MoLys2 is necessary for growth, conidiogenesis, lysine biosynthesis, and pathogenicity in Magnaporthe oryzae

Abstract

Amino acid biosyntheses are complex but essential processes in growth and differentiation of eukaryotic cells. In the budding yeast Saccharomyces cerevisiae, the lysine biosynthesis via the α-aminoadipate (AA) pathway involves several steps, including reduction of AA to AA 6-semialdehyde by AA reductase ScLys2. In filamentous fungus Penicillium chrysogenum, disruption of the LYS2 gene blocked the lysine biosynthesis but promoted the production of the secondary metabolite penicillin. In comparison, little is known about the function of AA reductase Lys2 in phytopathogenic fungi. We here characterized the functions of MoLys2, a homolog of ScLys2, from the rice blast fungus Magnaporthe oryzae. Our results showed that the ΔMolys2 mutants were auxotrophic for lysine. The ΔMolys2 mutants also exhibited drastic reduction in pathogenicity on rice, inducing small disease lesions. Microscopic examination of the lesions revealed that the invasive hyphae of ΔMolys2 mutants were mostly restricted to the primary infected leaf sheath cells. In addition, exogenous lysine restored the production of conidia and near wild-type appressoria differentiation, and rescued the defect of pathogenicity in conidia infection of detached barely and rice leaf sheath. Our results indicated that MoLys2 is necessary for lysine biosynthesis that affects growth, conidiogenesis, and pathogenicity of the fungus. This study does implicate the potential for targeting lysine biosynthesis for the development of novel fungicides against M. oryzae.