Conifers display a very large array of defenses
against insects and insect-associated fungal pathogens. These defenses include
a myriad of combinations of constitutive and induced, chemical and physical,
direct and indirect, as well as local and systemic defenses. Among some of the
most prominent defenses in conifers are terpenoid (e.g. oleoresin) and phenolic
secondary metabolites. Traumatic resinosis involves methyl jasmonate or
ethylene-inducible de novo differentiation of specialized anatomical structures
(traumatic resin ducts) for induced terpenoid accumulation in the developing
xylem. Similarly, phenolic defenses may involve the induction of specialized
phloem parenchyma (PP) cells. Insect induced volatile emissions are based on
passive release of resin terpenoids and on the active de novo formation and
emission of non-resin monoterpenes and sesquiterpenes.
We are investigating the defense and resistance
mechanism in weevil resistant and susceptible genotypes of Sitka spruce and in interior spruce. For
example, in our genomics-based biochemical characterization of insect-induced terpenoid
defenses, we are functionally characterizing a very large family of terpenoid
synthases (TPS) and analyze their expression in response to insect attack. Other
work is targeting cytochrome P450 genes and other insect-induced defense gene
families.
Our research on the large and rapidly evolving TPS
gene family and on terpenoid metabolite profiles has revealed molecular and
biochemical mechanisms that underlie plasticity and diversity of conifer chemical
defenses. The diversity of terpenoid and
other chemical defenses contributed at least in part, to the successful
evolution of long-lived conifer trees, which often survive for several hundred
years in the same location defeating many generations of faster evolving insect
pests and pathogens.
Large-scale genomics resources for species of
spruce as well as optimized proteomics and metabolite profiling tools have been
developed in our conifer genomics program and have been applied for a
comprehensive analysis of conifer chemical defense against insect attack. In
parallel, we are studying the possible counterattack mechanisms of insects
(e.g. bark beetles) and their associated fungal pathogens which may help these
organisms to overcome the defenses of conifers.
Among the goals we would
like to achieve is the identification of constitutive and insect-induced
defense mechanisms which will be pursued by:
- transcript-, proteome-, and
metabolite profiling;
- characterization of cell- or tissue-specific defense
mechanisms based on tissue micro-dissection;
- functional identification of
defense genes and gene families using in vivo and in vitro assay
systems;
- investigation of the size and diversification of defense gene
families in spruce;
- identification of regulatory systems for selected
defense genes and mechanisms.