Analyzing the phylogeny of poplars based on molecular data.

Dan Zong,Yao Zhang,Tzen-Yuh Chiang,An-Pei Zhou,Li Dan,Pei-Hua Gan,Xin-Lian Zou,Cheng-Zhong He

doi:10.1371/journal.pone.0206998

Abstract

Methods for constructing trees using DNA sequences, known as molecular phylogenetics, have been applied to analyses of phylogenetic origin, evolutionary relatedness and taxonomic classification. Combining data sequenced in this study and downloaded from GenBank, we sampled 112 (chloroplast data) / 122 (ITS data) specimens belonging to 49 (chloroplast data) / 46 (ITS data) poplar species or hybrids from six (chloroplast data) / five sections (ITS data). Maximum parsimony and Bayesian inference were used to analyze phylogenetic relationships within the genus Populus based on eight chloroplast combinations and ITS regions. The results suggested that Bayesian inference might be more suitable for the phylogenetic reconstruction of Populus. All Populus species could be divided into two clades: clade 1, including subclades 1 and 2, and clade 2, including subclades 3 and 4. Species within clade 1, involving five sections except for Leuce, clustered coinciding with their two specific main geographical distribution areas: China (subclade 1) and North America (subclade 2). Clustering in subclade 3, section Leuce was confirmed to be of monophyletic origin and independent evolution. Its two subsections, namely Albidae and Trepidae, could be separated by chloroplast data but had frequent gene flow based on ITS data. Phylogeny analysis based on chloroplast data demonstrated once more that section Aigeiros was paraphyletic and further showed that the P. deltoides lineage is restricted in subclade 2 and that P. nigra lineage, located in subclade 3, originated from a hybrid of which an Albidae ancestor species was the material parent. Similarly, section Tacamahaca was found to be paraphyletic and had two lineages: a clade 1 lineage, such as P. cathayana, and a clade 2 lineage, such as P. simonii. Section Leucoides was paraphyletic and closely linked to section Tacamahaca. Their section boundaries were not conclusively delimitated by sequencing information.

Highlights

Poplars (Populus L.), one of the world’s most important forest trees, are accepted as model trees due to their high growth, strong adaptability, easy propagation and small genome[1,2,3]
internal transcribed spacer (ITS) region analysis suggested that this region contained 74 informative and 92 variable sites that belonged to a 575-bp aligned sequence
The ITS region dataset showed that the highest inter- and intraspecific distances were in both sections Tacamahaca (0.01093 and 0.00558, respectively), and the lowest values were present in sections Leuce (0.00221) and Leucoides (0.00059)

Summary

Introduction

Poplars (Populus L.), one of the world’s most important forest trees, are accepted as model trees due to their high growth, strong adaptability, easy propagation and small genome[1,2,3]. Eckenwalder classified Populus into 22 species in six sections: Tacamahaca, Aigeiros, Leuce, Leucoides, Turanga and Abaso[4], but the Flora of China recorded 71 species from five sections (except for Abaso)[5]. They are widely distributed across the northern hemisphere[5,6]. China has rich poplar germplasm resources because it is one of the most important poplar distribution areas. To develop and utilize resources as an important foundation for basic and applied research, it is imperative to understand the genetic and phylogenetic relationships among Populus

Methods

Results

Conclusion