Maize defense elicitor, 12-oxo-phytodienoic acid, prolongs aphid salivation

Abstract

12-Oxo-phytodienoic acid (OPDA), an intermediate in the jasmonic acid (JA) biosynthesis pathway, regulates diverse signaling functions in plants, including enhanced resistance to insect pests. We previously demonstrated that OPDA promoted enhanced callose accumulation and heightened resistance to corn leaf aphid (CLA; <i>Rhopalosiphum maidis</i>), a phloem sap-sucking insect pest of maize (<i>Zea mays</i>). In this study, we used the electrical penetration graph (EPG) technique to monitor and quantify the different CLA feeding patterns on the maize JA-deficient <i>12-oxo-phytodienoic acid reductase</i> (<i>opr7opr8</i>) plants. CLA feeding behavior was unaffected on B73, <i>opr7opr8</i> control plants (- OPDA), and <i>opr7opr8</i> plants that were pretreated with OPDA (+ OPDA). However, exogenous application of OPDA on <i>opr7opr8</i> plants prolonged aphid salivation, a hallmark of aphids' ability to suppress the plant defense responses. Collectively, our results indicate that CLA utilizes its salivary secretions to suppress or unplug the OPDA-mediated sieve element occlusions in maize.