A chromosome-level genome assembly of Platycladus orientalis and comparative genomics reveal pivotal roles of transposable elements in gene duplication and pseudogenization across gymnosperm giga-genomes

Bao, Yu-Tao

PLANT COMMUNICATIONS

2026

7

8

Wang, XR; Mao, JF;Zhao, W

Gymnosperms, particularly conifers, exhibit a high abundance of transposable elements (TEs) in their gigascale genomes. TEs interact both antagonistically and cooperatively with the host genome, promoting structural and genetic innovations across evolutionary lineages. However, how TEs shape the coding space of gymnosperm genomes remains a key unresolved question. Here, we present a high-quality genome assembly for the keystone conifer Platycladus orientalis, with a contig N50 of 57.54 Mb-the highest continuity reported to date-to investigate the role of TEs. Comparative genomics confirms the absence of recent whole-genome duplication and the presence of genome expansion in gymnosperms, revealing complex interactions among recurrent TE proliferation, low DNA removal rates, and DNA methylation-mediated silencing. Computational evidence indicates that TE-mediated gene duplication and pseudogenization provide a genetic basis for adaptive evolution and functional innovation, significantly shaping gene family dynamics and the emergence of species-specific genes. Additionally, TEs capture and duplicate an average of similar to 400,000 coding gene fragments per gymnosperm genome, facilitating exon shuffling and triggering epigenetic conflicts between source genes and captured exon fragments. Genes from which fragments are captured (donor genes) show significantly higher levels of exon methylation than genes not captured by TEs (free genes), whereas syntenic donor genes exhibit lower levels of silencing responses than nonsyntenic donor genes. This study provides valuable genomic resources and offers insights into the evolutionary patterns and principles underlying the large genome size and complexity of gymnosperms.