全 文 :棉毛橐吾和穗序橐吾的自然杂交研究∗
余姣君1ꎬ2ꎬ 潘 莉3ꎬ 潘跃芝1ꎬ 龚 洵1∗∗
(1 中国科学院昆明植物研究所资源植物与生物技术重点实验室ꎬ 云南 昆明 650201ꎻ
2 中国科学院大学ꎬ 北京 100049ꎻ 3 云南省林业科学院ꎬ 云南 昆明 650201)
摘要: 在棉毛橐吾 (Ligularia vellerea) 和穗序橐吾 (L subspicata) 同域分布的居群中存在形态特征介于两
者之间的个体ꎮ 经分析ꎬ 这些个体有 3种不同的形态类型ꎬ 可能是这两个物种之间的杂交后代ꎮ 为检验这
一假设ꎬ 对所采集的假设亲本和中间个体材料进行了核糖体内转录间隔区 ITS4 ̄5和叶绿体 atpB ̄rbcL测序ꎮ
假设杂交个体的 ITS直接测序结果具明显的叠加性ꎬ 之后的克隆测序也分离出两种与假设亲本种相同的序
列类型ꎬ 因此ꎬ 这些假设杂交个体得到了证实ꎮ 据母系遗传的叶绿体 atpB ̄rbcL 测序结果ꎬ 穗序橐吾同是
它们的质体贡献者ꎬ 即虽然这些杂交个体具不同的形态特征ꎬ 但都是以棉毛橐吾和穗序橐吾为亲本且以穗
序橐吾为质体贡献者的杂交后代ꎮ
关键词: 棉毛橐吾ꎻ 穗序橐吾ꎻ 杂交后代ꎻ 核 ITS4 ̄5ꎻ 叶绿体 atpB ̄rbcL片段
中图分类号: Q 321 1ꎬ Q 78 文献标识码: A 文章编号: 2095-0845(2014)02-219-08
Natural Hybrids between Ligularia vellerea and
L subspicata (Asteraceae: Senecioneae)
YU Jiao ̄Jun1ꎬ2ꎬ PAN Li3ꎬ PAN Yue ̄Zhi1ꎬ GONG Xun1∗∗
(1 Key Laboratory of Economic Plants and Biotechnologyꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ Chinaꎻ
3 Yunnan Academy of Forestryꎬ Kunming 650201ꎬ China)
Abstract: Three types of intermediate morphological individuals were found in the sympatric distribution areas of
Ligularia vellerea and L subspicata. These intermediate individuals were hypothesized to be the hybrids of these two
species based on the detailed comparison of their morphological characters. To test this hypothesisꎬ we compared the
DNA sequence of L vellereaꎬ L subspicata and the intermediate individuals by using the internal transcribed spacer
region of nuclear ribosomal and atpB ̄rbcL intergenic spacer region of the chloroplast. Direct sequencing of ITS clear ̄
ly had additives and then cloned sequencing cloned out two kinds of sequences that were identical to those putative
parental speciesꎬ thus these putative hybrids were approved. With different morphological characters among three
typesꎬ their plastid donors were all L subspicata according to the maternal sequences of atpB ̄rbcL.
Key words: Ligularia vellereaꎻ L subspicataꎻ Hybrid progenyꎻ ITSꎻ atpB ̄rbcL
There are increasingly voices to illustrate the
important role of natural hybridization in plant evolu ̄
tion (Arnoldꎬ 1997ꎻ Riesebergꎬ 1997ꎻ Rieseberg et
al.ꎬ 2000ꎻ Abbott et al.ꎬ 2008ꎬ 2010ꎻ Soltis and
Soltisꎬ 2009ꎻ Chase et al.ꎬ 2010). The consequences
of hybridization may include introgression affecting
one or both taxaꎬ formation of hybrid (especially al ̄
loploid) speciesꎬ and development of reticulate pat ̄
植 物 分 类 与 资 源 学 报 2014ꎬ 36 (2): 219~226
Plant Diversity and Resources DOI: 10.7677 / ynzwyj201413109
∗
∗∗
Funding: The National Natural Science Foundation of China (31170633)
Author for correspondenceꎻ E ̄mail: gongxun@mail kib ac cn
Received date: 2013-05-09ꎬ Accepted date: 2013-07-30
作者简介: 余姣君 (1985-) 女ꎬ 博士研究生ꎬ 主要从事植物多样性起源与演化研究ꎮ
terns of evolution within a group ( Arnoldꎬ 1997ꎻ
Soltis and Soltisꎬ 2009).
