Genomics and Biochemistry of Spruce Defense against Insects

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Conifers are the dominant trees of the Canadian forest landscape. They are also the most economically important trees for the forest industry. However, with climate change, conifer forest health is increasingly threatened by outbreaks of forest insect pests. Advanced knowledge of conifers' natural defenses against insects is essential for breeding programs to deliver trees with improved resistance. Conifers have evolved complex natural defense systems, which include combinations of chemical defenses and physical barriers against insects. Biosynthesis and accumulation of oleoresin is a major conifer defense against insects. Oleoresin consists of hundreds of different bioactive molecules, known as terpenes. Oleoresin composition is highly variable between different conifer species and within the same species. Two large classes of conifer genes and their enzymes, terpene synthases and cytochrome P450s, generate the enormous diversity and variability of oleoresin terpenes. Oleoresin terpenes are biosynthesized in specialized cell types that form the anatomical structures of resin ducts. Resin duct development and terpene biosynthesis occur as constitutive and insect-induced defenses. Resin ducts, terpenes, and other defenses provide strong protection for conifers against most insects. However, during outbreaks some highly destructive pests may overcome these defenses. The proposed project builds on the foundation of my long-term and internationally leading research program on (i) conifer genomics, (ii) conifer defense and (iii) terpene biosynthesis. The long-term goal of my program is to develop a genomics-informed, comprehensive understanding of complex conifer defense systems with applications in forest health. The project focuses on spruces, which are the most reforested conifer trees in Canada, and two of their major pests (weevils, budworms). Spruce breeding programs identified unique genotypes that are resistant or tolerant to these pests. However, much of the underlying defense mechanisms and their genomic underpinnings remain to be discovered. The three specific objectives are to (1) Comprehensively explain the chemical diversity and plasticity of terpene defenses; (2) Discover molecular mechanisms of induced terpene biosynthesis; and (3) Discover genomic and biochemical mechanisms that explain unique metabolic phenotypes associated with insect resistance. The research, collaborations and communications under these objectives provide exceptional graduate student training opportunities. The project will use our leading technology platforms and data resources in conifer genomics. It will address long-standing questions and new hypotheses on critical components of conifer defense systems. It will deliver advanced fundamental knowledge on conifer resistance and inform practical applications in collaborations with tree breeding programs.