Cis-Jasmone primes defense pathways in tomato via emission of volatile organic compounds and regulation of genes with consequences for Spodoptera exigua oviposition

Abstract

The role of cis-Jasmone (CJ) in priming plant defense against insect feeding is well documented in the literature. However, little is known about the role of CJ in mediating oviposition behavior of insects via changes in emission of volatile organic compounds (VOCs). Here, we hypothesized that foliar application of CJ will prime induction of plant defense in tomato via enhanced emission of VOCs with consequences for oviposition by Spodoptera exigua, an important pest of tomato. First, we quantified VOCs and the transcript levels of key genes that encode VOC biosynthesis in CJ-treated plants with S. exigua caterpillar infestation (CJI), untreated plants with S. exigua caterpillar infestation (UI), CJ-treated plants without S. exigua caterpillar infestation (CJ), and untreated plants without S. exigua caterpillar infestation (U). Next, oviposition preference of S. exigua was compared between CJI and UI, and between CJ and U. Gas chromatograph coupled-mass spectrometry (GC-MS) analyses showed that several key plant VOCs, including green leaf volatiles, monoterpenes, and a sesquiterpene, were emitted in significantly higher amounts in CJI compared to UI, CJ, or U. Consistent with the GC-MS results, the transcript levels of certain terpene synthase genes involved in the biosynthesis of many VOCs were higher in CJI plants. Consequently, S. exigua laid fewer numbers of eggs on CJI than UI. Moreover, in an in vitro oviposition choice test using filter paper, S. exigua laid significantly fewer eggs on filter papers containing VOCs from CJI compared to UI. These results indicate that CJ treatment followed by caterpillar infestation can prime tomato plant defense with potential ramifications for insect oviposition.