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Adaptive evolution of the ndhF gene in the genus Rheum(Polygonaceae)

大黄属(蓼科) 植物ndhF 基因的适应性进化(英文)



全 文 :  Guihaia  Jan. 2016ꎬ 36(1):101-106
http: / / journal.gxzw.gxib.cn
http: / / www.guihaia-journal.com
DOI: 10.11931 / guihaia.gxzw201508017
李景剑ꎬ刘合霞ꎬ毛世忠ꎬ等. 大黄属(蓼科)植物 ndhF基因的适应性进化[J]. 广西植物ꎬ 2016ꎬ 36(1):101-106
LI JJꎬLIU HXꎬMAO SZꎬet al. Adaptive evolution of the ndhF gene in the genus Rheum (Polygonaceae)[J]. Guihaiaꎬ 2016ꎬ 36(1):101-106
Adaptive evolution of the ndhF gene in
the genus Rheum (Polygonaceae)
LI Jing ̄Jian1ꎬ2ꎬ LIU He ̄Xia2ꎬ MAO Shi ̄Zhong2ꎬ
ZHAO Bo2ꎬ3ꎬ HUANG Shi ̄Xun2∗
( 1. College of Forestry and Landscape Architectureꎬ South China Agricultural Universityꎬ Guangzhou 510642ꎬ Chinaꎻ 2. Guangxi Institute
of Botanyꎬ Guangxi Zhuang Autonomous Region and the Chinese Academy of Sciencesꎬ Guilin 541006ꎬ Chinaꎻ 3. Institute
of Chinese Materia Medicaꎬ China Academy of Chinese Medical Sciencesꎬ Beijing 100193ꎬ China )
Abstract: Rheumꎬ a highly diversified genus of Polygonaceaeꎬ comprising about 60 speciesꎬ is mainly distributed in the
mountainous and desert regions in Asia and Europe. Its high diversification in the Qinghai ̄Tibetan Plateau and adjacent
areasꎬwhere approximately 40 species have been describedꎬwas suggested to result from the adaptive radiation triggered
by the recent uplifts of the Qinghai ̄Tibetan Plateau and the quaternary climate oscillations. To further understand the
molecular adaptation linked to Rheum radiationꎬ the adaptive evolution of chloroplast ndhF gene belonging to 34 morpho ̄
logically diversified species of the genus Rheum were tested by using the Phylogenetic Analysis Program in this study.
The results showed that the pattern of phylogenic tree was a typical “paralleling” phylogenyꎬ suggesting a radiative di ̄
versification. Three amino acid sites (188Hꎬ465Hꎬ551L) of NDHF subunit were identified under positive selection (ω>
1)ꎬand the secondary structures of NDHF subunit showed that the 188th amino acid was located in the α ̄helix. The
changes of these adaptive sites may be associated with the evolution of NDH to adapt the extreme habitats of Rheum spe ̄
cies caused by the extensive uplifts of the QTP and the quaternary climate oscillations.
Key words: Rheum (Polygonaceae)ꎬ ndhF geneꎬ branch ̄specific modelꎬ site ̄specific modelꎬ positive selection
CLC number: Q941.2    Document code: A    Article ID: 1000 ̄3142(2016)01 ̄0101 ̄06
大黄属(蓼科)植物 ndhF基因的适应性进化
李景剑1ꎬ2ꎬ 刘合霞2ꎬ 毛世忠2ꎬ 赵  博2ꎬ 3ꎬ 黄仕训2∗
( 1. 华南农业大学 林学与风景园林学院ꎬ 广州 510642ꎻ 2. 广西壮族自治区中 国 科 学 院 广西植物研究所ꎬ
广西 桂林 541006ꎻ 3. 中国中医科学院 中药研究所ꎬ 北京 100700 )
摘  要:大黄属(Rheum L.)是蓼科(Polygonaceae)中一个高度分化的大属ꎬ广泛分布在亚洲和欧洲的高山和沙漠
地区ꎬ全世界约 60种ꎬ其中在青藏高原及其邻近地区发现了约 40种ꎮ 该属种的高度分化曾被推测是第三纪末
青藏高原的快速隆升以及第四纪气候的反复变化所引发的适应性辐射导致ꎮ 为进一步了解大黄属植物辐射式
物种分化的分子适应机制ꎬ该研究选取 34个形态上多样化的大黄属物种ꎬ利用系统发育分析软件ꎬ在时间框架
下采用位点模型和分支模型对大黄属的叶绿体 ndhF基因进行了适应性进化分析ꎮ 结果表明:大黄属植物的分
收稿日期: 2015 ̄08 ̄24    修回日期: 2015 ̄12 ̄02
基金项目: 国家科技基础性工作专项(2009FY120200)ꎻ广西自然科学基金(2012GXNSFBA053075)ꎻ广西植物研究所基本业务费(桂植业 14003)
[Supported by the Special Program for Basic Research of Science and Technology of China(2009FY120200)ꎻ the Natural Science Foundation of Guangxi
