Plant Physiology Forum

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Plant Physiology Forum

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1. Plant Physiology Forum Co-ordinators: Phillip Joy & Kathy Pickle

2. Insect-Induced Conifer Defense. Miller, B., Madilao, L.L, Ralph, S., and Bohlman, J. 2005. Plant Physiol. 137: 369-382.

3. Forestry Problems Bark invading insects are major economic and ecological concerns Beetles and their vectored fungal pathogens are the most destructive agents of conifer forests worldwide. Pest management practices in agriculture do not apply to forestry. Conifers have evolved defense strategies towards these invaders overlapping mechanical and chemical defenses and the capacity to up-regulate additional defenses.

5. Chemical Defense Diverse group of terpenoids derived from isoprene C5H8 units different terpenoids have different multiples of units Mono-, di-, and, sesqui- Major components of oleresins Function as repellents or toxins to herbivores or pathogens

6. Resin Secretion formed in special resin canals Exuded in soft drops from wounds Resins seal the plant's wounds, kill insects and fungi, and allow the plant to eliminate excess metabolites.

8. The Experiment Purpose: To determine if stem-boring insects and methyl jasmonate (MeJA) treatments invoke similar defenses in conifers. Analyzed: Oleoresin mixtures Emissions of terpenoid volatiles Expression of terpenoid synthase (TPS) genes

9. Methyl-Jasmonate (MeJA) Among the most potent plant signaling molecules Damaged or infested plants produce higher levels of MeJA Defense mechanisms include: Interference with herbivore digestive system deterring insect feeding. Volatile organic molecules that serve as attractants for predators of the herbivores. act as a messenger to neighboring undamaged plants, prompting them to produce defensive chemicals Treatment with MeJA induced formation of resin ducts increased accumulation of oleoresin terpenoids Unclear how well MeJA treatment mimics the effects of insects in inducing defense.

10. Results Trepenoid accumulation in stems Both Weevil and MeJA induced traumatic resin duct formation Increase of Terpenoids after treatment with MeJA or Weevil attack

11. Results TPS Transcript Accumulation in Stems Both MeJA and Weevil induce mono-TPS Both MeJA and Weevil induce di-TPS Weevil induces Sesqui-TPS Spatial Patterns of Weevil defense Weevils on top: no increase of terpenoids in distal tissue Weevils on bottom: an increase of TPS in upper tissue

12. Results Emissions MeJA Max at 3d Diurnal Weevil Max at 6-12hr Not diurnal Active mechanisms, not passive release from ducts and blisters Larger variety of emissions where ID

13. Results What’s going on in the needles? Monotrepeniods, specifically (-)- linaloon (an alcohol) is formed and released from the needles No Ditrepeniods are found

14. Discussion Both Weevil and MeJA induce similar chemical defense Weevil defense is stronger and more complex They activated similar TPS genes, but Weevils induced more and with more strength So, can MeJA be used to ‘jump-start’ Weevil defense??

15. Discussion Both Weevil and MeJA induce Traumatic resin ducts to be formed Stronger for Weevils Due to the wounding factor? Due to continues feeding? Is MeJA releasing the passive/stored terpenoids? More likely activating their production What is the role of the stored terpenoids?

16. Discussion Weevil feeding causes some signal translocation, will MeJA? What other Octadecanoid pathway intermediates are involved? JA synthesis pathway What about other xylem regulators (forms TDs)? Ethylene?

17. Conclusion MeJA induces some of the same defenses as Weevil attack, therefore it may be able to activate Weevil defense prior to attack The role of TDs are still not truly understood Contain terpenoids, are formed as a defense mechanism, fills with resin Are the emissions inter-plant communication?

18. Questions & Comments

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