Contrasting Plant Defense Responses against Insect Vectors from Two Feeding Guilds

Plants mediate the interactions between insects and pathogens in numerous ways. The primary mechanism thought to underlie plant-mediated insect-pathogen interactions is the activation of defense-related signaling pathways. For instance, insect feeding predominantly activates a defense pathway mediated by the phytohormone, Jasmonic acid (JA), whereas, pathogens primarily activate defenses that are regulated by the phytohormone, Salicylic acid (SA). In addition, insect vectors that transmit plant pathogens may subject plants to simultaneous attack due to feeding and pathogen transmission. We investigated how plants tailor their defense against insect vectors from two feeding guilds (chewing and piercing-sucking). The study system included the soybean plant, a chewing insect, soybean thrips and a piercing-sucking insect, soybean aphid. Soybean thrips was recently shown to transmit Soybean vein necrosis virus and soybean aphid vectors several viruses such as Soybean mosaic virus. Gene expression analyses indicated that JA was activated against thrips whereas SA was induced in response to aphid and both viruses. Exogenous application of JA and SA confirmed gene expression results in that JA application reduced thrips population whereas SA application lowered aphid numbers and also reduced virus infection. In the short-term, results of this study will shed light on the ecological and molecular interactions of plant, insects and viruses, and in the long-term this research can be applied to ecologically-based management programs of the insect vectors and diseases.http://opus.ipfw.edu/stu_symp2014/1042/thumbnail.jp