(2012GXNSFBA053075)ꎻ the Science Research Foundation of Guangxi Institute of Botany (Guizhiye14003)]ꎮ
作者简介: 李景剑(1983 ̄)ꎬ男ꎬ广东廉江人ꎬ博士研究生ꎬ主要从事植物分子生物学研究ꎬ(E ̄mail)calljone@ 163.comꎮ
∗通讯作者: 黄仕训ꎬ研究员ꎬ主要从事濒危植物保护研究ꎬ(E ̄mail)hsx@ gxib.cnꎮ
子进化系统树呈现短而平行的辐射式分支式样ꎬ显示出典型的物种快速辐射多样化特征ꎻ用位点模型检验 ndhF
基因是否存在经受正向选择(ω>1)时ꎬ在氨基酸水平上共鉴定出 3个 NDHF亚基的正选择位点(188Hꎬ465Hꎬ
551L)ꎬ对 NDHF亚基的二级结构进行分析后发现编码的 188H氨基酸位于 α螺旋上ꎮ 大黄属植物可能通过这
些结构域的适应性进化ꎬ适应青藏高原的快速隆升以及第四纪气候的反复变化而引发的陆地生态系统改变ꎮ 该
研究结果可为今后对该属植物的实验分析提供首选位点ꎮ
关键词: 大黄属(蓼科)ꎬ ndhF基因ꎬ 分支模型ꎬ 位点模型ꎬ 正选择位点
    The genus Rheum (Polygonaceae) with about 60
speciesꎬprimarily distributed in mountainous and desert
regions of the Qinghai ̄Tibetan Plateau and adjacent are ̄
as (Kao & Chengꎬ1975ꎻ Liꎬ1998). The distribution
and the ancestral area reconstruction analyses consist ̄
ently suggested that rapid radiations of Rheum have oc ̄
curredꎬand may have been caused by the extensive up ̄
lifts of the Qinghai-Tibetan Plateau (Wang et alꎬ2005ꎻ
Wan et alꎬ2011ꎻ Sun et alꎬ2012). To adapt to the new
alterations of habitatꎬmorphological traits of this genus
are highly diversified. Some species have evolved into
dwarf plants with coriaceous basal leaves or drooping
bracts to defense them from freeze injury and could dis ̄
tribute up to snow line at altitude of 5 400 mꎬfor exam ̄
ple R. Nobile (Xieꎬ2000). For other speciesꎬstem leav ̄
es are have degenerated and basal leaves are covered
with verruca or indumentum to reduce water transpira ̄
tionꎬto avoid the burning from high temperature and to
avoid damage by strong windsꎬthereforeꎬ these species
can grow in the Gobi Desert at altitude 700 m. R. palae ̄
stinum in particularꎬhas broadꎬrigid leavesꎬwith a waxy
surfaceꎬand channels cut into them that funnel any wa ̄
ter that drops onto them toward its rootꎬ with enough
force to cause deep soil penetration (Lev ̄Yadun et alꎬ
2009). These changes in morphology and physiology
might be resulted from the adaptive evolution of some
genes which encode functional proteinsꎬsuch as chloro ̄
plast ndhF gene that related to photosynthesis and pho ̄
torespiration (Zapata et alꎬ2005).
Chloroplast is thought to be a very conservative
part of plant genome but little is known about the evolu ̄
tion of this plastome promoters. Previous study showed
that the alignment of sequences upstream ndhF sugges ̄
ted that promoters of this gene underwent comparatively
rapid evolution in flowering plants ( Seliverstov et alꎬ
2009). The ndhF gene is located in a small single ̄copy
region of the chloroplast genome that rarely underwent
substantial rearrangements in terrestrial plants (Hiratsu ̄
ka et alꎬ1989). Its nucleotide sequence predicts a hy ̄
drophobic protein of 664 amino acids with a calculated
mass of 72.9 kDa (Schluchter et alꎬ1993). The ndhF
gene encodes NADH dehydrogenase F subunit of the
plastid NDH complex which regulated the activity of
NDH complexes by its phosphorylation. The plastid
NDH complex in chloroplast thylakoid membranes is in ̄
volved in photosystem I cyclic and chlororespiratory e ̄
lectron transport in photosynthetic regulation of higher
plants (Lascano et alꎬ2003).