The genus Ligularia Cass. consists of about 140
species mainly distributed in eastern Asiaꎬ one ̄hun ̄
dred twenty ̄four species of which are known in Chi ̄
na (Liuꎬ 1989ꎻ Liu et al.ꎬ 1994ꎻ Liu and Illariono ̄
vaꎬ 2011). The majority of Ligularia distributed in
the Hengduan Mountains area are endemic ( Liu et
al.ꎬ 1994ꎻ Liu et al.ꎬ 2006). Interspecific diploid
hybridization was considered to be an important
cause for the high species diversity in this genus
(Liu et al.ꎬ 2001ꎬ 2006). Natural hybrids were
commonly found in certain area which Ligularia
sympatric distributed (Liu et al.ꎬ 2006ꎻ Yu et al.ꎬ
2011). Ligularia×maoniushanensis X. Gong & Y Z.
Pan is the first reported natural hybrid species
through comprehensive studying (Pan et al.ꎬ 2008).
Furthermoreꎬ by comparing L lamarum and L sub ̄
spicata chemical similaritiesꎬ Saito et al. ( 2011)
presumed that the two species hybridized with other
species of this genus commonly. Yu et al. ( 2011)
studied one mix population with 6 Ligularia speciesꎬ
based on morphological and molecular data (cpDNA
and ITS sequencesꎬ ISSR markers)ꎬ bidirectional but
asymmetric hybridization and also backcross was de ̄
tected between L subspicata and L nelumbifonia.
Hybridization is very common in Ligularia with vari ̄
ous form and progenies.
During field collection trips to the Hengduan
Mountains in Yunnanꎬ we found a mixed population
including L subspicata (Bur. et Franch.) Hand. ̄Mazz.ꎬ
L vellerea ( Franch.) Hand ̄Mazz.ꎬ and a putative
natural hybrid occurring on Mt. Daxue. The putative
nothospecies was considered to be a natural hybrid
between L subspicata and L vellerea based on its in ̄
termediate morphological appearance and the partial
overlap of the flowering period. Given this anthesis
overlapꎬ cross ̄pollination between two putative par ̄
ents could occur naturally under sympatric conditions.
In the current studyꎬ the ITS region of the nu ̄
clear ribosomal DNA of all the sampled individuals
was sequenced to determine the hybrid status of the
morphologically taxon. Once its hybrid status was
confirmedꎬ we sequenced chloroplast atpB ̄ rbcL re ̄
gion for three taxa to determine the relationship be ̄
tween these hybrids and the two natural species.
1 Materials and methods
1 1 Material collection and molecular methods
We collected Ligularia vellereaꎬ L subspicata and
the putative hybrids in the mix population on the Dax ̄
ue Mountainꎬ Shangri Countyꎬ Yunnanꎬ China. Young
leaves of 25 individuals (including 10 L vellereaꎬ 10
L subspicata and 5 putative hybrids) were collected
and dried in silica gel in field for DNA extraction.
Though no other Ligularia species was found in this
populationꎬ a set of other species (sequences down ̄
load from NCBIꎬ Appendix) were included to verify
if this population genetic material contaminate by
other species in the phylogenetic analysis. Total ge ̄
nomic DNA was extracted from the silica gel ̄dried
leaf tissue using the cetyltrimethyl ammonium bro ̄
mide (Cruz ̄Mazo et al.ꎬ 2009) methods (Doyle and
Doyleꎬ 1987) with minor modification.
