Genomic variation, environmental adaptation and feralization in ramie, an ancient fiber crop.

Feralization is an important evolutionary process, but the mechanisms behind it remain poorly understood. Here, we use the ancient fiber crop, ramie (Boehmeria nivea (L.) Gaudich.) as a model to investigate genomic changes associated with both domestication and fertilization. We first produced a chromosome-scale de novo genome assembly of feral ramie and investigated structural variations between feral and domesticated ramie genomes. Next, 915 accessions from 20 countries were gathered, comprising cultivars, major landraces, feral populations and wild progenitor. Based on whole genome resequencing of these accessions, the most comprehensive ramie genomic variation map to date was constructed. Phylogenetic, demographic, and admixture signal detection analyses indicate that feral ramie is of exoferal or exo-endo origin, i.e., descended from hybridization between domesticated ramie and wild progenitor or ancient landraces. Feral ramie has greater genetic diversity than wild or domesticated ramie, and genomic regions affected by natural selection during feralization are different from those under selection during domestication. Ecological analyses showed that feral and domesticated ramie have similar ecological niches which are substantially different from the niche of the wild progenitor, and three environmental variables were associated with habitat-specific adaptation in feral ramie. Our findings advance our understanding of feralization, providing a scientific basis for the excavation of new crop germplasm resources and offering novel insights into the evolution of feralization in nature.