Impact of Seasonal and Temperature-Dependent Variation in Root Defense Metabolites on Herbivore Preference in Taraxacum officinale

Wei Huang,Zoe Bont,Christelle A M Robert,Matthias Erb,Maxime R Hervé

doi:10.1007/s10886-019-01126-9

Abstract

Plants experience seasonal fluctuations in abiotic and biotic factors such as herbivore attack rates. If and how root defense expression co-varies with seasonal fluctuations in abiotic factors and root herbivore attack rates is not well understood. Here, we evaluated seasonal changes in defensive root latex chemistry of Taraxacum officinale plants in the field and correlated the changes with seasonal fluctuations in abiotic factors and damage potential by Melolontha melolontha, a major natural enemy of T. officinale. We then explored the causality and consequences of these relationships under controlled conditions. The concentration of the defensive sesquiterpene lactone taraxinic acid β-D glucopyranosyl ester (TA-G) varied substantially over the year and was most strongly correlated to mean monthly temperature. Both temperature and TA-G levels were correlated with annual fluctuations in potential M. melolontha damage. Under controlled conditions, plants grown under high temperature produced more TA-G and were less attractive for M. melolontha. However, temperature-dependent M. melolontha feeding preferences were not significantly altered in TA-G deficient transgenic lines. Our results suggest that fluctuations in temperature leads to variation in the production of a root defensive metabolites that co-varies with expected attack of a major root herbivore. Temperature-dependent herbivore preference, however, is likely to be modulated by other phenotypic alterations.

Highlights

Over the course of the year, plants are exposed to substantial environmental variation, including diurnal and seasonalWei Huang and Zoe Bont contributed to this work.Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, SwitzerlandCAS Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, Hubei, ChinaInra, Agrocampus Ouest, IGEPP – UMR-A 1349, University of Rennes, F-35000 Rennes, France fluctuations in temperature, precipitation, photoperiod, pest and pathogen pressure (McClung 2006; Poelman et al 2008; Sanchez et al 2011)
Given that belowground herbivores are ubiquitous in natural systems, and that many of them spend several years in the soil feeding on plants as immatures before emerging as adults, understanding how root defenses vary across seasons and if this variation is associated with increased resistance and the probability of attack is an open question in the field of below ground plant-herbivore interactions
To understand if and how seasonal variation influences plant defense metabolites in the roots, if this fluctuation is associated with expected herbivore attack rates, and to what extent this fluctuation can explain herbivore preferences, we studied these processes in the common dandelion (Taraxacum officinale, Asteraceae)

Summary

Introduction

Over the course of the year, plants are exposed to substantial environmental variation, including diurnal and seasonal. Given that belowground herbivores are ubiquitous in natural systems, and that many of them spend several years in the soil feeding on plants as immatures before emerging as adults (van Dam 2009), understanding how root defenses vary across seasons and if this variation is associated with increased resistance and the probability of attack is an open question in the field of below ground plant-herbivore interactions. By combining field and growth chamber experiments, our study provides evidence that fluctuations in abiotic factors such as temperature lead to co-variation in the production of defensive metabolites and expected root herbivore attack, and shows that other temperature-dependent factors modulate the attractiveness of T. officinale plants to M. melolontha We asked the following questions: 1) Do root latex secondary metabolites show seasonal variations in T. officinale? 2) If so, can these changes be explained by fluctuating abiotic conditions such as humidity and temperature? 3) Are the changes synchronized with the probability of M. melolontha attack? 4) Do these changes in defense chemistry explain changes in plant attractiveness to M. melolontha? By combining field and growth chamber experiments, our study provides evidence that fluctuations in abiotic factors such as temperature lead to co-variation in the production of defensive metabolites and expected root herbivore attack, and shows that other temperature-dependent factors modulate the attractiveness of T. officinale plants to M. melolontha

Materials and Methods

Findings

Discussion