PDF(Pubmed)
Abstract：
Heterozygous alleles are widespread in outcrossing and clonally propagated woody plants. The variation in heterozygosity that underlies population adaptive evolution and phenotypic variation, however, remains largely unknown. Here, we describe a de novo chromosome-level genome assembly of Populus tomentosa, an economic and ecologically important native tree in northern China. By resequencing 302 natural accessions, we determined that the South subpopulation (Pop_S) encompasses the ancestral strains of P. tomentosa, while the Northwest subpopulation (Pop_NW) and Northeast subpopulation (Pop_NE) experienced different selection pressures during population evolution, resulting in significant population differentiation and a decrease in the extent of heterozygosity. Analysis of heterozygous selective sweep regions (HSSR) suggested that selection for lower heterozygosity contributed to the local adaptation of P. tomentosa by dwindling gene expression and genetic load in the Pop_NW and Pop_NE subpopulations. Genome-wide association studies (GWAS) revealed that 88 single nucleotide polymorphisms (SNPs) within 63 genes are associated with nine wood composition traits. Among them, the selection for the homozygous AA allele in PtoARF8 is associated with reductions in cellulose and hemicellulose contents by attenuating PtoARF8 expression, and the increase in lignin content is attributable to the selection for decreases in exon heterozygosity in PtoLOX3 during adaptive evolution of natural populations. This study provides novel insights into allelic variations in heterozygosity associated with adaptive evolution of P. tomentosa in response to the local environment and identifies a series of key genes for wood component traits, thereby facilitating genomic-based breeding of important traits in perennial woody plants.
摘要：
杂合等位基因广泛存在于异型和克隆繁殖的木本植物中。构成种群适应性进化和表型变异基础的杂合性变异，然而,仍然很大程度上未知。这里,我们描述了毛白杨的从头染色体水平基因组组装，中国北方的一种经济和生态重要的乡土树。通过重新排序302个自然物种，我们确定，南方亚群（Pop_S）包括毛霉的祖先菌株，而西北亚群（Pop_NW）和东北亚群（Pop_NE）在种群进化过程中经历了不同的选择压力，导致显著的群体分化和杂合度的降低。对杂合选择性扫描区（HSSR）的分析表明，通过减少Pop_NW和Pop_NE亚群的基因表达和遗传负荷，选择较低的杂合性有助于毛斑的局部适应。全基因组关联研究（GWAS）显示，63个基因中的88个单核苷酸多态性（SNP）与9个木材组成性状相关。其中,在PtoARF8中选择纯合AA等位基因与通过减弱PtoARF8表达而降低纤维素和半纤维素含量有关，木质素含量的增加归因于在自然种群的适应性进化过程中选择了PtoLOX3中外显子杂合性的降低。这项研究提供了对杂合性等位基因变异的新见解，该等位基因变异与响应当地环境的毛虫适应性进化相关，并确定了一系列木材成分性状的关键基因，从而促进多年生木本植物重要性状的基因组育种。
