Haplotype-resolved genome assembly and resequencing analysis provide insights into genome evolution and allelic imbalance in <i>Pinus densiflora</i>

Abstract

Haplotype-level allelic characterization facilitates research on the functional, evolutionary and breeding-related features of extremely large and complex plant genomes. We report a 21.7-Gb chromosome-level haplotype-resolved assembly in Pinus densiflora. We found genome rearrangements involving translocations and inversions between chromosomes 1 and 3 of Pinus species and a proliferation of specific long terminal repeat (LTR) retrotransposons (LTR-RTs) in P. densiflora. Evolutionary analyses illustrated that tandem and LTR-RT-mediated duplications led to an increment of transcription factor (TF) genes in P. densiflora. The haplotype sequence comparison showed allelic imbalances, including presence-absence variations of genes (PAV genes) and their functional contributions to flowering and abiotic stress-related traits in P. densiflora. Allele-aware resequencing analysis revealed PAV gene diversity across P. densiflora accessions. Our study provides insights into key mechanisms underlying the evolution of genome structure, LTR-RTs and TFs within the Pinus lineage as well as allelic imbalances and diversity across P. densiflora.