Histidine kinases mediate differentiation, stress response, and pathogenicity in Magnaporthe oryzae

The aim of this study is a functional characterization of 10 putative histidine kinases (HIKs)-encoding genes in the phytopathogenic fungus Magnaporthe oryzae. Two HIKs were found to be required for pathogenicity in the fungus. It was found that the mutant strains Mohik5 and Mohik8 show abnormal conidial morphology and furthermore Mohik5 is unable to form appressoria. Both HIKs MoHik5p and MoHik8p appear to be essential for pathogenicity since the mutants fail to infect rice plants. MoSln1p and MoHik1p were previously reported to be components of the HOG pathway in M. oryzae. The Mosln1 mutant is more susceptible to salt stress compared to Mohik1, whereas Mohik1 appears to be stronger affected by osmotic or sugar stress. In contrast to yeast, the HOG signaling cascade in phytopathogenic fungi apparently comprises more elements. Furthermore, vegetative growth of the mutants Mohik5 and Mohik9 was found to be sensitive to hypoxia-inducing NaNO2-treatment. Additionally, it was monitored that NaNO2-treatment resulted in MoHog1p phosphorylation. As a consequence we assume a first simplified model for hypoxia signaling in M. oryzae including the HOG pathway and the HIKs MoHik5p and MoHik9p.