High synteny and colinearity among Eucalyptus genomes revealed by high-density comparative genetic mapping

Understanding genome differentiation is important to compare and transfer genomic information between taxa, such as from model to non-model organisms. Comparative genetic mapping can be used to assess genome differentiation by identifying similarities and differences in chromosome organization. Following release of the assembled Eucalyptus grandis genome sequence (January 2011; http://www.phytozome.net/), a better understanding of genome differentiation between E. grandis and other commercially important species belonging to the subgenus Symphyomyrtus is required. In this study, comparative genetic mapping analyses were conducted between E. grandis, Eucalyptus urophylla, and Eucalyptus globulus using high-density linkage maps constructed from Diversity Array Technology and microsatellite molecular markers. There were 236-393 common markers between maps, providing the highest resolution yet achieved for comparative mapping in Eucalyptus. In two intra-section comparisons (section Maidenaria-E. globulus and section Latoangulatae-E. grandis vs. E. urophylla), similar to 1% of common markers were non-syntenic and within chromosomes 4.7-6.8% of markers were non-colinear. Consistent with increasing taxonomic distance, lower synteny (6.6% non-syntenic markers) was observed in an inter-section comparison between E. globulus and E. grandis x E. urophylla consensus linkage maps. Two small chromosomal translocations or duplications were identified in this comparison representing possible genomic differences between E. globulus and section Latoangulatae species. Despite these differences, the overall high level of synteny and colinearity observed between section Maidenaria-Latoangulatae suggests that the genomes of these species are highly conserved indicating that sequence information from the E. grandis genome will be highly transferable to related Symphyomyrtus species.