Abstract
The mutualistic basidiomycete Piriformospora indica colonizes roots of mono- and dicotyledonous plants, and thereby improves plant health and yield. Given the capability of P. indica to colonize a broad range of hosts, it must be anticipated that the fungus has evolved efficient strategies to overcome plant immunity and to establish a proper environment for nutrient acquisition and reproduction. Global gene expression studies in barley identified various ethylene synthesis and signaling components that were differentially regulated in P. indica-colonized roots. Based on these findings we examined the impact of ethylene in the symbiotic association. The data presented here suggest that P. indica induces ethylene synthesis in barley and Arabidopsis roots during colonization. Moreover, impaired ethylene signaling resulted in reduced root colonization, Arabidopsis mutants exhibiting constitutive ethylene signaling, -synthesis or ethylene-related defense were hyper-susceptible to P. indica. Our data suggest that ethylene signaling is required for symbiotic root colonization by P. indica.
Highlights
Ethylene plays a prominent role in senescence and plant development [1,2]
Two-day-old barley seedlings were transferred to agar plates containing 100 mM of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), or to a jar containing a vial with 1 mM of the ethylene antagonist 1methylcyclopropene (MCP), which blocks ethylene signaling by interacting with ethylene receptors [28]
These data suggest that colonization of barley and Arabidopsis roots by P. indica is supported by ethylene signaling
Summary
Ethylene plays a prominent role in senescence and plant development [1,2]. In Arabidopsis thaliana, ethylene is perceived by five ER membrane-bound receptors (e.g. Ethylene Triple Response 1, ETR1). In the absence of ethylene, the receptors activate a Raf-like kinase (Constitutive Triple Response 1, CTR1), which negatively regulates the downstream ethylene response pathway [3]. Binding of ethylene inactivates the receptors, resulting in the deactivation of CTR1, which allows downstream effectors such as Ethylene Insensitive 2 (EIN2) to function as positive regulators of ethylene signaling [4,5] by activating transcription factors Ethylene Insensitive 3 (EIN3) and EIN3-like 1 (EIL1) [6]. The recognition of bacterial flagellin by the PRR Flagellin Sensing 2 (FLS2) results in the activation of an array of immune responses summarized as MAMP-triggered immunity (MTI), and includes the rapid production of reactive oxygen species (ROS) as well as ethylene [15]. Ethylene has a more complex role in the activation of early and late immune responses
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