In the double mutant, expression of GLR1, for example, was about twofold lower than in Δchap1, reaching the level observed in the untreated WT control (no oxidant stress). In yeast, Yap1 and Skn7 coregulate some oxidative stress response genes (He et al., 2009), and our data provide

the first genetic evidence, to our knowledge, that this Inhibitor Library mechanism acts in a filamentous fungus. Significantly, in the double mutant GLR1, TRX2 and SOD1 are not induced at all (Fig. 2). Thus, although Skn7 is not absolutely required for ChAP1 function, the combined contribution of both ChAP1 and Skn7 is needed for expression of GLR1, TRX2, and SOD1 in response to oxidant stress. The low transcript levels remaining in oxidant-stressed Δchap1 (Fig. 2) could still provide significant amounts of enzyme activity. Complete loss, in the double mutant,

of oxidant-induced expression of some genes needed to cope with oxidative stress would imply that the ChAP1-dependent ROS detoxifying mechanism is severely impaired when Skn7 is absent. This prediction can be further tested at the protein abundance or enzyme activity levels. Skn7 control was most evident for the superoxide dismutase encoding gene SOD1, where ChAP1 control is minor if at all (Fig. 2). In Candida glabrata, superoxide dismutase (SOD) expression, critical for resistance to the superoxide-generating compound menadione, is independent CT99021 manufacturer of both CgSkn7 and CgYAP1 (Roetzer et al., 2011). The C. heterostrophus double mutant showed increased sensitivity to menadione (Fig. 1). Thus, the ‘wiring’ of the Skn7 and Yap1-dependent signaling pathways in the plant pathogen studied here is different from that in C. glabrata, but in both species SOD

will be an important enzyme activity to study further. On commercial hybrid maize cultivars Jubilee (Lev et al., 2005) and Royalty (this study), loss of ChAP1 did not compromise virulence in droplet inoculation assays. On the maize cultivar W64A, spray inoculation with Δchap1 resulted in about twofold decreased lesion size as compared with WT (Zhang et al., 2013). Necrotrophs like C. heterostrophus are thought to thrive in an oxidant-rich environment tuclazepam (see Heller & Tudzynski, 2011). The fungus thus must contend with ROS produced by both members of the host–pathogen pair. Skn7 senses not only oxidant stress, but also osmotic and cell wall stresses (Izumitsu et al., 2007; Oide et al., 2010; Fassler & West, 2011), and ChAP1 also appears to have redox-independent sensory functions (Shanmugam et al., 2010; Shalaby et al., 2012). In Candida glabrata, certain combinations of oxidative, nitrosative and osmotic stress were more potent than each alone (Kaloriti et al., 2012). On the plant, C.