The ITS region of the nuclear ribosomal DNA of
all the sampled individuals was amplified using
primers ITS4 and ITS5 (White et al.ꎬ 1990). PCR
was conducted in a total reaction volume of 20 μLꎬ
containing 10 - 30 ng template DNAꎬ 2 0 μL 10 ×
PCR Buffer with (NH4) 2 SO4ꎬ 1 3 μL MgCl2 (25
mmolL-1)ꎬ 0 5 μL dNTP (2 5 mmolL-1 each)ꎬ
0 3 mmolL-1 each primer and 0 75 unit of Taq pol ̄
ymerase (Takara). Amplifications were performed as
following conditions: 1 cycleꎬ 94 ℃ꎬ 5 minꎻ 30 cy ̄
clesꎬ 94 ℃ꎬ 45 secꎻ 55 ℃ꎬ 1 minꎻ 72 ℃ꎬ 40 secꎬ
followed a final extension of 1 cycleꎬ 72 ℃ꎬ 5 min.
The PCR products were purified by electro ̄phoresis
through a 1 2% agarose gel followed by use of an
E Z N A. Gel Extraction Kit (Omegaꎬ Guangzhouꎬ
China). All accessions were subjected to sequen ̄
cingꎬ with amplification primers in an ABI 3700
DNA automated sequencer with the BigDye Termina ̄
tor Cycle Sequencing Kit (Applied Biosystemsꎬ Fos ̄
ter Cityꎬ Californiaꎬ U S A.) . The sequences were
022 植 物 分 类 与 资 源 学 报 第 36卷
aligned and compared in SeqMan (DNASTARꎬ Bei ̄
jingꎬ China) ( Burlandꎬ 1999). While direct se ̄
quencing is feasible for L vellerea and L subspicataꎬ
it produced chimeric or unreadable peaks in the
chromatogram for the putative hybrids. Henceꎬ clo ̄
ning sequencing was performed subsequently for the
putative hybrid. Purified PCR products were cloned
into plasmids using the pUM ̄T vector system
(Bioteke). Four to twenty positive clones were se ̄
lected for each amplification product and cultured for
isolating plasmids. Positive clones with the inserts of
correct size were confirmed by colony PCR. The
plasmids with correct inserts were sequenced using
ITS4 and ITS5 primers.
All samples from L vellereaꎬ L subspicata and
the putative hybrid were used in the chloroplast
atpB ̄ rbcL. Chloroplast atpB ̄ rbcL region were am ̄
plified using primers atpB and rbcL (Chiang et al.ꎬ
1998). PCR was conducted in a reaction volume of
20 μLꎬ containing 10-30 ng template DNAꎬ 2 0 μL
10×PCR Buffer with ( NH4 ) 2 SO4ꎬ 1 0 μL MgCl2
(25 mmolL-1 )ꎬ 1 0 μL dNTP (2 5 mmolL-1
each)ꎬ 0 3 mmolL-1 each primer and 1 5 unit of
Taq polymerase (Takara). Amplification conditions
were as follows: 1 cycleꎬ 94 ℃ꎬ 4 minꎻ 30 cyclesꎬ
94 ℃ꎬ 45 secꎻ 53 ℃ꎬ 45 secꎻ 72 ℃ꎬ 1 min or 50
secꎬ followed by 1 cycleꎬ 72 ℃ꎬ 7 min. PCR prod ̄
ucts were purified and then directly sequenced bidi ̄
rectional using the methods mentioned above.
1 2 Phylogenetic analysis
Minor variation (usually one or two nucleotide
sites) between some clones may have resulted from
PCR error caused by Taq DNA polymerase. Putative
PCR ̄mediated recombinants were excluded before
further phylogenetic analysis. All sequences were a ̄
ligned in Clustal X (Thompson et al.ꎬ 1997) com ̄
plimented PAUP4 0. Information about variable
sites was obtained using the program DnaSP 4 0
(Rozas et al.ꎬ 2003). The aligned sequences were
used to infer the phylogeny of the sampled individu ̄
als using the criterion of maximum parsimonyꎬ im ̄
plemented in PAUP∗ version 4 0b (Swoffordꎬ 2002).
