Nitrogen starvation of the rice blast fungus Magnaporthe grisea may act as an environmental cue for disease symptom expression.

摘要

RNA samples were prepared from leaves of blast-infected rice plants at 24, 36, 48, 72 and 96 h after inoculation. These plants showed no disease symptoms until 96 h after inoculation, when lesions appeared in large numbers across the plant surface.When gene expression was analysed using hybridization techniques, data suggested that nitrogen starvation of M. grisea elicited the expression of a large number of genes which were expressed by the fungus when it grew in rice leaves, particularly at theonset of disease symptoms. Leaves suspended in a nitrate-starved crude filter extract (MM-N CFE) of M. grisea showed pronounced senescence after 48 h. Two independent mpg1- mutants showed unaltered MM-N CFE activity, suggesting that senescence-inductionis not associated with MPG1 expression. The senescence-inducing activity of MM-N CFE was not produced by mutant strains (npr1- or npr2-) with a defect in nitrogen metabolism and pathogenicity, which suggested the involvement of NPR1 and NPR2 genes in disease symptom expression.