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Dinosaurs' "Christmas trees" looked the same as ours (free pdf)



From: Ben Creisler
bcreisler@gmail.com

In time for the holidays, a study that shows that the genome of
conifers has changed little since about 100 million years ago. That
means that a Christmas tree today looks the same way that one would
have looked back when the dinosaurs ruled. No clues about decorations,
however. [Presumably, hadrosaurs ate their trees when the holiday was
over.]

The paper is open access:

Nathalie Pavy, Betty Pelgas, Jérôme Laroche, Philippe Rigault,
Nathalie Isabel and Jean Bousquet (2012)
A spruce gene map infers ancient plant genome reshuffling and
subsequent slow evolution in the gymnosperm lineage leading to extant
conifers.
BMC Biology 2012, 10:84
doi:10.1186/1741-7007-10-84
http://www.biomedcentral.com/1741-7007/10/84


Background

Seed plants are composed of angiosperms and gymnosperms, which
diverged from each other around 300 million years ago. While much
light has been shed on the mechanisms and rate of genome evolution in
flowering plants, such knowledge remains conspicuously meagre for the
gymnosperms. Conifers are key representatives of gymnosperms and the
sheer size of their genomes represents a significant challenge for
characterization, sequencing and assembling.

Results

To gain insight into the macro-organisation and long-term evolution of
the conifer genome, we developed a genetic map involving 1,801 spruce
genes. We designed a statistical approach based on kernel density
estimation to analyse gene density and identified seven gene-rich
isochors. Groups of co-localizing genes were also found that were
transcriptionally co-regulated, indicative of functional clusters.
Phylogenetic analyses of 157 gene families for which at least two
duplicates were mapped on the spruce genome indicated that ancient
gene duplicates shared by angiosperms and gymnosperms outnumbered
conifer-specific duplicates by a ratio of eight to one. Ancient
duplicates were much more translocated within and among spruce
chromosomes than conifer-specific duplicates, which were mostly
organised in tandem arrays. Both high synteny and collinearity were
also observed between the genomes of spruce and pine, two conifers
that diverged more than 100 million years ago.

Conclusions

Taken together, these results indicate that much genomic evolution has
occurred in the seed plant lineage before the split between
gymnosperms and angiosperms, and that the pace of evolution of the
genome macro-structure has been much slower in the gymnosperm lineage
leading to extent conifers than that seen for the same period of time
in flowering plants. This trend is largely congruent with the
contrasted rates of diversification and morphological evolution
observed between these two groups of seed plants.

==

news stories:
http://www.eurekalert.org/pub_releases/2012-12/ul-yct121312.php

in French:
http://www.lefil.ulaval.ca/articles/tres-traditionnel-arbre-noel-34372.html