Location: Corn Host Plant Resistance ResearchTitle: Plants on constant alert: elevated levels of jasmonic acid and jasmonate-induced transcripts in caterpillar resistant maize Author
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2010
Publication Date: 2/11/2010
Citation: Shivaji, R., Camas, A., Ankala, A., Engelberth, J., Tumlinson, J.H., Williams, W.P., Wilkinson, J.R., Luthe, D.S. 2010. Plants on Constant Alert: Elevated Levels of Jasmonic Acid and Jasmonate-Induced Transcripts in Caterpillar Resistant Maize. Journal of Chemical Ecology. 36:179-191. Interpretive Summary: Corn germplasm lines with resistance to fall armyworm and southwestern corn borer and other Lepidoptera have been developed and released by USDA-ARS scientists at Mississippi State, MS. These lines have higher levels of jasmonic acid than lines that are susceptible to insect feeding. In a comparison of Mp708, a resistant line, and Tx601, a susceptible line, Mp708 had constitutively high levels of jasmonic acid and jasmonic synthesis was induced in Tx601 only in response to insect feeding conversely, salicylic acid levels were lower in both insect-infested and non-infested Mp708 plants than Tx601 plants. This suggests that jasmonic and salicylic acid have antagonistic effects on defensive responses to insects in these plants. Although molecular mechanisms regulating constitutive accumulation of jasmonic acid in Mp708 are not known, this germplasm line could be valuable in biochemical pathways involved in the response of corn to insect feeding.
Technical Abstract: Plant defense responses against insect herbivores frequently depend on the biosynthesis and action of jasmonic acid (JA) and its conjugates. To better understand JA signaling pathways in maize (Zea mays L.), we have examined two maize genotypes, Mp708 and Tx601. Mp708 is resistant to feeding by lepidopteran larvae and constitutively accumulates elevated levels of JA whereas the susceptible genotype Tx601 induces JA synthesis only in response to feeding. The constitutive expression of JA-related genes also is higher in Mp708 and Tx601 and larval feeding results in a large increase of OPDA accumulation in Mp708. In control and infested Mp708 plants salicylic acid (SA) levels are lower than those in Tx601 suggesting that SA and JA have antagonistic effects on insect defense responses in these plants. The resistant genotype also displays exceptionally high expression of a lipoxygenase (LOX) gene whose product, hydroperoxy-linolenic acid, can be further metabolized into volatile aldehydes and alcohols. In response to herbivory Mp708 generates comparatively higher amounts of hydrogen peroxide and increased senescence is observed at feeding sites. The mechanisms involved in the induction, perception and transduction of JA signals into functional responses is not well understood in maize, particularly, at the midwhorl stage of growth when plants are vulnerable to lepidopteran damage. Although the molecular mechanisms regulating the constitutive accumulation of JA in Mp708 are unknown, this genotype may be valuable in studying signaling pathways that maize uses to respond to insect herbivores.