HudsonAlpha Institute for Biotechnology, Huntsville, Alabama 35806, USA.
Department of Plant Biology, University of Georgia, Athens, Georgia 30605, USA.
Genome Biol Evol. 2024 Oct 9;16(10). doi: 10.1093/gbe/evae200.
The genus Asparagus arose ∼9 to 15 million years ago (Ma), and transitions from hermaphroditism to dioecy (separate sexes) occurred ∼3 to 4 Ma. Roughly 27% of extant Asparagus species are dioecious, while the remaining are bisexual with monoclinous flowers. As such, Asparagus is an ideal model taxon for studying the early stages of dioecy and sex chromosome evolution in plants. Until now, however, understanding of diversification and shifts from hermaphroditism to dioecy in Asparagus has been hampered by the lack of robust species tree estimates for the genus. In this study, a genus-wide phylogenomic analysis including 1,726 nuclear loci and comprehensive species sampling supports two independent origins of dioecy in Asparagus-first in a widely distributed Eurasian clade and then in a clade restricted to the Mediterranean Basin. Modeling of ancestral biogeography indicates that both dioecy origins were associated with range expansion out of southern Africa. Our findings also reveal several bursts of diversification across the phylogeny, including an initial radiation in southern Africa that gave rise to 12 major clades in the genus, and more recent radiations that have resulted in paraphyly and polyphyly among closely related species, as expected given active speciation processes. Lastly, we report that the geographic origin of domesticated garden asparagus (Asparagus officinalis L.) was likely in western Asia near the Mediterranean Sea. The presented phylogenomic framework for Asparagus is foundational for ongoing genomic investigations of diversification and functional trait evolution in the genus and contributes to its utility for understanding the origin and early evolution of dioecy and sex chromosomes.
天门冬属约于 900 万至 1500 万年前出现，从雌雄同体到雌雄异株（性别分离）的转变发生在约 300 万至 400 万年前。大约 27%的现存天门冬物种是雌雄异株的，而其余的则是两性花，具有单性雄花。因此，天门冬属是研究植物雌雄异株和性染色体进化早期阶段的理想模式分类群。然而，到目前为止，对天门冬属从雌雄同体到雌雄异株的多样化和转变的理解一直受到缺乏对该属进行稳健的种系发生树估计的阻碍。在这项研究中，包括 1726 个核基因座的全属基因组分析和全面的物种采样支持了天门冬属中雌雄异株的两次独立起源——首先是在一个广泛分布的欧亚分支中，然后是在一个仅限于地中海盆地的分支中。祖先生物地理学的建模表明，雌雄异株的起源都与从南部非洲向外扩张有关。我们的研究结果还揭示了整个系统发育中的几次多样化爆发，包括南部非洲的最初辐射，导致该属中有 12 个主要分支，以及最近的辐射，导致了密切相关物种的并系和多系发生，这与活跃的物种形成过程相一致。最后，我们报告说，经过驯化的花园芦笋（Asparagus officinalis L.）的起源地可能在靠近地中海的西亚。所提出的天门冬属基因组框架为该属的多样化和功能性状进化的正在进行的基因组研究奠定了基础，并有助于其用于理解雌雄异株和性染色体的起源和早期进化。
