Comparative genome mapping among Picea glauca, P-mariana x P-rubens and P-abies, and correspondence with other Pinaceae

A composite linkage map was constructed from four individual maps for the conifer Picea glauca (Moench) Voss, from anonymous and gene-specific markfers (714 AFLPs, 38 SSRs, and 53 ESTPs). A total of 12 linkage groups were delineated with an average marker density of 2.7 cM. Macro-synteny and macro-colinearity comparisons with two other composite linkage maps developed for the species complex P. mariana (Mill.) B.S.P. x P. rubens Sarg., and for P. abies (L.) Karst. revealed an identical number of linkage groups and a remarkable conservation of the gene content and gene order of linkage groups over the million years since the split between these taxa. Identical gene order among taxa was observed for 10 of the 12 assembled composite linkage groups. The discovery of one breakdown in synteny between P. glauca and the other two taxa indicated the occurrence of an inter-chromosomal rearrangement involving an insertional translocation. Analysis of marker colinearity also revealed a putative segmental duplication. The combined information from these three Picea genomes validated and improved large-scale genome comparisons at the inter-generic level in the family Pinaceae by allowing for the identification of 11 homoeologous linkage groups between Picea and Pinus, and nine such groups between Picea and Pseudotsuga menziesii. Notably, the analysis of synteny among the three genera revealed a putative case of chromosomal fission and an inter-chromosomal rearrangement in the genome of P. menziesii. Both of these changes are inter-connected, indicating much instability in this part of the P. menziesii genome. Overall, the macro-structure of the Pinaceae genome was well conserved, which is notable given the Cretaceous origin of its main lineages.