FIGURE 1.

Selected species of root-associated microbes are known to elicit induced systemic resistance (ISR) by priming for enhanced expression of plant defense-associated genes which become active only after insect or pathogen attack. Depending on microbe species (indicated in brown or blue circles) or strain, ISR can be triggered via JA/ET- or SA-signaling pathways, in which each pathway activates different sets of defense-associated genes. It is hypothesized that application of multiple root-associated microbes that mediate ISR via different signaling pathways may activate higher diversity of defense-associated genes that can enhance plant defense against insects or pathogens. Crosstalk between multiple signaling pathways (JA/ET–SA) regulating ISR within the plant and on how it will affect the outcome of interactions is not known. Different shape of symbols in the leaves represent different defense- associated genes.