Two enzymes responsible for the formation of herbivore-induced volatiles of maize, the methyltransferase AAMT1 and the terpene synthase TPS23, are regulated by a similar signal transduction pathway

Herbivore-induced volatiles play an important role in the indirect defense of plants. After herbivore damage, volatiles are released from the plant and can attract herbivore enemies that protect the plant from additional damage. The herbivore-induced volatile blend is complex and usually consists of mono- and sesquiterpenes, aromatic compounds, and indole. Although these classes of compounds are generally produced at different times after herbivore damage, the release of the terpene (E)-β-caryophyllene and the aromatic ester methyl anthranilate appear to be tightly coordinated. We have studied the herbivore induction patterns of two terpene synthases from Zea mays L. (Poaceae), TPS23 and TPS10, as well as S-adenosyl-L-methionine:anthranilic acid carboxyl methyltransferases (AAMT1), which are critical for the production of terpenes and anthranilate compounds, respectively. The transcript levels of tps23 and aamt1 displayed the same kinetics after damage by the larvae of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), and showed the same organ-specific and haplotype-specific expression patterns. Despite its close functional relation to TPS23, the terpene synthase TPS10 is not expressed in roots and does not display the haplotype-specific expression pattern. The results indicate that the same JA-mediated signaling cascade maycontrol the production of both the terpene (E)-β-caryophyllene and aromatic ester methyl anthranilate.

Metabolomics in plant-herbivore interactions: challenges and applications

Metabolomics as the study of the entire set of metabolites of a given organism is an important frontier in life sciences. As a tool that captures the ‘front end’ of cellular machineries, metabolomics is particularly suited to investigate biotic interactions, including for instance the interplay between plants and insects. In this review, we discuss the opportunities and challenges of metabolomics to study plant–herbivore interactions. We first present a brief overview of the typical analytical workflows used in metabolomics and their associated issues, in particular those related to metabolome coverage and compound identification. Second, recent advances in the field of plant–herbivore relationships that are promoted by non-targeted approaches are reviewed, with examples ranging from classical herbivore resistance patterns to plant-mediated interactions across different spatial scales and volatile-mediated tritrophic interactions. Through general considerations and the discussion of a few selected case studies, our review highlights the potential and challenges of metabolomics as a research approach to understand biological interfaces.

Belowground herbivore tolerance involves delayed overcompensatory root regrowth in maize

Plants can tolerate leaf-herbivore attack through metabolic reconfigurations that allow for the rapid regrowth of lost leaves. Several studies indicate that root-attacked plants can re-allocate resources to the aboveground parts. However, the connection between tolerance and root regrowth remains poorly understood. We investigated the timing and extent of root regrowth of tolerant and susceptible lines of maize, Zea mays L. (Poaceae), attacked by the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), in the laboratory and the field. Infested tolerant maize plants produced more root biomass and even overcompensated for the lost roots, whereas this effect was absent in susceptible lines. Furthermore, the tolerant plants slowed growth of new roots in the greenhouse and in the field 4–8 days after infestation, whereas susceptible plants slowed growth of new roots only in the field and only after 12 days of infestation. The quick response of tolerant lines may have enabled them to escape root attack by starving the herbivores and by saving resources for regrowth after the attack had ceased. We conclude that both timing and the extent of regrowth may determine plant tolerance to root herbivory.