Silencing of G proteins uncovers diversified plant responses when challenged by three elicitors in Nicotiana benthamiana

Abstract

Signalling through heterotrimeric G protein composed of α-, β- and γ-subunits is essential in numerous physiological processes. Here we show that this prototypical G protein complex acts mechanistically by controlling elicitor sensitivity towards hypersensitive response (HR) and stomatal closure in Nicotiana benthamiana. Gα-, Gβ1-, and Gβ2-silenced plants were generated using virus-induced gene silencing. All silenced plants were treated with Xanthomonas oryzae harpin, Magnaporthe oryzae Nep1 and Phytophthora boehmeriae boehmerin, respectively. HR was dramatically impaired in Gα- and Gβ2-silenced plants treated with harpin, indicating that harpin-, rather than Nep1- or boehmerin-triggered HR, is Gα- and Gβ2-dependent. Moreover, all Gα-, Gβ1- and Gβ2-silenced plants significantly impaired elicitor-induced stomatal closure, elicitor-promoted nitric oxide (NO) production and active oxygen species accumulation in guard cells. To our knowledge, this is the first report of Gα and Gβ subunits involvement in stomatal closure in response to elicitors. Furthermore, silencing of Gα, Gβ1 and Gβ2 has an effect on the transcription of plant defence-related genes when challenged by three elicitors. In conclusion, silencing of G protein subunits results in many interesting plant cell responses, revealing that plant immunity systems employ both conserved and distinct G protein pathways to sense elicitors from distinct phytopathogens formed during plant-microbe evolution. In comparison to the activation of gene-for-gene-mediated plant cultivar-specific resistance, relatively little is known about the signaling pathways mediating non-cultivar-specific plant resistance. Our isolation of different pathogens-derived elicitors (bacterial harpin, fungal Nep1, and oomycete boehmerin) and characterization of its defense-inducing potential in N. benthamiana now provide suitable tools for such an approach. In our work, we determine the roles of N. benthamiana Gα and Gβ subunits (Gβ1 and Gβ2) in the elicitor signaling and to determine whether there was evidence that the heterotrimeric state of N. benthamiana G protein complex could play a regulatory role. Therefore, our work contributes to our understanding of the elicitor downstream signaling pathway in plant immunity, which may help determine similarities and differences in the molecular basis of distinct plant-microbe interactions. © 2011 Blackwell Publishing Ltd.