Discovery Of A Putative Spruce Budworm Resistance Gene

A naturally-occurring resistance phenotype was discovered through a longitudinal study over the course of a spruce budworm outbreak. A white spruce plantation was monitored yearly and it was found that some trees were repeatedly defoliated while others were left practically untouched. The resistant trees produced two phenolic compounds, piceol and pungenol, that accumulate to relatively high concentrations in the foliage (Delvas et al. 2011). The peak of accumulation is closely timed with the most intensive feeding by the larvae. In contrast, the heavily defoliated non-resistant trees do not accumulate these compounds but instead accumulate their glycosylated forms, namely picein and pungenin. The biosynthesis and glycosylation of these compounds is not described, although they are assumed to derive from the phenylpropanoid pathway. A microarray profiling experiment compared foliage (young needles) from several resistant and several non-resistant trees, with three replicates per tree. A few hundred genes were differentially expressed between the two types of trees, but a sequence encoding a putative glycosyl hydrolase (gh1) stood out as being very strongly expressed in the resistant trees and close to background in the non-resistant trees. Molecular analysis of the RNA transcripts and genomic DNA sequences indicate that the differences in expression may be caused by a heritable variation. The potential role of the gh1 in tree-insect interactions will be discussed. Discovery of this gene may impact on integrated pest management strategies including tree breeding and the detection of susceptible trees established plantations or natural stands.

Delvas et al (2011) Entomol. Exper. Applic. 141:35-44