A new gene atlas of Norway spruce cones tracks the switch from branch to cone and turns up DAL55, a gene no one had described.
Plant an apple tree and it may fruit within a few years. A Norway spruce is in no such hurry, taking more than 25 years to make its first cone and only a fresh batch every three to five years after that.
Now researchers in Sweden have mapped how a young spruce shoot switches from growing branches to building cones. In doing so, they found a gene no one had described before.
What they built is a first draft of a map, not a finished manual. Still, it opens a part of the tree’s life that’s been almost impossible to watch.
Breeders wait decades for spruce
Norway spruce covers large areas of northern Europe, and it’s one of the region’s most valuable trees, cut for timber, construction lumber, and paper.
Foresters would like to breed better ones, the way farmers breed better wheat, by choosing trees that grow fast or hold up in a warming climate.
The trouble is time. A spruce can spend more than 25 years as a juvenile before it’s old enough to reproduce, and even then it sets cones only every few years. So each round of breeding stretches across decades.
Its genome doesn’t help either. A spruce carries an enormous set of DNA, and that sheer size has kept the details of cone-making mostly out of reach.
Watching genes switch on
Every cell in the tree carries the same genes, but a cell in a needle and a cell in a cone use different ones. The team wanted to see which genes were switched on, and exactly where, as a shoot began to change over.
To do it, they used a method developed at KTH Royal Institute of Technology. It reads which genes are active in a piece of tissue, while tracking exactly where each reading comes from. The method is called spatial transcriptomics.
“The technology enables us to study the expression patterns of all genes simultaneously,” said Stefania Giacomello, an associate professor at KTH.
For the readings, they sliced developing shoots into sections just 10 micrometers thick, far thinner than a human hair.
They sampled 88 of these sections at three points across the fall, in August, September, and October, so they could follow the switch as it happened.
Some shoots came from a natural mutant, called acrocona, that starts making cones years earlier than a normal tree.
One gene had escaped notice
As the team compared the readings, one gene stood out because its role had not been described before. They named it DAL55.
It belongs to a family of genes that plants rely on to build flowers, cones, and other reproductive parts.
DAL55 was barely active in August, when the shoots were still simple. It grew steadily busier through September and October, as the cones’ parts took shape.
That timing, and where in the shoot it switched on, pointed to a role in building the cone’s structures. Those are the woody scales that later hold the seeds, and the small bracts beneath them.
Identifying a previously undescribed gene involved in cone development matters, because the tree’s toolkit is still mostly a list of unknowns.
Each named part gives breeders and biologists something concrete to test.
Cones and flowers share old genes
This study also speaks to a much older question. Flowering plants, such as apple and cherry trees, and cone-bearing trees like spruce split from a common ancestor hundreds of millions of years ago.
Some of the genes that control reproduction look alike in both groups, which hints that both inherited them from that shared ancestor.
The spruce study is one example. A group called YABBY genes helps build the inner and outer layers of complex plant parts, and their history appears to link tissue patterns across the seed plants.
Plant scientists at Umeå University and Uppsala University joined the effort.
Jens Sundström, a plant biotechnology researcher at the Swedish University of Agricultural Sciences, or SLU, said the payoff reaches well beyond one tree.
“The findings improve our understanding of the evolutionary processes that contributed to the development of all living seed plants, including both flowering plants and conifers,” he said.
Can this speed up spruce breeding?
The researchers hope the map will help. Knowing which genes control cone formation could, in principle, let breeders spot trees likely to reproduce sooner, or raise seedlings better suited to a shifting climate.
There’s a bigger reason to care. The conifers that dominate the boreal forest are under strain as the climate shifts, and keeping mixed forests healthy is one way the region hopes to cope.
“By learning more about the molecular mechanisms that regulate cone formation, we hope to accelerate breeding efforts and facilitate the production of climate-adapted spruce seedlings for forest owners across the country,” Giacomello said.
For now, those remain hopes. The study maps the genes, and any real breeding payoff would take much more work, and much more time.
It’s also an early map. The method reads small clusters of cells at once, so it cannot yet tell one cell from the next, and some of the finer detail inside the shoot stays blurred.
No one yet knows exactly what DAL55 does inside a cell, only when and where it turns on. Pinning down its job means switching it off in a living tree and watching what happens.
That’s slow work in a plant that takes decades to reproduce, which is exactly why the map had to come first.
The full study was published in the journal Cell.
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