Following an ambitious multi-year effort, researchers have assembled and annotated the genome of the coast redwood, an iconic species and the world’s tallest tree. Sequencing the genome is fundamental to various efforts, including better understanding the tree’s adaptive potential.
As new technologies have developed over the last decade, decoding conifer genomes, which are large and difficult to assemble, has come a long way.
“When we first started, [the coast redwood] was thought to be a genome that might be impossible to sequence with existing technology because of its size and complexity, but we were motivated to take a shot at it,” said Dr. David Neale, a plant sciences professor emeritus at the University of California, Davis and the lead author on the new coast redwood genome research. The results, published in December, were the work of a team from U.C. Davis, Johns Hopkins University and elsewhere.
A genome is all of a living thing’s genetic material—the whole kit and caboodle—and the coast redwood genome is the second largest ever sequenced, at nearly nine times the size of the human genome. The redwood genome has 26.5 billion base pairs of DNA and is hexaploid, meaning it has six sets of chromosomes. Humans have 3 billion base pairs of DNA and are diploid, with two sets of chromosomes.
Though these numbers are impressive, what’s important is the information encoded in the genes, not necessarily the volume of information or how it’s encoded. Sequencing the genome is a step toward understanding the genetic makeup of the trees, including their unique adaptations such as resistance to fungal disease and their relationship to coastal fog.
“If you live in Point Reyes, you know that redwood grows right along the coastal margins, is adapted to fog, and in fact absorbs moisture not only through the root system but through the needles,” Dr. Neale said.
Genomes belong to species, but they also belong to individuals, so every redwood has its own genome, and slight genetic variations can provide an edge when faced with environmental pressures.
In Marin, foresters and conservationists are interested in ecosystem resilience in redwood stands and in harvesting trees, a key component of sustainable forestry. Tom Gaman, a forester from Inverness, says management practices are evolving to include controlled burns, support of old-growth forests, and uneven age management—thinning around the largest and oldest secondary-growth trees.
When trees are planted or thinned, there can be a change to the genetic diversity of that specific redwood population, for better or worse. Using technologies based on the genome sequence can help with monitoring all the way down to an individual tree that might turn out to be particularly resilient when faced with sudden changes in our uncertain climate future.