1998; Ahlholm et al. 2000; Lehtonen et al. 2005; Saikkonen et al. 2004; Gundel et al. 2006, 2010, 2011; Sullivan and Faeth 2008; Cheplick and Faeth 2009; Hamilton et al. 2009 and 2010; Rodriquez et al. 2004 and 2009; Rudgers et al. 2009; Johnson Selleckchem CHIR 99021 et al. 2010; Saikkonen et al. 2010; Mouhamadou et al. 2011; Purahong and Hyde 2011; Tejesvi et al. 2011; Vesterlund et al. 2011). The benefit of endophytic fungi to a diverse group of host plants has commonly been observed in nutrient poor environments and when plants are under stress such as drought, flooding, plant competition, herbivory, and pathogen attacks

(Hesse et al. 2003; Rodriguez et al. 2004; Clarke et al. 2006; Schardl et al. 2004; Saikkonen et al. 2006; Morse et al. 2007; Hahn et al. 2008;

Saikkonen et al. 2010; Gundel et al. 2012; Torres et al. 2012). AZD8931 cost These fungi include root associated dark septate endophytes as well as obligate and facultative, asymptomatic endophytes residing within above-ground plant parts of the hosts throughout the fungal life cycle (systemic and vertically transmitted endophytes; e.g. Neotyphodium; Box 1). In addition, all plants host a diverse community of horizontally transmitted endophytic fungi which are often close relatives to pathogens (e.g. Trichoderma spp., Colletotrichum spp., Cladosporium spp., Phomopsis spp., Phyllosticta spp., and Fusarium spp. (Saikkonen 2007; Ghimire et al. 2011; González and Tello 2011; Rocha et al. 2011; Udayanga et al. 2011; Wikee et al. 2011). Tanaka et al. (2006 and 2008) demonstrated

reactive oxygen Dinaciclib cost species bursts originating from a mutualistic endophyte are required to inactivate plant defense responses against the fungus thereby maintaining the mutualism. Whether the suppression of plant defense is the result of fungal, plant, or symbiotum metabolism is poorly understood (Fig. 2). Because reactive oxygen species play a mechanistic role in programmed cell death, general stress responses and systemic signaling, they can have multifarious effects on the success of fungal infection or endophyte colonization and the plant responses, i.e. resistance, acceptance, or sanctioning. Moreover, antioxidants can serve to transmit stress signals through the oxidant-antioxidant interaction (CH Foyer, pers. comm.; Box 1). This may facilitate the chemical communication between a host and an PLEKHB2 avirulent pathogen or asymptomatic endophyte enabling the host to react quickly to pathogenesis and differentiate a pathogen from a mutualist (Fig. 2). A sophisticated mammalian immune recognition system, called the ‘innate immune system’ has evolved to distinguish invading microbes (Medzhitov and Janeway 1997). Future studies are needed to reveal if such a system exists in plants. Despite the nascent stages of research, there is evidence to indicate fungi both produce antioxidants in vitro and also alter the activity level of antioxidants in planta (Pang and Wang 2010; Harman 2011; Figs.