Estep Matt C, McKain Michael R, Vela Diaz Dilys, Zhong Jinshun, Hodge John G, Hodkinson Trevor R, Layton Daniel J, Malcomber Simon T, Pasquet Rémy, Kellogg Elizabeth A
Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121; Department of Biology, Appalachian State University, Boone, NC 28608;
Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121; Donald Danforth Plant Science Center, St. Louis, MO 63132;
Proc Natl Acad Sci U S A. 2014 Oct 21;111(42):15149-54. doi: 10.1073/pnas.1404177111. Epub 2014 Oct 6.
The role of polyploidy, particularly allopolyploidy, in plant diversification is a subject of debate. Whole-genome duplications precede the origins of many major clades (e.g., angiosperms, Brassicaceae, Poaceae), suggesting that polyploidy drives diversification. However, theoretical arguments and empirical studies suggest that polyploid lineages may actually have lower speciation rates and higher extinction rates than diploid lineages. We focus here on the grass tribe Andropogoneae, an economically and ecologically important group of C4 species with a high frequency of polyploids. A phylogeny was constructed for ca. 10% of the species of the clade, based on sequences of four concatenated low-copy nuclear loci. Genetic allopolyploidy was documented using the characteristic pattern of double-labeled gene trees. At least 32% of the species sampled are the result of genetic allopolyploidy and result from 28 distinct tetraploidy events plus an additional six hexaploidy events. This number is a minimum, and the actual frequency could be considerably higher. The parental genomes of most Andropogoneae polyploids diverged in the Late Miocene coincident with the expansion of the major C4 grasslands that dominate the earth today. The well-documented whole-genome duplication in Zea mays ssp. mays occurred after the divergence of Zea and Sorghum. We find no evidence that polyploidization is followed by an increase in net diversification rate; nonetheless, allopolyploidy itself is a major mode of speciation.
多倍体，尤其是异源多倍体，在植物多样化过程中的作用是一个存在争议的话题。全基因组复制先于许多主要分支（如被子植物、十字花科、禾本科）的起源，这表明多倍体推动了多样化。然而，理论观点和实证研究表明，多倍体系可能实际上比二倍体系具有更低的物种形成率和更高的灭绝率。我们在此聚焦于禾本科须芒草族，这是一组经济和生态上重要的C4物种，多倍体出现频率很高。基于四个串联的低拷贝核基因座序列，为该分支约10%的物种构建了系统发育树。利用双标记基因树的特征模式记录了遗传异源多倍体现象。至少32%的抽样物种是遗传异源多倍体的结果，源自28个不同的四倍体事件以及另外6个六倍体事件。这个数字是最低估计，实际频率可能更高。大多数须芒草族多倍体的亲本基因组在晚中新世分化，这与如今主宰地球的主要C4草原的扩张同时发生。玉米（Zea mays ssp. mays）中记录充分的全基因组复制发生在玉米和高粱分化之后。我们没有发现多倍体化后净多样化率增加的证据；尽管如此，异源多倍体本身仍是物种形成的主要模式。
