Ethylene Signaling Regulates Accumulation of the FLS2 Receptor and Is Required for the Oxidative Burst Contributing to Plant Immunity

Abstract

Reactive oxygen species (ROS) are potent signal molecules rapidly generated in response to stress. Detection of pathogenassociated molecular patterns induces a transient apoplastic ROS through the function of the NADPH respiratory burst oxidase homologs D (RbohD). However, little is known about the regulation of pathogen-associated molecular pattern-elicited ROS or its role in plant immunity. We investigated ROS production triggered by bacterial flagellin (flg22) in Arabidopsis (Arabidopsis thaliana). The oxidative burst was diminished in ethylene-insensitive mutants. Flagellin Sensitive2 (FLS2) accumulation was reduced in etr1 and ein2, indicating a requirement of ethylene signaling for FLS2 expression. Multiplication of virulent bacteria was enhanced in Arabidopsis lines displaying altered ROS production at early but not late stages of infection, suggesting an impairment of preinvasive immunity. Stomatal closure, a mechanism used to reduce bacterial entry into plant tissues, was abolished in etr1, ein2, and rbohD mutants. These results point to the importance of flg22-triggered ROS at an early stage of the plant immune response.

Arabidopsis MPK3 and MPK6 Play Different Roles in Basal and Oligogalacturonide- or Flagellin-Induced Resistance against Botrytis cinerea

“…FRK1 and RetOx expression is altered, although to a lesser extent, also in mpk6-2 plants, but not in the mpk3-1 mutant, supporting our observation that MPK6 plays a predominant role in the activation of some defense responses upon elicitor treatment. Recent evidence indicates that the early oxidative burst induced by flg22 or elf8 is not impaired, or it is even slightly enhanced, in single mpk3 or mpk6 mutants (Mersmann et al, 2010;Ranf et al, 2011). These data suggest that either MPK3 and MPK6 have a fully redundant role in this elicitortriggered response or, conversely, that they are not required at all for this response; the latter hypothesis is supported by the wild-type-like oxidative burst observed in AP2C1-overexpressing plants treated with flg22 (this work).…”

“…Analysis of mapk single mutants suggests either a minor role or functional redundancy of MPK3 and MPK6 in the early oxidative burst induced by elicitors (Mersmann et al, 2010;Ranf et al, 2011). For this reason, this response was here analyzed in the AP2C1-overexpressing lines, which are affected in phosphorylation of both MAPKs.…”

Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction

“…Ethylene signaling directly controls FLS2 expression by inducing the activation of the EIN3/EIL family of transcription factors, which directly bind the FLS2 promoter (68). This binding leads to an increase in FLS2 protein accumulation (68,69). Mutants deficient in ethylene signaling pathways, such as ein2, have reduced FLS2 transcript levels with or without flg22 treatment (68), likely contributing to the susceptibility of ein2 mutants to weakened plant pathogens such as Pto DC3000 ΔavrPto/ΔavrPtoB (69).…”

“…As a control, we used an ethylene-insensitive protein 2 (ein2)-null mutant (67). Ethylene-insensitive mutants allow enhanced growth of weak pathogens and are defective in flg22-mediated priming of the immune system (68,69). In planta bacterial growth analyses show that Yang cycle mutants are more susceptible to Pto DC3000D28E, similar to ein2 (Fig.…”

Reactive oxygen species and plant resistance to fungal pathogens

“…They consist in non-fluorescent molecules that become fluorescent when oxidised by ROS, and the emitted fluorescence can be observed by fluorimetry and/or by fluorescent microscopy, an advantage of such probes (Benikhlef et al, 2013;Bulgakov et al, 2012;Fester and Hause, 2005;Guo et al, 2010;Kolla et al, 2007;L'Haridon et al, 2011;Li et al, 2007;Liu et al, 2010;Ma et al, 2013;Peleg-Grossman et al, 2012;Plancot et al, 2013;Tada et al, 2004;Wen et al, 2008;Ye et al, 2013). Luminol or luminol analogues are sensitive chemiluminescent probes used to quantify a relative intensity of ROS by counting the emitted light with a luminometer, CDD camera or a scintillation counter (Dubreuil-Maurizi et al, 2010;Flury et al, 2013;Kunz et al, 2006;L'Haridon et al, 2011;Mersmann et al, 2010). Finally, it is possible to determine the redox potential of the glutathione pool in a high spatial and temporal resolution using various redox-sensitive green fluorescent proteins (for example roGFP) encoded in the test plant.…”