Norway spruce spatiotemporal programs of conifer reproductive development

Conifers are essential components of forest ecosystems; however, their reproductive development remains largely understudied due to their genomes' complexity. Here, we present a time-resolved spatial transcriptomics (ST) atlas of 88 tissue sections across three time points from developing reproductive and vegetative shoots in wild-type Norway spruce (Picea abies), as well as transition shoots from the acrocona mutant. By studying their different spatiotemporal gene expression dynamics, we identified molecular processes active during the vegetative-to-reproductive shift and their specific spatial domains in the shoots. We also identified and experimentally characterized the MADS-box gene DAL55, which is active during lateral organ development. Moreover, we shed light on the evolutionary relationships between gymnosperm and angiosperm YABBY genes, responsible for inner or outer cell layers in complex structures. Overall, our spatiotemporal atlas identifies genes, pathways, and evolutionary relationships associated with plant reproductive organs, providing a valuable resource for studying conifer reproductive development.