Why do spruce take decades to reproduce?
New techniques have enabled researchers in Sweden to begin decoding how one of Northern Europe's most important coniferous tree species switches from growing branches to producing cones – their seed-bearing reproductive organs.
In a recent study that may have implications for the forestry industry, researchers 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 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 called spatial transcriptomics, which allows scientists to see which genes are active in a tissue and exactly where that activity occurs.
“The technology enables us to study the expression patterns of all genes simultaneously,” says the author. 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.
The researchers identified molecular processes active during the vegetative-to-reproductive shift and their specific spatial domains in the shoots. They also identified and experimentally characterized the MADS-box gene DAL55, which is active during lateral organ development.
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?
The authors demonstrate the evolutionary relationships between gymnosperm and angiosperm YABBY genes, responsible for inner or outer cell layers in complex structures.
A researcher in plant biotechnology 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.”
The says the research addresses questions relevant to forestry-dependent economies – such as in Sweden and Finland, where Norway spruce underpins the sector.
The senior author 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,” the author says.
