两栖蓼的分子系统学研究

Phylogeny of Polygonum amphibium inferred from molecular sequences

关键词:  两栖蓼  ITS序列  trnL-F序列  春蓼组

Key words:   Polygonum amphibium  ITS sequences  trnL-F sequences  sect. Persicaria

摘要:

两栖蓼是一种水陆两栖植物,植株在不同生态环境下外部形态差异较大,同时两栖蓼的系统位置存在争议,被归入春蓼组(sect. Persicaria)或提升为两栖蓼组(sect. Amphibium)。该文选取两栖蓼及春蓼组植物12种,以及刺蓼组、头状蓼组、神血宁组、拳参组、萹蓄组和外类群掌叶大黄共23种植物进行研究。植物总DNA的提取采用改进的CTAB法,所测序列以及从Genbank数据库下载的序列,以掌叶大黄为外类群,采用最大简约法和贝叶斯法对核糖体ITS序列和叶绿体trnL-F序列进行了系统发育分析。 ITS序列对位排列的长度为735 bp,包括489个可变位点,272个位点是信息位点。简约法得到9个简约树,步长为1 084,CI指数为0.680,RI指数为0.614。trnL-F序列对位排列的长度为1 121 bp,包括427个可变位点,239个位点是信息位点。简约法寻找到9个简约树,步长为551(CI=0. 911,RI=0.910)。贝叶斯法和简约法得到的树基本一致。分子序列分析结果显示,trnL-F序列树类似于ITS序列树。ITS序列构建的发育树上,两栖蓼与刺蓼组植物、春蓼组其他植物形成3个并列的分支; 在trnL-F序列树上,两栖蓼则与其他春蓼组植物形成两个并列的分支。由此可见,两栖蓼与春蓼组其他植物的亲缘关系较远,成一独立的分支。两个分子证据支持将两栖蓼提升为两栖蓼组的处理意见。此外,两栖蓼的花粉具散沟,与典型的春蓼组的具散孔花粉不一致。再加上两栖蓼水陆两栖的特性,因此支持把两栖蓼提升为两栖蓼组的观点。两栖蓼组的界定为多年生草本,水陆两栖,根状茎横生,生于水中茎漂浮,叶长圆形或椭圆形,生于陆地茎直立,叶披针形或长圆状披针形,托叶鞘为筒状、薄膜质,总状花序穗状,瘦果近圆形,花粉具散沟。

Abstract:

Polygonum amphibium is an amphibious plant which external morphology is distinct under different ecological environment. Terrestrial plants can be converted to aquatic plants, aquatic plants could also be converted to terrestrial plants under appropriate ecological condition. Meanwhile, the systematic position of P. amphibium is in dispute, and the species had been placed within sect. Persicaria or treated as sect. Amphibium. The ribosomal ITS sequences and chloroplast trnL-F sequences are very widely used in plants of phylogenetic investigations, including for the genus Polygonum, and which has provided many new phylogenetic evidences for Polygonum. In this paper, a total of 23 kinds of plants including 12 representatives of sect. Persicaria(P. amphibium), 10 representatives of other sections of Polygoum (sect. Echinocaulon, sect. Bistorta, sect. Cephalophilon, sect. Aconogonon, sect. Avicularia)and one outgroup Rheum palmatum were included in the survey. The total DNA was isolated by improved CTAB methods. The ITS region(ITS1-5.8S-ITS2)was amplified with primers ITS1 and ITS4 described by White et al.(1990). The plastid trnL-F sequences was achieved using primers c and f described by Taberlet et al.(1991). All PCR products were purified using a QIA quick gel extraction kit and then sequenced directly on an ABI3770 automated sequencer. The sequenced sequences and the sequence download from Genbank were analysized. The ITS and trnL-F sequences were aligned separately using the program CLUSTALX1.83. Rheum palmatum was designed as outgroup. Bayesian and maximum parsimony analyses were made on sequences of nuclear ITS and plastid trnL-F data sets using the program MrBayes 3.0b4 and PAUP*4.0b respectively. The sequenced nuclear ITS encompassed 735 bp aligned nucleotide positions, of which 489 sites were variable and 272 sites were parsimony informative. The heuristic search yielded 9 trees that were 1 084 steps long(CI=0.680, RI=0.614). The plastid trnL-F region comprised 1 121 bp nucleotide positions. A total of 427 positions were variable, and 239 sites were potentially parsimony informative. Parsimony-based analysis yielded 9 equally parsimonious trees of 551 steps with CI of 0. 911 and RI of 0.910. The trees constructed by Bayesian and MP analyses were basically congruent. Molecular analyses displayed that the ITS tree was similar to the trnL-F tree. In the ITS tree, Polygonum amphibium and other plants of sect. Persicaria plus sect. Echinocaulon formed three parallel clades; In the trnL-F tree, P. amphibium was sister to the remainder of sect. Persicaria with high bootstrap value. Molecular results could be achieved as follows: P. amphibium had a distant relationship to other plants of sect. Persicaria. In addition, the pollen morphology of P. amphibium was scattered ditch, the pollen morphology of the remaining species of sect. Persicaria were scattered hole. Combined with amphibious characteristics of P. amphibium, we were in agreement with Zhang's view that it was necessary to accord P. amphibium as section rank. sect. Amphibium was defined as herbs perennial, amphibious, rhizomes horizontal, aquatic plants: stems floating,leave blade oblong or elliptic, terrestrial plants: stems erect, leaf blade lanceolate or oblong-lanceolate, ocrea tubular, thinly membranous, inflorescence spicate, achene suborbicular, pollen with scattered ditch.