Parsimony analyses were carried out using a heuris ̄
tic search with tree bisection and reconnection
branch swappingꎬ the Multrees optionꎬ ACCTRAN
optimisationꎬ and 1 000 random addition replicates
for the nuclear and chloroplast datasets.
2 Results
2 1 Morphology
Ligularia vellerea and L subspicata belong to
Ser. Scapicaulis S W. Liu and Ser. Ligularia Cass.ꎬ
respectively (Liuꎬ 1989). The main morphological
differences between the two species are leaf shapesꎬ
hairs on stems and capitula types (Table 1ꎬ Fig 1).
The leaves of L vellerea are ovate with cuneate baseꎬ
whereas those of L subspicata are cordate or hastate.
The stem of L vellerea is full of densely long white
hairsꎬ whereas that of L subspicata is proximally gla ̄
brous. There are 5-7 ray florets in one capitulum of
L vellereaꎬ but none in L subspicata. The putative nat ̄
ural hybrids are intermediate between those of the
putative parental speciesꎬ with ovate or cordate leav ̄
esꎬ with / without ray florets in capitula and with /
without hairs on stem and the morphological charac ̄
ters show three types of apparent transition state.
Type ̄a and type ̄b are similar to L vellereaꎬ but
there are thinner hairs on stem in type ̄a and type ̄bꎬ
and no ray florets in type ̄b. Type ̄c is similar to
L subspicata but with ray florets. The shape form of
their leaves show apparently transition state.
2 2 Phylogenetic analysis based on nrDNA
ITS4 ̄5
The direct sequence aligned matrix generated a
total of 642 bp or 641 bp (because of one indel) . No
variation was detected within species of L vellerea
and L subspicata. There were 15 variation sites be ̄
tween the two putative parental species. The putative
natural hybrids had more than ten double peaksꎬ and
cloned sequences obtained two sequence types that
were identical to those of L vellerea and L subspicataꎬ
respectivelyꎬ which then clearly displaying that all
double copies of ITS came from the putative parental
species (Table 2).
1222期 YU Jiao ̄Jun et al.: Natural Hybrids between Ligularia vellerea and L subspicata (Asteraceae: Senecioneae)
Fig 1 From up to bottom show stems hairsꎬ floretsꎬ laminas and whole individual of putative hybrids and their putative parents respectively.
L vellerea show the ovate with cuneate base leavesꎬ 5-7 ray florets in one capitulum and full of densely long white hairs on stemsꎻ
H ̄a show the cordate leafꎬ with stem leavesꎬ several ray florets in one capitulum and thinner white hairs on stemsꎻ H ̄b show the
cordate leafꎬ with stem leavesꎬ no ray florets in capitulum and densely long white hairs on stemsꎻ H ̄c show the cordate leafꎬ
with stem leavesꎬ several ray florets in one capitulum and glabre stemsꎻ and L subspicata show the hastate or cordate leaves
with stem leavesꎬ no ray florets in one capitulum and glabre stems. Photographs not to scale
Table 1 Main morphological differences characterizing of Ligularia vellereaꎬ L subspicata and three types of putative hybrids
Taxa
Characters
stems clothing stem leaves sexuality of florets composite raceme
Ligularia vellerea densely long white puberulent without stem leaf numerous tubular floretsꎬ with several ray florets
putative hybrid a (H ̄a) sparsely long white puberulent with stem leaves numerous tubular floretsꎬ with several ray florets
putative hybrid b (H ̄b) long white puberulence with stem leaves numerous tubular floretsꎬ without ray floret
putative hybrid c (H ̄c) proximally glabrous with stem leaves numerous tubular floretsꎬ with several ray florets
