Exploring the White Spruce Genome: Gene Content, Evolution and Expression

Conifer trees have genomes ranging from 18 to 30 Gigabases and life history traits that result in high levels of genetic diversity. The gene content of such large genomes has been the matter of some debate. The consequences of such large genome sizes on the evolution of gene families, gene structure and gene expression are also of interest to further our understanding of genome biology.

We developed a gene catalogue for the conifer Picea glauca from large-scale EST datasets and full length (FL) cDNA sequencing. This resource is comprised of 27,720 cDNA clusters, of which 85% are represented by FL insert cDNAs. We estimated that the P. glauca nuclear genome contains 32,520 transcribed genes. This estimate is in the same range as Arabidopsis and rice transcriptomes but is much lower than earlier conifer estimates. Functional and protein domain annotations highlighted the differential expansion of gene families related to stress responses when comparing conifers and angiosperms. The impact of gene family expansion was explored by RNA microarray profiling in from different tissues. The diversity of gene expression within large gene families related to osmotic stress was found to vary considerably. We also found that putative conifer specific genes are expressed in fewer tissues and at lower levels that sequences that are conserved among plant phyla, suggesting they may have more specialized or unique roles that remain to be uncovered. The presentation will also discuss structural features of conifer genes that may be a consequence their existence in such large genomes.