Considering the adaptability of Rheum to extreme
habitatsꎬthe sequences of ndhF gene from 34 species of
Rheum and 2 species of Oxyria in Polygonaceae were re ̄
trieved from the National Center for Biotechnology Infor ̄
mation (NCBI) for adaptive evolution testing in this
study. Our finding may provide new molecular evidence
for the rapid putative radiations of Rheum triggered by
the recent uplifts of the Qinghai ̄Tibetan Plateau.
1  Materials and Methods
Thirty ̄four species of Rheum and two species of
Oxyria in Polygonaceae used in this study were listed in
Table 1. Sequences of ndhF gene were downloaded from
NCBI (http:/ / www.ncbi.nlm.nih.gov / guide / ). Sequence
alignments were conducted using the software CLUSTAL
W ver. 1.83 (Thompson et alꎬ1994) and adjusted manu ̄
ally in BioEdit 5.0.9.1 (Hallꎬ1999). Oxyria digyna and
O. sinensis were used as outgroup. Maximum Parsimony
(MP) analysis was conducted using PAUP 4.0b10 (Swof ̄
fordꎬ 2003)ꎬ Heuristic searches were conducted 1 000
times with random taxon ̄addition sequencesꎬwith tree ̄bi ̄
section ̄reconnection (TBR) branch swappingꎬand with
the options MULPARS in effect and STEEPEST DE ̄
201 广  西  植  物                                  36卷
SCENT off. Support for internal nodes was estimated with
bootstrap values (Felsensteinꎬ1985).
Table 1  Species names and accession
numbers of ndhF sequences
No. Species GenBankNo. No. Species
GenBank
No.
1 Rheum acuminatum FJ872086 19 R. palaestinum FJ872084
2 R. alexandrae EU840401 20 R. palmatum EU840398
3 R. alpinum EU840385 21 R. przewalskyi EU840379
4 R. altaicum EU840404 22 R. pumilum EU840389
5 R. australe EU840393 23 R. mreticulatum EU840383
6 R. compactum EU840403 24 R. rhaponticum EU840402
7 R. delavayi FJ872085 25 R. rhizostachyum EU840380
8 R. forrestii EU840388 26 R. rhomboideum EU840378
9 R. franzenbachii EU840405 27 Rheum sp. EU840392
10 R. globulosum EU840386 28 R. spiciforme EU840377
11 R. hotaoense EU840406 29 R. sublanceolatum EU840390
12 R. kialense EU840387 30 R. tanguticum EU840399
13 R. lhasaense EU840395 31 R. tataricum EU840407
14 R. likiangense EU840396 32 R. tibeticum EU840391
15 R. moorcroftianum EU840384 33 R. webbianum EU840381
16 R. nanum EU840397 34 R. wittrockii EU840400
17 R. nobile EU840382 35 Oxyria digyna EU840375
18 R. officinale EU840394 36 O. sinensis JQ342161
    Based on the MP treeꎬthe analysis of adaptive evo ̄
lution of ndhF gene was implemented in the program of
CODEML from PAML package version 4 (Yangꎬ2007).
The lnL values under one ̄ratio model as well as free ra ̄
tio model were calculatedꎬand the Likelihood Ratio Test
(LRT) was conducted to test whether there were differ ̄
ent ratios for each lineage. Site ̄specific modelsꎬwhich
allowed the ω ratio to vary among sites but fixed a single
ω ratio in all branchesꎬwere used to detect positive se ̄
lection and to identify positively selected sites. Three
pairs of site ̄specific models were calculated to test for
recurrentꎬdiversifyingꎬ selection: M0 ( one ratio) and
M3 (Discrete)ꎬM1 (Neutral) and M2 (Selection)ꎬand
M7 (Beta) and M8 (Beta & ω). (Yang & Nielsenꎬ
2002ꎻ Yang et alꎬ2005). Log likelihoods of models (M1
vs. M2ꎻ M0 vs. M3ꎻ M7 vs. M8) were compared using
LRT.
For the spatial analysis of the codon site under pos ̄
itive selectionꎬthe PSIPRED server (http: / / bioinf. cs.
ucl.ac.uk / psipred / ) was used to analysis the secondary
structure of NDHF subunit for Rheum palaestinum.
2  Results and Analysis
The ndhF dataset had an aligned length of 1 944
characters in the datasetꎬof whichꎬ1 751 characters were
constantꎬ111 were variable and parsimony ̄uninforma ̄
tiveꎬand 82 were parsimony ̄informative. Maximum Par ̄
simony analysis yielded 84 equally parsimonious treesꎬ
and a strict consensus tree of these trees was shown in
Fig.1. The topology of MP tree was consistent with the
molecular phylogenies published to date (Wang et alꎬ
2005ꎻ Sun et alꎬ2012). The consensus tree revealed
three major clades (AꎬBꎬC) within the genus Rheumꎬ
all species of Rheum comprised a well ̄supported line ̄
ageꎬwith a sister relationship to Oxyria.