L subspicata proximally glabrous with stem leaves numerous tubular floretsꎬ without ray floret
222 植 物 分 类 与 资 源 学 报 第 36卷
Table 2 Sites of variation and indels of ITS4 ̄5 from related taxa
Taxa
Polymorphic sites
4
5
1
0
0
1
5
2
157
-
159
1
8
0
2
4
9
254
-
255
2
7
4
3
1
9
4
6
4
4
8
0
4
8
5
5
5
7
5
6
4
6
5
6
A1 ̄5 A T G TCC C C GT G C C C G C C C
A2 ̄5 A C G TCC C C GT G C T T G C C C
A3 ̄1 A C G TCC C C GT A T T C G C C C
B1 ̄3 A C G TCC C C GT G C T T G C C C
C5 ̄2 A C G TCC C C GT G T C C G C C C
S1 ̄S10ꎬ S12 A C G TCC C C GT G C T Y G C C C
A1 W Y R YYM Y - RY A C C C R Y Y C
A2 W C R YYM Y C RY G C Y Y R Y Y C
A3 W C R YYM Y - RY A C C C R Y Y Y
B1 W C R YYM Y C RY A C Y Y R Y Y Y
C5 W C R YYM Y - RY A Y C C R Y Y C
V1 ̄V4ꎬ V6 ̄V10ꎬ V12 T C A CTA T - AC A C C C A T T T
A1 ̄1 T C A CTA T - AC A C C C A T T T
A2 ̄3 T C A CTA T - AC A C C C A T T T
A3 ̄2 T C A CTA T - AC A C C C A T T T
B1 ̄6 T C A CTA T - AC A C C C A T T T
C5 ̄3 T C A CTA T - AC A C C C A T T T
Note: C+T=Y A+C=M A+T=W A+G=R G+T=K C+G=S
Taxa: Aꎬ H ̄aꎻ Bꎬ H ̄bꎻ Cꎬ H ̄cꎻ Sꎬ L subspicataꎻ Dꎬ L vellerea. Numbers following taxon initials are sample numbers and clone numbers (if any).
The strict consensus tree from parsimony analy ̄
sis of 25 individuals was generated to show phyloge ̄
netic relationship among them (Fig 2). The MP tree
indicates that putative parents clustered restively
branches with high bootstrap value. With cloned se ̄
quencesꎬ each individual possessed one copy of one
putative parent and clustered to parent branches ex ̄
actly.
2 3 Phylogenetic analysis based on sequences of
cpDNA atpB ̄rbcL
Direct sequencing of atpB ̄rbcL generated 740
bp for L vellerea and 739 bp for L subspicataꎬ exhib ̄
ited 4 variation sites which included one indels (Ta ̄
ble 3). Among these sitesꎬ there were no polymor ̄
phisms within L subspicata individuals but one ex ̄
ception in L vellerea. All of putative hybrids had the
same atpB ̄rbcL sequences with L subspicata.
The MP tree obtained from the cpDNA atpB ̄
rbcL regions is shown in Fig 3. The putative parental
species formed two separate clusters. All the putative
hybrids clustered together with L subspicata. The
other Ligularia species were clearly separated from
the putative parental species and hybrids. Because
chloroplast DNA is maternally inherited in Ligularia
(Zhang et al.ꎬ 2003)ꎬ these putative hybrids had
L subspicata as the plastid donor. Hence unidirec ̄
tional hybridization was detected between L subspicata
and L vellerea.
Table 3 Sites of variation and indels of chloroplast
sequences from related taxa
Taxa
Polymorphic sites
2
8
4
0
9
5
1
3
6
8
1
S1 ̄S10ꎬ S12 G T - C
A1 G T - C
A2 G T - C
A3 G T - C
B1 G T - C
C5 G T - C
V1 ̄V4ꎬ V6ꎬ V7ꎬ V9ꎬ
V10ꎬ V12 A A
- A
V8 G A A A
Taxa initials and numbering are as in Table 2
3222期 YU Jiao ̄Jun et al.: Natural Hybrids between Ligularia vellerea and L subspicata (Asteraceae: Senecioneae)
3 Discussion
During our field research on Ligularia species
more than decadeꎬ L vellerea and L subspicata are
commonly found coexistꎬ but no intermediate mor ̄
phological individuals were discovered in these sym ̄
patric areas except the one on Mt. Daxue. The puta ̄
tive hybrids grow on an open space in a forest edge
that was previously dominated by fir. Some trees
were destroyed in road building and maintenanceꎬ
and now grassland mainly grows the putative parental
Ligularia species appeared on both sides of the road.
