Polycomb Repressive Complex 2-mediated histone modification H3K27me3 is associated with embryogenic potential in Norway spruce

Epigenetic reprogramming during germ cell formation is essential to gain pluripotency and thus embryogenic potential. The histone modification H3K27me3, which is catalysed by the Polycomb repressive complex 2 (PRC2), regulates important developmental processes in both plants and animals, and defects in PRC2 components cause pleiotropic developmental abnormalities. Nevertheless, the role of H3K27me3 in determining embryogenic potential in gymnosperms is still elusive. To address this, we generated H3K27me3 profiles of Norway spruce (Picea abies) embryonic callus and non-embryogenic callus using CUT&RUN, which is a powerful method for chromatin profiling. Here, we show that H3K27me3 mainly accumulated in genic regions in the Norway spruce genome, similarly to what is observed in other plant species. Interestingly, H3K27me3 levels in embryonic callus were much lower than those in the other examined tissues, but markedly increased upon embryo induction. These results show that H3K27me3 levels are associated with the embryogenic potential of a given tissue, and that the early phase of somatic embryogenesis is accompanied by changes in H3K27me3 levels. Thus, our study provides novel insights into the role of this epigenetic mark in spruce embryogenesis and reinforces the importance of PRC2 as a key regulator of cell fate determination across different plant species.