To analyze the possibility that positive selection
acts on ndhF genesꎬwe used the maximum ̄likelihood
codon model from the CODEML program in the PAML4
package. The topology of the MP tree mentioned above
was modified for all CODEML analyses. All calculations
and tests are listed in Tables 2 and 3. Under the one ̄ra ̄
tio model which allowed for only a single ω ratio across
all sites of the gene phylogeny and the same ω ratio for
all branches in the phylogenic tree (Fig. 1)ꎬthe log ̄
likelihood value was ω = 0.296 5ꎬlower than 1 (Table
2). In the branch ̄specific analysisꎬthe LRT statistic for
the comparison of the one ̄ratio model vs. the free ̄ratio
model was 2Δℓ=77.467 0 with P<0.05 and df=54ꎬsug ̄
gesting that there had different ratios for each lineage of
Rheum species (Table 3). But no sites with a Bayesian
posterior probability of positive selection larger than 0.
95 in one or more cases were found when analyzed by
Bayes.
In site ̄specific modelsꎬmodels M2ꎬM3 and M8 al ̄
lowed sites with ω>1. The LRT statistic of M0 ̄M3ꎬM1 ̄
M2 and M7 ̄M8 comparison all with P<0.05ꎬso models
M3ꎬM2 and M8 was significantly better than M0ꎬM1
and M7. Under both M2 and M8 modelsꎬthree sites were
under positive selection with ω>1 and identified three
NDHF residues (188Hꎬ465Hꎬ551L) with a Bayesian
posterior probability of positive selection larger than
0.95 in one or more cases when analyzed by Empirical
Bayes (Table 2).
3011期                      李景剑等: 大黄属(蓼科)植物 ndhF基因的适应性进化
Fig. 1  Strict consensus tree from maximum ̄parsimony (MP) analysis based on ndhF sequences of Rheum Numbers above the
branches indicate bootstrap values by MP analysis. Numbers with bootstrap values > 50% are shown. Shadows on the right indi ̄
cate five clades of Rheum displaying rapid radiation.
With no obvious sequence similarity to structures pres ̄
ent in PDBꎬthe secondary structure of NDHF subunit for
Rheum palaestinum was predicted by PSIPRED server
(Fig. 2). The test results showed the 188th amino acid
which located in the α ̄helix was histidine (H) in R.
palaestinumꎬwhile asparagine (N) was also found in
other species of Rheum. The amino acid encoded by the
465th codon was histidine (H) in R. palaestinumꎬwhile
asparagine (N) and tyrosine (Y) was found in other
species of Rheum. In additionꎬthe 551th codon encoded
was leucine (L) in R. palaestinumꎬwhile phenylalanine
(F) was found in other species of Rheum.
3  Discussion
The distribution and the ancestral area reconstruc ̄
tion analyses suggests that rapid putative radiations of
Rheum might have been triggered by the recent uplifts of
the Qinghai ̄Tibetan Plateau and the Quaternary climate
oscillations. Geological evidence indicates that at least
four different periods at the early Miocene ( i.e.ꎬ22ꎬ15
-13ꎬ8-7ꎬand 3.5-1.6 Ma) occurred during recent ex ̄
tensive uplifting of the Qinghai ̄Tibetan Plateau ( Shi et
alꎬ1998ꎻ Sun et alꎬ2012)ꎬand new habitats may have
been created while old ones became fragmented within
each period. The new alterations of habitat of Rheum
species are variousꎬfrom snow line at altitude 5 400 m to
Gobi Desert at altitude 700 m. Through the adaptive e ̄
volution of ndhF gene involved in photosynthesis path ̄
waysꎬsome species of Rheum could adapt the extreme
habitats.
