Working model of ZmLOX3 involvement in suppression of ISR Responses. In unperturbed maize roots, LOX3-derived oxylipins down-regulate defense-related genes and maintain levels of the defensive and developmental hormones, jasmonate (JA) and ethylene (ET) at healthy levels required for normal seed germination, plant growth, and normal life span (Gao et al., 2008). Upon colonization of roots, Trichoderma virens produces small molecules that possesses signaling activity and modulate gene expression in the roots to allow for mutualistic interactions with the host. One of such signal effecting expression of the host genes is a secreted proteinaceous elicitor, SM1 (Djonovic et al., 2007). One of the functions of SM1-mediated signaling is the down-regulation of expression of the host gene, ZmLOX3, which, in turn, results in de-repression of several defense and signaling host molecules including 9/13-LOX products (such as JA, traumatin, green leaf volatiles, or other oxylipins derived either from C18:3 or C18:2 polyunsaturated fatty acids) and ET. Some of these metabolites, their derivatives or their precursors are transported via xylem into aboveground organs where they signal changes in transcription of a number of defense-related genes including, upregulation of pathogenesis-related genes (e.g., PR5), phenylalanine ammonia lyase (PAL), several defense related LOXs such as LOX1, LOX2, LOX9, and other genes required for biosynthesis of JA, ROS, NO, and cell-wall fortification (e.g., lignin), phytoalexins, and other defense-related metabolites. In addition to up-regulation of defense genes, the host susceptibility genes that promote colonization of tissues by diverse pathogens are down-regulated. This includes LOX10 and LOX5 genes shown to promote disease (Christensen, 2009; Park, 2011). Collectively, these reprogramming in metabolome and transcriptome results in heightened defense status known as ISR in systemic tissues leading to increased resistance upon pathogen attack.