Phylogenomics of the genus Glycine sheds light on polyploid evolution and life-strategy transition

Polyploidy and life-strategy transitions between annuality and perenniality often occur in flowering plants. However, the evolutionary propensities of polyploids and the genetic bases of such transitions remain elusive. We assembled chromosome-level genomes of representative perennial species across the genus Glycine including five diploids and a young allopolyploid, and constructed a Glycine super-pangenome framework by integrating 26 annual soybean genomes. These perennial diploids exhibit greater genome stability and possess fewer centromere repeats than the annuals. Biased subgenomic fractionation occurred in the allopolyploid, primarily by accumulation of small deletions in gene clusters through illegitimate recombination, which was associated with pre-existing local subgenomic differentiation. Two genes annotated to modulate vegetative–reproductive phase transition and lateral shoot outgrowth were postulated as candidates underlying the perenniality–annuality transition. Our study provides insights into polyploid genome evolution and lays a foundation for unleashing genetic potential from the perennial gene pool for soybean improvement. Assemblies of six representative perennial Glycine genomes and a comparison with annual soybean genomes reveal evolutionary patterns, differentiation and adaptation of annual and perennial genomes and mechanisms driving subgenome fractionation.