Ca(2+) is a second messenger in pathways that transduce external signals and activate cellular processes in plants and animals. Ca(2+)-mediated signal transduction is involved in key pathways that contribute to a variety of fundamental physiological processes in eukaryotic cells. However, little is known about the molecular mechanisms of Ca(2+)-mediated signal transduction in filamentous fungi. In this study, the MoCMK1 gene, encoding a putative Ca(2+)/calmodulin-dependent kinase, was identified in the rice blast fungus Magnaporthe oryzae. Three MoCMK1 deletion mutants were obtained by a targeted gene replacement. Colonies of the MoCMK1 mutants had sparse aerial hyphae and fewer conidia than the wild-type strain on complete medium. Conidial germination and appressorial formation were delayed in the DeltaMocmk1 mutants. In spray inoculation tests, DeltaMocmk1 mutants exhibited a weakened ability to infect the susceptible rice cultivar CO-39, compared to the wild-type strain Guy11. These results showed that MoCMK1 plays key roles in the pathogenicity of the rice blast fungus.
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