A project to map the genes of spruce and pine trees has revealed that the genome of conifers has remained pretty much the same for more than 100 million years. This stability explains why today’s conifers look like fossil conifers dating to before the age of the dinosaurs.
According to Jean Bousquet, a professor of forestry at the University of Laval in Quebec, conifers were the first plants to evolve after ferns, and fossil records of conifer needles date back 300 million years. That’s about when flowering plants diverged from the conifers. Since then, the flowering plants have undergone major changes, evolving into about 400,000 species, while today there are just 600 species of conifers. The stability of the conifer genome goes hand in hand with its low speciation rate.
“Flowering plants have totally changed their morphology through the years – they include the grasses, shrubs, hardwood trees, vegetables, all kinds of flowers,” Bousquet said. “It’s evolution at a large scale, and we see that in their genome. They have had a lot of reshuffling in their genome, but the conifer genome has remained stable.”
Bousquet speculates that one reason for this stability is that the conifer genome is very large.
“The spruce genome is 20 times the size of the human genome,” he said. “We call it genome obesity. It has become progressively larger over time, and at the same time it has experienced genome paralysis. It is so big that it can’t move or change very quickly.” He considers the large size and unchanging nature of the conifer genome as a sign of genome aging, just like when people age they slow down and gain weight. He notes, however, that genome aging is not a sign that the trees are likely to die out soon.
Details of the research by Bousquet and colleagues at the University of Laval and the Canadian Forest Service were published in the journal BMC Biology. The study was conducted by comparing the genome macrostructure for 157 gene families present in both conifers and flowering plants. While they did find genetic mutations and other small-scale modifications in the conifer genome, the scientists said the macrostructure of the genome has remained stable.
Bousquet thinks this stability occurred in part because the conifers adapted to their environment very early on and haven’t needed to change much. “They survived the glaciations, they survived the dinosaurs, they appear to have achieved a balance with their environment long ago,” he said.
“These plants also have a lot of genetic diversity – among the highest of all plants – which has enabled them to adapt to changing conditions. That’s why they have survived for so long…In contrast, flowering plants are under intense evolutionary pressure as they battle for survival and reproduction.”