Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, MG, 36036-241, Brazil.
Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA.
Am J Bot. 2020 Mar;107(3):466-476. doi: 10.1002/ajb2.1443. Epub 2020 Mar 1.
Plant genomes vary in size and complexity due in part to polyploidization. Latitudinal analyses of polyploidy are biased toward floras of temperate regions, with much less research done in the tropics. Lippia alba has been described as a tropical polyploid complex with diploid, triploid, tetraploid, and hexaploid accessions. However, no data regarding relationships among the ploidal levels and their origins have been reported. Our goals are to clarify the relationships among accessions of Lippia alba and the origins of each ploidal level.
We investigated 98 samples representing all five geographical regions of Brazil and all ploidal levels using microsatellite (SSR) allelic variation and DNA sequences of ITS and trnL-F. Nine morphological structures were analyzed from 33 herbarium samples, and the chemical compounds of 78 accessions were analyzed by GC-MS.
Genetic distance analysis, the alignment block pattern, as well as RAxML and Bayesian trees showed that accessions grouped by ploidal level. The triploids form a well-defined group that originated from a single group of diploids. The tetraploids and hexaploid grouped together in SSR and trnL-F analyses. The recovered groups agree with chemical data and morphology.
The accessions grouped by ploidal level. Only one origin of triploids from a single group of diploids was observed. The tetraploid origin is uncertain; however, it appears to have contributed to the origin of the hexaploid. This framework reveals linkages among the ploidal levels, providing new insights into the evolution of a polyploid complex of tropical plants.
植物基因组的大小和复杂性因多倍体化而有所不同。多倍体的纬度分析偏向于温带地区的植物群，而在热带地区的研究要少得多。香蜂草已被描述为具有二倍体、三倍体、四倍体和六倍体品系的热带多倍体复合体。然而，尚未报道关于各倍性水平及其起源之间关系的数据。我们的目标是阐明香蜂草品系之间的关系以及各倍性水平的起源。
我们使用微卫星（SSR）等位基因变异和 ITS 和 trnL-F 的 DNA 序列，调查了代表巴西五个地理区域和所有倍性水平的 98 个样本。从 33 个标本中分析了 9 个形态结构，通过 GC-MS 分析了 78 个品系的化学化合物。
遗传距离分析、对齐块模式以及 RAxML 和贝叶斯树表明，品系按倍性水平分组。三倍体形成了一个明确界定的群体，起源于单一的二倍体群体。在 SSR 和 trnL-F 分析中，四倍体和六倍体聚集在一起。回收的群体与化学数据和形态学一致。
品系按倍性水平分组。仅观察到三倍体来自单一的二倍体群体。四倍体的起源不确定；然而，它似乎促成了六倍体的起源。该框架揭示了各倍性水平之间的联系，为热带植物多倍体复合体的进化提供了新的见解。