By comparing Models M1a / M2a and M7 / M8ꎬthree
401 广  西  植  物                                  36卷
Table 2  Maximum likelihood parameter estimates for ndhF gene
Model np ℓ Estimates of parameter Positively selected site
M0: one ̄ratio 57  ̄4205.9904 ω=0.2965 None
Branch ̄specific models — — — —
F: free ̄ratio 111  ̄4167.2569 — Not allowed
Site ̄specific models — — — —
M1: neutral 58  ̄4162.9674 P0 =0.7513ꎻ P1 =0.2487 Not allowed
M2: selection 60  ̄4154.5725 P0 =0.8588ꎻ P1 =0.0900ꎻ
P2 =0.0512ꎻ ω=3.6640
22Mꎬ24Lꎬ42Tꎬ110Fꎬ169Fꎬ
178Fꎬ188H∗ꎬ243Vꎬ461Pꎬ462Iꎬ
465H∗ꎬ470Kꎬ472Pꎬ476Rꎬ487Nꎬ
495Sꎬ551L∗∗ꎬ555Sꎬ602Gꎬ611V
M3: discrete (K=3) 61  ̄4154.4436 P0 =0.9010ꎻ P1 =0.0890ꎻ
P2 =0.0100ꎻ ω0 =0.1081ꎻ
ω1 =2.2318ꎻ ω2 =6.1884
Not allowed
M7: βꎬneutral 58  ̄4163.5194 a=0.0050ꎻ b=0.0114 Not allowed
M8: β and ω selection 60  ̄4154.6300 P0 =0.9360ꎻ P1 =0.0640ꎻ
a=0.4887ꎻ b=2.7044ꎻ
ω=3.3811
22Mꎬ24Lꎬ42Tꎬ110Fꎬ169Fꎬ
178Fꎬ188H∗∗ꎬ243Vꎬ461Pꎬ
462Iꎬ465H∗ꎬ470Kꎬ472Pꎬ
476Rꎬ487Nꎬ495Sꎬ551L∗∗ꎬ
555Sꎬ590Vꎬ602Gꎬ611Vꎬ628I
  Note: ℓ. Log likelihoodꎻ np. Number of parametersꎻ ω. Ratio of synonymous / non ̄synonymous substitutionsꎻ P. Proportion of sites estimated to be under positive selection with
ω>1ꎻ aꎬb. parameters of the beta distribution. The positively selected sites were in ∗ and ∗∗ under 95% and 99% posterior probability valuesꎬrespectively.
Fig. 2  The secondary structures of NDHF protein for Rheum palaestinum  The sites (188Hꎬ 465Hꎬ 551L)
under adaptive evolution are marked with red boxes.
amino acid sites (188Hꎬ465Hꎬ551L) were identified
under positive selection. The secondary structure of
NDHF subunit showed thatthe positively selected sites
(465H and 551L) were on the loops. The 188th amino
acid which located in the α ̄helix was histidine (H) in
R. palaestinum ( Fig. 2)ꎬ while asparagine ( N) was
found in other species. The ndhF gene encoded a sub ̄
unit of the plastid NDH complexꎬand this complex as ̄
sembly might be regulated on the pos ̄transcriptional
level in a way that the quantity of whole NDH complexes
5011期                      李景剑等: 大黄属(蓼科)植物 ndhF基因的适应性进化
Table 3  Likelihood ratio test (LRTs) of the variable ω
ratios under different models for ndhF gene
Comparison 2⊿ ℓ Degree of freedom P
M0 vs. F 77.4670∗ 54 P<0.05
M0 vs. M3 103.0936∗∗∗ 4 P<0.001
M1 vs. M2 16.7898∗∗ 2 P<0.01
M7 vs. M8 17.7788∗∗ 2 P<0.01
  Note: ∗Significant difference at the P<0.05 levelꎻ ∗∗ Significant difference at
the P<0.01 levelꎻ ∗∗∗Significant difference at the P<0.001 level.
could be determined by the quantity of one of its sub ̄
unitsꎬe.g. NDHF. The activity of NDH complexes was
also regulated by phosphorylation of the NDHF polypep ̄
tide. Our study found that the ndhF gene was at high ex ̄
pression level under stress conditionsꎬand those stress
factors from environment might be the selective pressure
to lead the adaptive evolution of ndhF gene. Our results
indicated that the change of spatial structure may have a
relationship with the adaptation of Rheum to the envi ̄
ronment. For exampleꎬR. palaestinum with histidine mu ̄
tation on the 188th codon site is the rare Rheum plant
growing in mountainous desert areas (receiving an aver ̄
age annual rainfall of ca. 75 mm) in the worldꎬand it
has a single deep main vertical root ( Zoharyꎬ1966).
Previous studies released that histidine is one of the es ̄
sential amino acids for plant growth and survivalꎬespe ̄
cially for root meristem maintenanceꎬthe higher histidine
content in plantꎬthe faster root growth and better adapt ̄
ability to the environments (Moꎬ2006ꎻ Malki & Jaeobsꎬ
2001). So the adaptive evolution of ndhF subunit might
be important for Rheum species to adapt various habi ̄
tats.
Acknowledgements  We are grateful to LIU Lei
for his help with data analysis and Qian Guo for lan ̄
guage editing support.
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