Identification and Regulation of TPS04/GES, anArabidopsisGeranyllinalool Synthase Catalyzing the First Step in the Formation of the Insect-Induced Volatile C16-Homoterpene TMTT

Abstract

Volatile secondary metabolites emitted by plants contribute to plant-plant, plant-fungus, and plant-insect interactions. The C 16 -homoterpene TMTT (for 4,8,12-trimethyltrideca-1,3,7,11-tetraene) is emitted after herbivore attack by a wide variety of plant species, including Arabidopsis thaliana, and is assumed to play a role in attracting predators or parasitoids of herbivores. TMTT has been suggested to be formed as a degradation product of the diterpene alcohol (E,E)-geranyllinalool. Here, we report the identification of Terpene Synthase 04 (TPS04; At1g61120) as a geranyllinalool synthase (GES). Recombinant TPS04/GES protein expressed in Escherichia coli catalyzes the formation of (E,E)-geranyllinalool from the substrate geranylgeranyl diphosphate. Transgenic Arabidopsis lines carrying T-DNA insertions in the TPS04 locus are deficient in (E,E)-geranyllinalool and TMTT synthesis, a phenotype that can be complemented by expressing the GES gene under the control of a heterologous promoter. GES transcription is upregulated under conditions that induce (E,E)-geranyllinalool and TMTT synthesis, including infestation of plants with larvae of the moth Plutella xylostella and treatment with the fungal peptide alamethicin or the octadecanoid mimic coronalon. Induction requires jasmonic acid but is independent from salicylic acid or ethylene. This study paves the ground to address the contribution of TMTT in ecological interactions and to elucidate the signaling network that regulates TMTT synthesis.

Variation of Herbivore-Induced Volatile Terpenes among Arabidopsis Ecotypes Depends on Allelic Differences and Subcellular Targeting of Two Terpene Synthases, TPS02 and TPS03

“…As previously demonstrated in accession Col-0, coronalon induces the emission of MeSA, (E,E)-a-farnesene, the homoterpene TMTT, and its precursor geranyllinalool, a response similar to that observed upon feeding damage by larvae of P. xylostella (Herde et al, 2008). By comparing emissions of volatile terpenes from leaves of intact plants treated with coronalon for 22 to 30 h, we found that 20 accessions released the monoterpene (E)-b-ocimene as the predominant volatile (approximately 75%-95% of the total amount of volatiles) at rates differing 80-fold between lowest and highest emitters (Table I).…”

“…4C). Moreover, no changes were observed for the induced transcription of the TPS02 pseudogene and the (Herde et al, 2008), these results strongly suggested that the TPS03 gene is responsible for the induced formation of (E,E)-a-farnesene in the Col-0 accession.…”

“…Previous feeding experiments with the specialist P. xylostella on Col-0 had shown that insect feeding induces a volatile response similar to that observed with coronalon (Herde et al, 2008). In this study, when P. xylostella larvae were applied to rosette leaves of accession Ws, a high-(E)-b-ocimene emitter, emission of (E)-b-ocimene, TMTT, and MeSA was induced upon 21 to 30 h of feeding (Supplemental Fig.…”

“…S1), with a compound ratio similar to that obtained upon coronalon treatment. Emission rates were substantially lower for all compounds [30-fold lower for (E)-b-ocimene] than after application of coronalon but in the range of those observed for Col-0 upon P. xylostella damage (Herde et al, 2008; Supplemental Fig. S1).…”

“…Here, we turn our attention to vegetative volatiles. Leaves of the Arabidopsis (Arabidopsis thaliana) accession Columbia (Col-0) release a simple threecompound blend consisting of the benzenoid compound methyl salicylate (MeSA), the C 16 -homoterpene 4,8,3,7,, and the sesquiterpene (E,E)-a-farnesene in response to treatment with the fungal peptide elicitor alamethicin and feeding by the crucifer specialist insects Pieris rapae and Plutella xylostella (Van Poecke et al, 2001;Herde et al, 2008). The induced volatile mixture is assumed to serve as an indirect defense signal by attracting parasitoids of P. rapae larvae.…”