Gene Atlas Reveals How Norway Spruce Finally Learns to Flower

For foresters and tree breeders, Norway spruce is both a cornerstone and a source of chronic frustration. The species anchors the timber economies of Sweden and Finland, supplying wood for construction, paper and countless forest products, yet it refuses to reproduce on anything resembling a convenient schedule. A young spruce may spend more than a quarter of a century in its juvenile phase, building branches and needles without producing a single cone. Even once maturity arrives, cone crops appear only every three to five years. A new study from researchers at KTH Royal Institute of Technology, published in the journal Cell, now offers the most detailed look yet at the genetic machinery behind this famously slow transition from growth to reproduction.

The research team, working in collaboration with the Swedish University of Agricultural Sciences (SLU), constructed a gene atlas of the Norway spruce cone, a map that records when and where individual genes are switched on as the tree’s seed-bearing reproductive organs take shape. The atlas identifies key genes involved in cone development and, in a surprise to the researchers themselves, uncovered an entirely previously unknown gene, designated DAL55. Together, these results begin to decode the molecular switch that tells a spruce to stop investing in vegetative growth and start building the structures that carry seeds.

What makes the achievement remarkable is the sheer difficulty of the study organism. Conifers such as Norway spruce carry among the largest genomes in the plant kingdom, orders of magnitude bigger than the human genome, and their long life cycles make classical genetic experiments slow and cumbersome. Generations cannot be crossed quickly, and the infrequency of cone production means that even obtaining the right tissue at the right developmental stage is a logistical challenge. These obstacles have left fundamental questions about cone development unanswered, despite the species’ enormous ecological and economic importance across Northern Europe.

The methodological heart of the study is a technology called spatial transcriptomics, developed at KTH and since commercialized as Visium by 10x Genomics. Conventional gene-expression measurements tell researchers which genes are active in a sample, but they destroy the spatial context, blending the signals of many different cell types into a single average. Spatial transcriptomics preserves that context. It allows scientists to see which genes are active in a tissue and exactly where that activity occurs, effectively producing a molecular map layered directly onto the anatomy of the organ being studied.

Stefania Giacomello, associate professor at the Department of Gene Technology at KTH, emphasized the power of this approach for the spruce work. The technology, she said, enables the study of the expression patterns of all genes simultaneously. To achieve this, the researchers cut sections of spruce cone tissue to extraordinary thinness, just 10 micrometers, or 0.01 millimeters, and measured gene activity across those sections. The result is a spatiotemporal record of reproductive development: not merely a list of genes involved in cone formation, but a picture of how genetic programs unfold across the tissue as the cone grows and differentiates.

The practical motivation behind the research is straightforward. Forest tree breeding depends on the ability to produce seed, and in spruce the long juvenile period and erratic flowering make that production inefficient. Breeders seeking to develop improved varieties, whether for timber quality, growth rate or resilience, are constrained by how rarely their breeding material sets cones. By identifying the genes that govern the transition from vegetative to reproductive development, the new atlas provides molecular targets that could eventually help breeders induce or accelerate cone formation, shortening breeding cycles that currently stretch across decades.

Giacomello pointed to the climate dimension of this goal. By learning more about the molecular mechanisms that regulate cone formation, she said, the team hopes to accelerate breeding efforts and facilitate the production of climate-adapted spruce seedlings for forest owners across the country. As warming shifts the conditions under which Northern European forests grow, the demand for seedlings bred from trees suited to future climates is expected to rise. A faster, more controllable route to reproductive maturity in spruce would directly support that effort, allowing desirable genetic combinations to be captured in seed more quickly than natural flowering schedules permit.

The study also reaches beyond forestry into one of the deepest questions in plant evolutionary biology. Flowering plants, the angiosperms, dominate the modern landscape, but cone-bearing trees such as spruce belong to the gymnosperms, a far older lineage. Both groups descend from a common seed-plant ancestor, and a central open question is whether some of the genetic mechanisms that control reproduction in flowering plants, including familiar crops and trees such as apple, were inherited from that shared ancestor rather than invented independently along the flowering lineage. Comparing the gene programs active in spruce cones with those known from flowers offers a way to test this.

Jens Sundström, a researcher in plant biotechnology at SLU, framed the findings in these evolutionary terms. The results, he said, improve understanding of the evolutionary processes that contributed to the development of all living seed plants, including both flowering plants and conifers. In other words, the cone atlas is not only a breeding tool; it is a window into the ancient genetic toolkit that has governed seed production for hundreds of millions of years. Shared patterns of gene activity between cones and flowers would suggest deep conservation of reproductive control, while differences would point to lineage-specific innovations in each group.

Sundström also stressed the relevance of the work to economies that depend on forestry, singling out Sweden and Finland, where Norway spruce underpins the sector. For those countries, the gap between a fundamental genetic discovery and a commercial seed orchard may still be long, but the direction of travel is clear. A species that once resisted molecular study because of its giant genome and glacial life cycle has now yielded a high-resolution map of its reproductive development, complete with a new gene to investigate. The decades-long wait for a spruce to reproduce may not be shortened overnight, but the genetic instructions behind that wait are, for the first time, coming into view.

Subject of Research: Genetic regulation of the vegetative-to-reproductive transition and cone development in Norway spruce

Article Title: Why do spruce take decades to reproduce? A genetic study offers some clues

Article References: Why do spruce take decades to reproduce? A genetic study offers some clues. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Norway spruce, spatial transcriptomics, cone development, gene atlas, conifer reproduction, forestry breeding, DAL55, gymnosperms, plant evolution, KTH Royal Institute of Technology, SLU, climate-adapted seedlings