Guangqi Gao, Luxi Yan, Yu Cai, Yu Guo, Congcong Jiang, Qiang He, Sarah Tasnim, Zongyun Feng, Jun Liu, Jing Zhang, Takao Komatsuda, Martin Mascher, Ping Yang

Plant Communications; 2024; IF:10.50

DOI: 10.1016/j.xplc.2024.100828

Abstract

Tibetan weedy barleys reside at the edges of qingke (hulless barley) fields in Tibet. The spikes of these weedy barleys contain or lack a brittle rachis, with either two- or six rowed spikes and either hulled or hulless grains at maturity. Although the brittle rachis trait of Tibetan weedy barleys is similar to that of wild barley (Hordeum vulgare ssp. spontaneum Thell.), these plants share genetic similarity with domesticated barley. The origin of Tibetan weedy barleys remains debated. Here, we show that most Tibetan weedy barleys originated from the cross-pollinated hybridization of domesticated Journal Pre-proof  barleys, followed by hybrids self-pollination and recombination between Non-brittle rachis 1 (btr1) and 2 (btr2). We discovered the specific genetic ancestry of these weedy barleys in South Asian accessions. Tibetan weedy barleys exhibit lower genetic diversity in comparison to those of wild and Chinese landraces/cultivars, and share a close relationship with qingke, genetically differing from the typical eastern and western barley populations. Tibetan weedy barleys were classified into two groups, brittle rachis (named BR) and non-brittle rachis (NBR); these traits align with the haplotypes of the btr1 and btr2 genes. Whereas wild barleys carry haplotype combinations of Btr1 and Btr2, each showing lower proportions in a population, the recombinant haplotype BTR2H8+BTR1H24 is predominant in the BR group. Haplotype block analysis based on whole-genome sequencing revealed two recombination breakpoints, which are present in 80.6% and 16.8% of BR accessions using marker-assisted diagnosis. Hybridization events between wild and domesticated barley were rarely detected. These findings support the notion that Tibetan weedy barleys originated via recombination between Btr1 and Btr2 in domesticated barley.