Abstract
In plants, relationships between resistance to herbivorous insect pests and growth are typically controlled by complex interactions between genetically correlated traits. These relationships often result in tradeoffs in phenotypic expression. In this study we used genetical genomics to elucidate genetic relationships between tree growth and resistance to white pine terminal weevil (Pissodes strobi Peck.) in a pedigree population of interior spruce (Picea glauca, P. engelmannii and their hybrids) that was growing at Vernon, B.C. and segregating for weevil resistance. Genetical genomics uses genetic perturbations caused by allelic segregation in pedigrees to co-locate quantitative trait loci (QTLs) for gene expression and quantitative traits. Bark tissue of apical leaders from 188 trees was assayed for gene expression using a 21.8K spruce EST-spotted microarray; the same individuals were genotyped for 384 SNP markers for the genetic map. Many of the expression QTLs (eQTL) co-localized with resistance trait QTLs. For a composite resistance phenotype of six attack and oviposition traits, 149 positional candidate genes were identified. Resistance and growth QTLs also overlapped with eQTL hotspots along the genome suggesting that: 1) genetic pleiotropy of resistance and growth traits in interior spruce was substantial, and 2) master regulatory genes were important for weevil resistance in spruce. These results will enable future work on functional genetic studies of insect resistance in spruce, and provide valuable information about candidate genes for genetic improvement of spruce.
Highlights
Plants are sessile organisms that have evolved many resistance mechanisms to defend against insect pests
We present results on the use of genetical genomics to investigate a question of fundamental importance in plant genomics: How do genes underlying a pathway to pest resistance concertedly function? We investigated growth and insect resistance as a trait pair that defines the life history of interior spruce, a commercially valuable and ecologically important coniferous tree species
Correlations between Phenotypic Estimates The phenotypic response data consisted of tree height measurements and weevil attack and oviposition counts
Summary
Plants are sessile organisms that have evolved many resistance mechanisms to defend against insect pests. A ‘‘cost-benefit’’ paradigm for resistance has emerged to enhance our understanding of these interactions [3,4,5,6,7]. This paradigm suggests that tradeoffs in the cost-benefit paradigm may be due to correlated selection (favored trait combinations) and spatio-temporal heterogeneity of the environment [8]. It has been hypothesized that both constitutive and induced resistance are influenced by selection on traits that alter plant growth rates [12]. Alfaro [13] suggested that in response to wounding, some resistant trees failed to produce the traumatic response and some susceptible trees responded with an unexpectedly intensified response
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