This easily disturbed micro ̄habitat may have promo ̄
ted hybridization between these two species. Such
special circumstances are also more likely to give
rise to new species of hybrid origin (Buerkle et al.ꎬ
2000ꎻ Rieseberg et al.ꎬ 2003ꎻ Gompert et al.ꎬ 2006).
Plant grow on wintry highland requires to evolve
certain common adaptive mechanisms. Ligularia spe ̄
cies often share the same pollinators in the highlands
(Liuꎬ 2002ꎻ Cao et al.ꎬ 2008). When different spe ̄
cies bloom at same place and timeꎬ nectar ̄collecting
insects may transfer one species’ pollen to another spe ̄
cies’ flowers casually. The flowering times of the sym ̄
patric Ligularia species overlapꎬ according to previous
Fig 2 Strict consensus tree from a parsimony analysis of ITS4 ̄5 sequences from putative hybrid individuals and their putative parental species.
Taxa: Vꎬ L vellereaꎻ Sꎬ L subspicataꎻ Aꎬ putative hybrids aꎻ Bꎬ putative hybrids bꎻ Cꎬ putative hybrids c. Numbers following
taxon initials are sample numbers and clone numbers ( if any) . Bootstrap percentages >50% are shown above the branches
422 植 物 分 类 与 资 源 学 报 第 36卷
Fig 3 Maximum parsimony tree inferred from atpB ̄rbcL sequences to show the relationships between the putative hybrids and putative parents.
Bootstrap percentages >50% are shown above the branches. Taxon initials and numbering are as in Fig 2
researchers and our field observation for years. They
flower in late June to Augustꎬ but their flowering
times differ somewhat: the anthesis L vellerea is a little
earlier than L subspicata.
Our ITS4 ̄5 data definitely support the hypothesis
that the morphologically intermediate individuals are
the progeny of hybridization between L vellerea and
L subspicata. According to the results of cpDNA analy ̄
sisꎬ we can also conclude that the hybridization is uni ̄
directional in the form of L subspicata♀× L vellerea .
Three types of putative hybrids were assigned
according to their different morphology. We thought
this hybridization might bidirectional and parental
species might more than the putative two. All of hy ̄
brids we studied were more close to parental species
of L subspicata. But with some different morphologi ̄
cal characters in detailꎬ the first hybrids type H ̄a
had L vellerea florets component part with several
ray florets except tubular florets in one capitulumꎬ
H ̄b had hairs on stem and H ̄c had ray florets.
Though they had same plastid donorꎬ they might in ̄
herit different copies of nuclear genetic material
which leads to different phenotype. Another possibil ̄
ity is F2ꎬ Fns or backcross appeared and hybrid
swarm formed at this population. Because materials
were limited in the first collectionꎬ new and long
term observation was needed for further studying.
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Appendix: List of accessions of Ligularia included in the phylogenetic analysis of nuclear rDNA ITS and atpB ̄rbcL sequences.
GenBank numbers for all accessions are provided.
Accessionsꎬ GenBank No.
ITS: Ligularia platyglossaꎬ AY458841ꎻ L stenoglossaꎬ AB523365ꎻ L japonicaꎬ AY458825ꎻ L atroviolaceaꎬ DQ272322ꎻ
L thyrsoideaꎬ DQ272320ꎻ L taquetiiꎬ GU323282ꎻ L kongkalingensisꎬ DQ272343ꎻ L curvisquamaꎬ DQ272324ꎻ L cyathicepsꎬ
DQ272328ꎻ L latihastataꎬ DQ272334.
atpB ̄rbcL: L franchetianaꎬ AB375447ꎻ L oligonemaꎬ AB523847ꎻ L anoleucaꎬ AB557885ꎻ L veitchianaꎬ AB557887ꎻ
Ligularia kanaitzensis var. subnudicaulisꎬ AB281495.
622 植 物 分 类 与 资 源 学 报 第 36卷