Format: ORAL

Pengchuan Sun1, Susanne S. Renner2, and Jianquan Liu1

1 College of Life Sciences, Sichuan University, Chengdu, China 2 Department of Biology, Washington University, Saint Louis, USA

Chromosome-scale genomes provide a basis for inferringancestral linkage groups and processes of karyotype evolution. We have reconstructed the karyotypes of nine representatives of the major groups of gymnosperms, using an approachthat starts from retained intact chromosomes and syntenic blocks.The results show thatthe most recent common ancestor of the gymnosperms had 24 unique protochromosomes and that their fusion can be traced from the Pinales ancestor to extant species of (((Pinus, Cycas, Ginkgo),((Cupressus, Metasequoia), (Taxus, and Torreya))). The karyotypes of Gnetum and Welwitschia, by contrast, are extremely modified. Recent assessments of cycad and Ginkgo male and female reproductive organ development, pollen ontogeny and germination as well as ovule development, female gametophyte formation, and ovule integument differentiation (Offer et al. Critical Rev. in Plant Science 2023) support the (cycad, Ginkgo) sister relationship.