Tomato Plant Defenses against Helicoverpa zea

When insects feed on plants, the oral secretions inevitably come in contact with wounded plant tissue and play very important role in regulating plant defense. These studies used tomato (Solanum lycopersicum) and Helicoverpa zea (H.zea) as model system to study how oral secretions affect tomato defense. In my first set of experiments, I found that saliva collected from the spinnerets of H. zea had higher glucose oxidase (GOX) activity, which induced tomato defenses. Plants that were wounded mechanically and then treated with saliva or fungal GOX had higher levels of PIN2 gene expression in leaves and green fruits, while flowers and red fruit did not show comparable induction. GOX and saliva treatment also induce trichome number on newly growth leaf. Mechanically remove trichomes significantly increase insect damage and growth development.;Since trichomes contribute to plant resistance against herbivory by physical and chemical deterrents. To understand the role of different type trichome function in insect defense, the tomato trichome mutants were used to dissect trichome function in the defense. Study showed that hairless mutants had reduced number of twisted glandular trichomes (type I, IV, VI and VII) on leaf and stem, while woolly mutants had high density of non-glandular trichomes (type II, III and V) but only on the leaf. In both mutants, trichome densities were induced by methyl jasmonate (MeJA), but the types of trichomes present were not affected by MeJA treatment. Glandular trichomes contained high levels of monoterpenes and sesquiterpenes. High density of non-glandular trichome on leaves negatively influenced Leptinotarsa decemlineata (Colorado potato beetle, CPB) feeding behavior and growth, it stimulated H. zea growth. High glandular trichome density impaired H. zea growth, but had no effect on CPB. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that glandular trichomes highly express protein inhibitors (PIN2), polyphenol oxidase (PPOF) and hydroperoxide lyase (HPL) when compared to non-glandular trichomes. PIN2 in trichomes was highly induced by insect feeding in both mutant and wild type plants.;As defense signaling cascade is mediated by the synthesis, movement, and perception of jasmonate (JA) and its interaction with other plant hormones. In order to understand the interaction of ethylene and JA in regulating plant defense, the never ripe (Nr) mutant with a partial block of ethylene perception and the defenseless (def1) mutant with deficient in biosynthesis of JA were used to compare ethylene and JA interactions on tomato induced systemic defense. Proteinase inhibitor ( PIN2) was used as marker gene to compare the plant response. Exogenous application of MeJA increased plants resistance to Helicoverpa zea and induced tomato defense gene expression and glandular trichome density on systemic leaves. Exogenous application of ethephon, an elicitor that releases ethylene, increased insect growth and interfere the tomato wounding response. Hormone assay showed ethephon treatment increase salicylic acid (SA) on the systemic leaves. These results showed that JA plays the main important role on systemic induced defense. Ethylene negatively regulated tomato systemic defense. This study also found that insect herbivory or MeJA treatment of the maternal generation induces transgenerational tomato defense in the offspring by increasing glandular trichome density and by priming defense genes that are regulated by plant phytohormone signals.