A MODEL OF SILICON-INDUCED BASAL RESISTANCE IN TOMATO AGAINST RALSTONIA SOLANACEARUM BASED ON TRANSCRIPTOMIC AND BIOCHEMICAL ANALYSES. K. WydraLeibniz Universität Hannover, Institute of Plant Diseases and Plant Protection, Herrenhäuser Str. 2. 30149 Hannover, Germany. wydra@ipp.unihannover.de

Abstract: Application of silicon (Si) in form of Si dioxide and monosilicic acid induced resistance in tomato against bacterial wilt caused by Ralstonia solanacearum. Analyzing the gene expression of defense-related genes by quantitative real time PCR (qRT-PCR), up-regulation of JERF3, TSRF1, ACCO, FD-I, POD and AGP-1g in Si-amended, but not in untreated plants was observed after challenging with the pathogen. These genes play a role in ethylene (ET) and jasmonic acid (JA) signaling pathways and/or are involved in expression of basal resistance. Former immunohistochemical analysis of plant cell wall reactions to infection were partly confirmed by expression of AGP-1g, playing a role in defense related structural changes of the cell wall. Gene expression was generally highest at 72 hours post inoculation. At this time point gene expression analysed by the TOM2 microarray revealed sixteen genes significantly up- or down-regulated in plants treated with Si challenged with R. solanacearum compared to plants without Si application. The microarray results were validated by qRT-PCR, and the genes were annotated and functionally classified. At least twelve genes involved in defense, signal transduction, response to stresses, transcription, ubiquitinylation and metabolism were up-regulated. Highest upregulation of 11.0 log2 fold was found with the tify (ZIM)-protein JAZ1, involved in regulation of the JA-signaling pathway. A role of Si in priming the defense capacity of the plant involving reactive oxygen species (ROS), ET and JA signaling pathways and thereby alleviating biotic stress imposed by the pathogen is suggested and a hypothetical model of silicon-induced resistance (SiIR) presented.