Dynamics of Membrane Potential Variation and Gene Expression Induced by <em>Spodoptera littoralis</em>, <em>Myzus persicae</em>, and <em>Pseudomonas syringae</em> in Arabidopsis

<div><h3>Background</h3><p>Biotic stress induced by various herbivores and pathogens invokes plant responses involving different defense mechanisms. However, we do not know whether different biotic stresses share a common response or which signaling pathways are involved in responses to different biotic stresses. We investigated the common and specific responses of <em>Arabidopsis thaliana</em> to three biotic stress agents: <em>Spodoptera littoralis</em>, <em>Myzus persicae</em>, and the pathogen <em>Pseudomonas syringae</em>.</p> <h3>Methodology/Principal Findings</h3><p>We used electrophysiology to determine the plasma membrane potential (V_m) and we performed a gene microarray transcriptome analysis on Arabidopsis upon either herbivory or bacterial infection. V_m depolarization was induced by insect attack; however, the response was much more rapid to <em>S. littoralis</em> (30 min −2 h) than to <em>M. persicae</em> (4–6 h). <em>M. persicae</em> differentially regulated almost 10-fold more genes than by <em>S. littoralis</em> with an opposite regulation. <em>M. persicae</em> modulated genes involved in flavonoid, fatty acid, hormone, drug transport and chitin metabolism. <em>S. littoralis</em> regulated responses to heat, transcription and ion transport. The latest Vm depolarization (16 h) was found for <em>P. syringae</em>. The pathogen regulated responses to salicylate, jasmonate and to microorganisms. Despite this late response, the number of genes differentially regulated by <em>P. syringae</em> was closer to those regulated by <em>S. littoralis</em> than by <em>M. persicae</em>.</p> <h3>Conclusions/Significance</h3><p>Arabidopsis plasma membranes respond with a V_m depolarization at times depending on the nature of biotic attack which allow setting a time point for comparative genome-wide analysis. A clear relationship between V_m depolarization and gene expression was found. At V_m depolarization timing, <em>M. persicae</em> regulates a wider array of Arabidopsis genes with a clear and distinct regulation than <em>S. littoralis</em>. An almost completely opposite regulation was observed between the aphid and the pathogen, with the former suppressing and the latter activating Arabidopsis defense responses.</p>