From genotypes to phenotypes: expression levels of genes encompassing adaptive SNPs in black spruce

Julien Prunier, Guillaume Tessier, Jean Bousquet, John MacKay

Measuring transcript levels for adaptive genes revealed polymorphisms having cis -effect upon gene expression levels related to phenotype variation in a black spruce natural population. Trees growing in temperate and boreal regions must acclimate to changes in climatic factors such as low winter temperatures to survive to seasonal variations. Common garden studies have shown that genetic variation in quantitative traits helps species to survive and adapt to environmental changes and local conditions. Twenty-four genes carrying SNPs were previously associated with genetic adaptation in black spruce (Picea mariana [Mill.] BSP). The objectives of this study were to investigate the potential role of these genes in regulation of winter acclimation and adaptation by studying their patterns of expression as a function of the physiological stage during the annual growth cycle, tissue type, and their SNP genotypic class. Considerable variability in gene expression was observed between different vegetative tissues or organs, and between physiological stages. The genes were expressed predominantly in tissues that could be linked more directly to winter acclimation and adaptation. The expression levels of several of the genes were significantly related to variation in tree height growth or budset timing and expression level variation related to SNP genotypic classes was observed in four of the genes. An interaction between genotypic classes and physiological stages was also observed for some genes, indicating genotypes with different reaction norms in terms of gene expression.