific and general requirements for plant infectionin a phytopathogenic fungus

Although plant diseases are usually characterized by the part of the plant that is affected (e.g., leaf spots, root rots, wilts), surprisingly little is known about the factors that condition the ability of pathogens to colon ize different plant tissues; Here we demonstrate that the leaf blast pathog en Magnaporthe grisea also can infect plant roots, and we exploit this find ing to distinguish tissue-specific and general requirements for plant infec tion. Tests of a M. grisea mutant collection identified some mutants that w ere defective specifically in infection of either leaves or roots, and othe rs such as the map kinase mutant pmk1 that were generally defective in path ogenicity. Conservation of a functional PMK1-related MAP-kinase in the root pathogen Gaeumannomyces graminis was also demonstrated, Exploitation of th e ability of M. grisea to infect distinct plant tissues thus represents a p owerful tool for the comprehensive dissection of genetic determinants of ti ssue specificity and global requirements for plant infection.