AUTHOR=Creyaufmüller Friederike Carolin , Chassignet Isabelle , Delb Horst , Dounavi Aikaterini , Gailing Oliver , Leinemann Ludger , Kreuzwieser Jürgen , Teply-Szymanski Julia , Vornam Barbara 

TITLE=Terpene Synthase Genes in Quercus robur – Gene Characterization, Expression and Resulting Terpenes Due to Cockchafer Feeding

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 9 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01753

DOI=10.3389/fpls.2018.01753

ISSN=1664-462X

ABSTRACT=Global climate change increases the probability of drought stress in Central European forests, thereby weakening the vitality of forest trees. Biotic stress due to root herbivory caused by larvae of the forest cockchafer (Melolontha hippocastani) enhances the impact of drought on trees, particularly in oak forest rejuvenations. In Germany, geographically distant oak stands reveal huge differences in infestation strength by the forest cockchafer. While in Southwestern Germany this insect causes severe damage, oak forests in northern Germany are rarely infested in their lifetime. It is assumed that root-released volatile organic compounds (VOCs) are perceived by soil herbivores, thus guiding the larvae to the host roots. In this work, we exposed seedlings of two distant oak provenances to cockchafer larvae and studied their root-based VOC chemotypes, the terpene synthase properties and their attraction on larvae. We hypothesize, that (i) different oak provenances are genetically differentiated, (ii) specific terpene synthase genes are differently expressed in these provenances, (iii) the attraction for cockchafer larvae is different among oak provenances and is associated with the expression of terpene synthase genes and the terpenes released, and (iv) terpene synthase SNPs differentiate between oak provenances with high and low cockchafer population density.
Nuclear molecular markers indicated that the investigated oak populations were genetically highly variable although no clear genetic differentiation was found. The haplotypes observed at chloroplast DNA markers (maternally inherited, depict seed dispersal) showed typical patterns of migration from different refugial regions, with the populations in Southwestern Germany possessing haplotypes from different refugial regions. No clear association between genetic constitution of the different provenances and the abundance of cockchafer populations was observed. Five different oak terpene synthase genes were identified at the genomic level. Subsequent SNP analyses showed a differentiation between the collectives of up to 12.5 %. Gene expression analyses revealed geographic variation rather than a genotypic variation. Terpene synthase SNPs and the emitted terpenes differed between the provenances and reacted differently to larval feeding. The terpene bouquets released by the roots differed between oak populations and might be a reason for different presences of cockchafer.