Herbivore-induced defence response in the brown seaweed Fucus vesiculosus (Phaeophyceae): temporal pattern and gene expression

Abstract

This study aimed to reveal the dynamics of inducible anti-herbivory traits in the brown seaweed Fucus vesiculosus, in response to grazing by the isopod Idotea baltica. As the molecular basis of defence induction in seaweeds is poorly understood, a transcriptomic approach was used to gain insight into cellular processes underlying defence induction and thus promote the mechanistic understanding of anti-herbivory responses in seaweeds. In a 27 day feeding-assayed induction experiment, temporal patterns of the induced anti-herbivory resistance of F. vesiculosus were assessed under laboratory conditions. Feeding assays were performed at three day intervals, using fresh and reconstituted food. Microarray hybridizations investigating the expression of genes 3 days before, as well as at the same time as, feeding assays revealed a decreased palatability of previously grazed F. vesiculosus pieces compared with non-grazed control pieces. Despite permanent exposure to grazers, F. vesiculosus palatability varied over time. Non-grazed F. vesiculosus pieces were significantly preferred to grazed pieces after 18 and again after 27 days of previous grazing, while their relative palatability for isopods was comparable at all other times during the experiment. Relative to controls, 562/402 genes were ≥ 1.5-fold up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when induction of defences was detected in feeding assays. Massive reprogramming of the regulatory expression orchestra (translation, transcription) as well as up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defence and stress response was found. At the same time, down-regulation of photosynthesis was observed in grazed seaweed pieces. This study suggests a high level of temporal variability in induced anti-herbivory traits of F. vesiculosus and reveals increased expression of genes with putative defensive functions in conjunction with the reallocation of resources from primary to secondary metabolism.

Key words:

• Feeding preference
• gene expression
• grazing
• Idotea baltica
• microarray
• phenotypic plasticity
• seaweed-herbivore interaction

Acknowledgements

Financial support was provided by the PACES research program of the Alfred-Wegener-Institut (AWI) Helmholtz-Zentrum für Polar- und Meeresforschung. Microarray development and protocol adjustments for Fucus vesiculosus were supported by a grant of The Future Ocean Cluster of Excellence (Project ‘Model Macroalga’, CP0746-6) and a Marie Curie International Reintegration Grant of the EU to I.K. (Call: FP7-PEOPLE-2007-4-3-IRG; Project ‘IDA’, 208801). C.R.F. was financially supported by the Rosa Luxemburg Foundation. We thank Lisa Güntner for lab assistance and Shauna Murray for the language check of this manuscript.

Supplementary information

The following supplemental material is available for this article, accessible via the Supplementary Content tab on the article’s online page at http://dx.doi.org/10.1080/09670262.2014.946452.

Table S1. Results of the 2-factorial RM-ANOVA for the induction and reduction phase, comparing feeding rates affected by treatment (control/grazed) and time. Consumption was assessed in two-choice feeding assays using either fresh or reconstituted Fucus vesiculosus (n = 10).

Table S2. Complete list of Fucus vesiculosus genes that were differentially regulated between seaweed pieces that were previously grazed by I. baltica for 15 and 18 days, and non-grazed control pieces.

Table S3. Complete annotation list of the F. vesiculosus cDNA library.