Abstract
BackgroundAs a response to caterpillar feeding, poplar releases a complex mixture of volatiles which comprises several classes of compounds. Poplar volatiles have been reported to function as signals in plant-insect interactions and intra- and inter-plant communication. Although the volatile blend is dominated by mono- and sesquiterpenes, there is much to be learned about their formation in poplar.ResultsHere we report the terpene synthase (TPS) gene family of western balsam poplar (Populus trichocarpa) consisting of 38 members. Eleven TPS genes (PtTPS5-15) could be isolated from gypsy moth (Lymantria dispar)-damaged P. trichocarpa leaves and heterologous expression in Escherichia coli revealed TPS activity for ten of the encoded enzymes. Analysis of TPS transcript abundance in herbivore-damaged leaves and undamaged control leaves showed that seven of the genes, PtTPS6, PtTPS7, PtTPS9, PtTPS10, PtTPS12, PtTPS13 and PtTPS15, were significantly upregulated after herbivory. Gypsy moth-feeding on individual leaves of P. trichocarpa trees resulted in induced volatile emission from damaged leaves, but not from undamaged adjacent leaves. Moreover, the concentration of jasmonic acid and its isoleucine conjugates as well as PtTPS6 gene expression were exclusively increased in the damaged leaves, suggesting that no systemic induction occurred within the tree.ConclusionsOur data indicate that the formation of herbivore-induced volatile terpenes in P. trichocarpa is mainly regulated by transcript accumulation of multiple TPS genes and is likely mediated by jasmonates. The specific local emission of volatiles from herbivore-damaged leaves might help herbivore enemies to find their hosts or prey in the tree canopy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0270-y) contains supplementary material, which is available to authorized users.
Highlights
As a response to caterpillar feeding, poplar releases a complex mixture of volatiles which comprises several classes of compounds
The terpene synthase (TPS) gene family in P. trichocarpa To identify the members of the TPS gene family in P. trichocarpa, we conducted a BLAST analysis using the second improved version of the poplar genome (v3 assembly, http://www.phytozome.net/poplar)
The TPS-a subfamily with members and the TPS-b subfamily with members made up the majority of poplar TPSs, while only two members each fell into the TPS-g, TPS-c and the TPS-e subfamilies and only one TPS gene clustered within the TPS-f subfamily
Summary
As a response to caterpillar feeding, poplar releases a complex mixture of volatiles which comprises several classes of compounds. Poplar volatiles have been reported to function as signals in plant-insect interactions and intra- and inter-plant communication. The emission of VOCs from vegetative plant organs is often induced by biotic stresses like insect herbivory [3,4]. Such induced volatile blends can attract natural enemies of the herbivores, a reaction termed indirect defense [2]. Most plant genomes possess a midsize gene family encoding terpene synthases [12]. Based on their phylogenetic relationships, plant TPSs can be classified into seven different clades [12,13]. A new class of terpene synthases was found in S. moellendorffii which showed sequence similarity to microbial terpene synthases and were designated as microbial terpene synthase like (MTPSL) genes [14]
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