Priming of elm defence against herbivores

Principal Investigator: Prof. Dr. Monika Hilker

Plant responses to insect herbivory are known to be shaped by prior insect egg deposition. However, little knowledge is available in this respect for perennial K-selected plants. Project B1 aims to elucidate the impact of egg deposition by the multivoltine elm leaf beetle Xanthogaleruca luteola on the anti-herbivore defence of Ulmus minor.

In CRC-973-phase I, we showed that anti-herbivore defence of egg-deposited elms is more effective than of egg-free elms. We recorded increased mortality of larvae feeding on previously egg-deposited elm and fewer adult females resulting from surviving larvae. As fewer female beetles will limit the reproductive capacity of the herbivore´s population, elms likely benefit in the long run from taking the eggs as warning signals. Chemical analyses of numerous defence-related parameters of feeding-damaged leaves with and without prior egg deposition showed that especially phenolic compounds play a central role for the egg-mediated effects on the elm´s anti-herbivore defence. Currently we study transcriptomic and phytohormonal changes mediated by egg deposition in feeding-damaged and undamaged clonal elm trees propagated from a tissue culture maintained in our lab.

In CRC-973-phase II, our major questions are: (1) How is the egg-mediated increased anti-herbivore defence regulated on a spatial and temporal scale? These studies aim to elucidate how far the information about the priming signal (the egg deposition) is spread within a tree, how fast chemical and molecular changes occur in egg-deposited leaves damaged by feeding larvae and for how long they are maintained. (2) Do the known egg-induced changes in leaf odour act as priming stimulus, similarly to the well-known priming activity of feeding-induced leaf odour? (3) How is the priming effect of elm leaf beetle eggs affected by the eggs of co-occurring predators (here: coccinellids)? (4) How does feeding by predatory larval or adult coccinellids upon the elm leaf beetle eggs affect the elm´s priming of anti-herbivore defence? When coccinellids devour elm leaf beetle eggs, they usually do not feed 100% of the eggs, but leave the egg basis with a rest of the egg shell attached to the leaf surface. Do these left-overs of elm leaf beetle eggs destroyed by predators still affect the plant´s anti-herbivore defence against elm leaf beetle larvae? Or does the plant “relax” when the elm leaf beetle eggs are destroyed and does no longer keep a “warned” (primed) state?

We intend to study these questions on the mechanisms of priming of the elm´s anti-herbivore defence and on its ecological conditions by insect performance studies and analyses of transcript levels and metabolites of differently treated elm leaves.

References

• Beyaert, I., Koepke, D., Stiller, J., Hammerbacher, A., Yoneya, K., Schmidt, A., Gershenson, J. and Hilker, M. 2012. Can insect egg deposition „warn“ a plant of future feeding damage by herbivorous larvae? Proc. R. Soc. B 279:101-108.
• Austel, N., Eilers, E., Meiners, T. and Hilker, M. 2015. Elm leaves “warned” by insect egg deposition reduce survival of hatching larvae by a shift in their quantitative leaf metabolite pattern. Plant, Cell & Environ. doi 10.1111/pce.12619.
• Beyaert, I., Köpke, D., Stiller, J., Hammerbacher, A., Yoneya, K., Schmidt, A., Gershenzon, J. and Hilker, M. 2012. Can insect egg deposition „warn“ a plant of future feeding damage by herbivorous larvae? Proc. Roy. Soc. London, Ser. B 279: 101-108.
• Büchel, K., Fenning, T., Gershenzon, J., Hilker, M. and Meiners, T. 2015. Elm defence against herbivores and pathogens: Morphological, chemical and molecular regulation aspects. Phytochem. Rev. DOI 10.1007/s11101-015-9442-0.
• Büchel, K., Malskies, S., Mayer, M., Fenning, T.M., Gershenzon, J., Hilker, M. and Meiners, T. 2011. How plants give early herbivore alert: Volatile terpenoids attract parasitoids to egg-infested elms. Basic Appl. Ecol. 12: 403-412.
• Büchel, K., McDowell, E., Nelson, W., Descour, A., Gershenzon, J., Hilker, M., Soderlund, C., Gang, D.R., Fenning, T. and Meiners, T. 2012. An elm EST database for identifying leaf beetle egg-induced defense genes. BMC Genomics 13: 242.
• Geiselhardt, S., Yoneya, K., Blenn, B., Drechsler, N., Gershenzon, J., Kunze, R. and Hilker, M. 2013. Egg laying of cabbage white butterfly (Pieris brassicae) on Arabidopsis thaliana affects subsequent performance of the larvae. PLoS One 8: e59661.
• Hilker, M. and Fatouros, N.E. 2015. Plant responses to insect egg deposition. Annu. Rev. Entomol. 60: 493-515.
• Hilker, M. and Meiners, T. 2011. Plants and insect eggs: How do they affect each other? Phytochemistry 72: 1612-1623.
• Hilker, M., Schwachtje, J., Baier, M., Balazadeh, S., Bäurle, I., Geiselhardt, S., Hincha, D.K., Kunze, R., Mueller-Roeber, B., Rillig, M.C., Rolff, J., Romeis, T., Schmülling, T., Steppuhn, A., van Dongen, J., Withcomb, S.J., Wurst, S., Zuther, E. and Kopka, J. 2015. Priming and memory of stress responses in organisms lacking a nervous system. Biol. Rev. doi: 10.1111/brv.12215.