Cell wall integrity is crucial for fungal growth, development and stress survival. In yeast, Slt2MAP kinase and calcineurin signaling pathways monitor cell wall repair during stress and development. MPS1, the M. grisea SLT2 orthologue, is essential for cell wall repair and for appressorium mediated penetration into host plants (Xu 1998 PNAS 95:12713). In yeast, Slt2 activates the transcription factors Rlm1, Swi4 and Swi6, while calcineurin activates Crz1. Genes orthologous to yeast CRZ1, MPS1, RLM1, SWI4, and SWI6 genes were identified in M. grisea genome. Swi4 and Swi6 interact with Mps1 in yeast two hybrid assays. Deletion mutants were constructed by targeted gene replacement in M. grisea. Delta-mps1 mutants displayed an abnormal mycelial growth (no aerial hyphae), did not sporulate, and were nonpathogenic on plants as reported. Delta-crz1, delta-rlm1, delta-swi6 mutants have a normal mycelial growth and sporulation rates similar to wild type. Of these three mutants, only delta- Rlm1 displays a highly reduced pathogenicity on barley and rice (-98%, lesion number). Delta-mps1 mutants are highly sensitive to nikkomycin Z (chitin synthase inhibitor), CFW (disorganization of cell wall) and aculeacine (glucan synthase inhibitor), while delta-crz1 and delta-rlm1 mutant are only mildly hypersensitive to Nikkomycin, and delta-swi6 mutant is only slightly hypersensitive to CFW. These studies suggest that the transcription factors controlled by Mps1 are either functionally redundant or specialized in the control of specific target genes.