Why do spruce take decades to reproduce? A genetic study offers new clues

In a recent study that may have implications for the forestry industry, researchers from KTH Royal Institute of Technology report the creation of a genetic map that reveals new insight into the Norway spruce’s transition from vegetative to reproductive development. The resulting gene atlas, developed in collaboration with the Swedish University of Agricultural Sciences (SLU), shows when and where genes are active during cone development and identified key genes involved in the process.

In addition, the researchers discovered a previously unknown gene called DAL55.

With their enormous genomes and long life cycles, Norway spruce trees are notoriously difficult to study. Their juvenile period can last longer than 25 years, followed by infrequent cone production—once every three to five years. This poses obstacles for efficient forest tree breeding. These challenges leave important questions about cone development unanswered, despite the species' ecological and economic importance as a source of timber, construction materials, paper and other forest products.

In an unprecedented investigation, the researchers used a technology developed at KTH called spatial transcriptomics, which allows scientists to see which genes are active in a given tissue and exactly where that activity occurs.

“The technology enables us to study the expression patterns of all genes simultaneously,” says Stefania Giacomello, an associate professor at the Department of Gene Technology at KTH and researcher at SciLifeLab. Now commercialized as Visium by 10x Genomics, the technique was used to study gene expression in extremely thin sections of spruce cone tissue, measuring just 10 micrometers (0.01 millimeters) in thickness.

While the immediate goal was to better understand cone development in spruce, the work also touches on a broader evolutionary question: Are some of the genetic mechanisms that control reproduction in flowering plants (angiosperms, such as apple trees) inherited from a much older common ancestor that flowering plants share with cone-bearing trees (gymnosperms) like spruce?

Jens Sundström, a researcher in plant biotechnology at SLU, says: “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 says the research addresses questions relevant to forestry-dependent economies – such as in Sweden and Finland, where Norway spruce underpins the sector.

Giacomello says the findings could help breeders develop spruce varieties better suited to climate change. 

“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 says.