Scientists identify gene that steers spruce buds toward cones

A gene called PaSPL1 plays a central role in whether a Norway spruce bud develops into a cone or a new shoot, researchers have found. ERR reports that the study, published in Cell, could help explain how the tree’s future cone crop is determined.

Researchers Stefania Giacomello, Sami Saarenpää and colleagues at the Royal Institute of Technology in Solna studied Acrocona, a mutant form of Norway spruce whose cones grow needles on their lower sections. The unusual mix of cone and shoot features allowed the team to examine which genes are active as a bud develops.

Using spatial transcriptomics, the researchers divided developing mutant buds into very thin cross-sections and identified the active genes in each layer. They found that PaSPL1 has a central role in determining whether a bud becomes a cone or a shoot.

Spruce genetics is difficult to study because the trees have many genes with complex evolutionary histories. Spruce also typically begins producing cones only at 25 to 30 years of age, and does not bear them every year, but at intervals of three to five years.

The tree makes the decision about which buds will become shoots or male and female cones in June or July, one or two summers before the cones appear. Warm, dry summers prompt many buds to develop into cones. Red female cones appear in May and produce seeds, while yellow male cones release pollen carried by the wind.