Functional analysis of a fungal endophyte stress-activated MAP kinase

The ability of fungi to sense and respond rapidly to environmental stress is crucial for their survival in the wild. One of the most important pathways involved in this response is the stress-activated MAP (mitogen-activated protein) kinase pathway. We report here on the isolation of the stress-activated MAP kinase, sakA, from the fungal endophyte Epichloe festucae. Complementation of the stress sensitivity and cell cycle defects of an Schizosaccharomyces pombe sty1Δ mutant with sakA confirmed it encodes a functional MAP kinase. Analysis of an E. festucae ΔsakA mutant revealed sakA is essential for growth under conditions of temperature and osmotic stress in culture, and for sensitivity to the fungicide fludioxonil. However, the ΔsakA mutant shows no increased sensitivity to hydrogen peroxide. Given sakA can rescue the sty1Δ mutant from sensitivity to oxidative stress, SakA has the potential to sense and transduce oxidative stress signals. The ΔsakA mutant is also defective in conidia formation, suggesting a role for SakA in asexual development of E. festucae. The detection of elevated hydrogen peroxide production in the ΔsakA mutant suggests there may be a link between MAP kinase and ROS (reactive oxygen species) signalling pathways in E. festucae.