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Plant Volatiles – Chemical Defense Mechanisms

Plant Volatiles – Chemical Defense Mechanisms . Symbiotic, antibiotic, and defense relationships. Acacias – sugar composition adjusted to desired ant species. Heil et al. (2005) Postsecretory hydrolysis of nectar sucrose and

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Plant Volatiles – Chemical Defense Mechanisms

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  1. Plant Volatiles – Chemical Defense Mechanisms Symbiotic, antibiotic, and defense relationships Acacias – sugar composition adjusted to desired ant species Heil et al. (2005) Postsecretory hydrolysis of nectar sucrose and specialization in ant/plant mutualism. Science 308 (5721) Plants provide sugars for which ants have no catabolic enzyme.

  2. predator’s Plant predator predator “Tri-trophic” Interactions Plant - Herbivore - parasitic Insect

  3. “Tri-trophic” Interactions forced regurgitating feeding damage maize, cotton, etc. e.g. Spodoptera littoralis parasitic wasps Schnee et al. (2006) The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores. PNAS 103, 1129

  4. JA biosynthesis – abbreviated From plant signaling to insect response via VOC – volatile organic compounds Farmer & Ryan (early 90s) – volatile signals from plant to plant Jasmonates Terpenes

  5. Turlings TCJ, Loughrin JH, McCall PJ, Rose USR, Lewis WJ, Tumlinson JH (1992) How caterpillar-damaged plants protect themselves by attracting parasitic wasps. PNAS 92, 4169. Plants respond to caterpillar feeding Healthy, undamaged corn seedlings 1 C6 6 hours after start of caterpillar feeding 5 C10 Some peak IDs (LC-MS): 1,2,3 – 3-hexenal; 2-hexenal; 3-hexenol 5- linalool; 9 – β-farnesene; 10 - nerolidol 10 C15 9 C15 IS1,2 – internal standards

  6. Feeding on cotton jasmone Change in composition over time of attack. Signaling compounds (or degradation products) at low levels. pinene 1st day 3rd day indole linalool farnesene

  7. Emitted compounds by cotton Start - 2 p.m. 5 caterpillars on 6w-old cotton A – LOX products from cotton B – constitutive cotton volatiles C – induced compounds in cotton

  8. LOX-products from corn Induced complex compounds Emissions by infected corn over time Leaves scratched, then added caterpillar regurgitate Recognition – timing, composition and nature of compounds

  9. Based on Isoprene & Isoprenoid metabolism Signals in caterpillar “spit” induce plant biodefense WMD by recruiting allied forces acetoacetyl-CoA + acetyl-CoA > HMG-CoA > mevalonate >>>> isopentenyl-PP C4 + C2 > C6 > C5 + CO2

  10. Isoprene Isopentenyl-PP Dimethylallyl-PP Geranyl-PP C5 C5

  11. C15 – farnesyl-PP Cyclic sesq. (cadinene) C20 - Geranyl-geranyl-PP Sesquiterpene type – phytol (retinol, retinal) 6β-acetoxy-24-methyl- 12, 24-dioxoscalaran-25-al (pacific sponge) C25 – Sesterterpines > abundant, non-volatile C30 - Triterpenes > steroid source structure, abundant, non-volatile C40 - Carotenes > carotenoid source structure, abundant, non-volatile

  12. Induction of sesquiterpene synthases maize Wasps fly straight to damaged leaf from downwind, not to a wounded leaf, but to wounded leaves treated with regurgitated midgut sap of insect.

  13. Gene to Product farnesene bergamotene sesquiphellandrene maize

  14. What happens when the gene is expressed in Arabidopsis ? A single transgene/ protein generates the entire spectrum! … but will the wasps know?

  15. Wt and transformed Arabidopsis – wasps in central compartment • naïve wasps • trained on Arabidopsis • trained on maize wt tr Side result – wasps must learn by trial & error, i.e., there are other cues; signals that connect wasp & caterpillar P < 0.01

  16. One could use the contraption for other experiments Western Corn rootworm Diobrotica v. virgifera Metabolomics to the Rescue! A major problem in US agriculture – is there a natural biodefense strategy (i.e., no chemicals)?

  17. One could use the contraption for other experiments Maize Western Corn rootworm Nematode Rasmann et al. (2005) Nature 434, 731. Trimorphic interaction involving a entomopathogenic nematode

  18. Experiments similar to the wasp predation experiment • Identification of attractant • Why is US maize not protected • Does it work in the field • Isoprenoids in the soil?

  19. Sesquiterpene hydrocarbons in maize A – leaf inducible, B – ubiquitous; C – root specific

  20. Terpene synthases in maize • Heterologous expression • GC-MS with isotopic tracers • GC-MS of different lines • Mutational analysis Sesquiterpene spectrum as affected by mutational analysis of the gene

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