Genes, enzymes and chemicals of terpenoid diversity in the constitutive and induced defence of conifers against insects and pathogens*

Abstract

Contents Summary 657 Introduction 658 Identification and functional characterization of terpenoid pathway genes 658 Insect interactions with conifers 667 Conclusions and outlook 670 Acknowledgements 671 References 671 Summary Insects select their hosts, but trees cannot select which herbivores will feed upon them. Thus, as long‐lived stationary organisms, conifers must resist the onslaught of varying and multiple attackers over their lifetime. Arguably, the greatest threats to conifers are herbivorous insects and their associated pathogens. Insects such as bark beetles, stem‐ and wood‐boring insects, shoot‐feeding weevils, and foliage‐feeding budworms and sawflies are among the most devastating pests of conifer forests. Conifer trees produce a great diversity of compounds, such as an enormous array of terpenoids and phenolics, that may impart resistance to a variety of herbivores and microorganisms. Insects have evolved to specialize in resistance to these chemicals – choosing, feeding upon, and colonizing hosts they perceive to be best suited to reproduction. This review focuses on the plant–insect interactions mediated by conifer‐produced terpenoids. To understand the role of terpenoids in conifer–insect interactions, we must understand how conifers produce the wide diversity of terpenoids, as well as understand how these specific compounds affect insect behaviour and physiology. This review examines what chemicals are produced, the genes and proteins involved in their biosynthesis, how they work, and how they are regulated. It also examines how insects and their associated pathogens interact with, elicit, and are affected by conifer‐produced terpenoids.

Effect of Water Stress and Fungal Inoculation on Monoterpene Emission from an Historical and a New Pine Host of the Mountain Pine Beetle

“…This compound might function as an indicator of a weakened tree and could support the aggregation of beetles on susceptible hosts. MPB is able to distinguish between host and non-host volatiles, and may also use host volatiles to identify weak hosts and avoid the risks associated with trying to overcome tree defenses of a healthy host (Keeling and Bohlmann, 2006). Jack pine emits about three times more 3-carene than lodgepole pine, suggesting that it may be more prone to MPB attacks (Conn, 1981;Borden et al, 2008).…”

“…Trees that are mass attacked by the bark beetle plus associated fungi are defended with resin, a mixture of monoterpenes, sesquiterpenes, diterpenoid resin acids, and phenolic compounds characteristic of conifers (Keeling and Bohlmann, 2006) that act as physical and chemical defenses. Resin monoterpene composition differs between species, and the composition of individual trees in various pine species correlates with resistance to bark beetle attack (Sturgeon, 1979;Gollob, 1980).…”

Wood production, wood technology, and biotechnological impacts

“…It does not matter where a sink for carbon dioxide is established -its effects will reach within a short time the whole globe. Keeling et al 1996 andKeeling &Whorf 2005) …”

“…Isoprenoids are characteristic defence chemicals of conifers and are produced through the mevalonate (MEV) or methyl-erythritol-diphosphate (MEP) pathways (Keeling & Bohlmann 2006). They are highly variable in structure (>30,000 terpenes are known) and occur in trees as isoprene (C5), monoterpenes (C10), sesquiterpenes (C15) and diterpenes (C20) (Sharkey & Singsaas 1995, Phillips & Croteau 1999, Trapp & Croteau 2001.…”

A genomic approach to characterization of the Citrus terpene synthase gene family

“…Additionally, terpenes are also related to thermal protection, pollinator attraction, membrane stabilization, resistance against insects and microorgan-isms, plant-plant signaling, etc. (Steele et al, 1998;Trapp and Croteau, 2001;Copolovici et al, 2005;Baldwin et al, 2006;Keeling and Bohlmann, 2006).…”