Nearly complete genome assembly of a critically endangered pine illuminates evolution and conservation of conifers

Abstract

Conifers are dominant in most temperate and boreal forest ecosystems, and are the most widely distributed of the gymnosperms. Despite this, many conifer species are threatened with extinction, and in particular the genetic mechanisms underlying their endangerment remain largely unknown. Pinus squamata, which harbors an extremely large diploid genome and conservation significance, is among the 100 most endangered species (plants and animals) globally, and has been designated as 'Critically Endangered' on the IUCN Red List. In this study, we report an almost complete genome sequence for P. squamata generated by a suite of sequencing technologies, with an assembly of 29.2 Gb, a scaffold N50 length of 2.5 Gb, and a remarkable contig N50 length of 915.4 Mb. This represents the largest and most high-quality gymnosperm genome sequenced to date. The genome is characterized by an ultra-low rate of heterozygosity, is dominated by transposable elements, and contains 55,413 protein-coding genes. Our study provides the first detailed examination of chromosome organization in P. squamata, revealing Rabl configurations and distinctive centromere signatures. This genomic milestone not only deepens our understanding of gymnosperm genetics and evolution but also lays a solid foundation for the development of effective conservation measures, ensuring the survival of this rare species in the face of environmental challenges.