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Using Modified FIASCO Protocol to Isolate Polymorphic Microsatellite Loci in Chinese Brake Fern (Pteris vittata L.):an Arsenic-Hyperaccumulating Plant

改良FIASCO方法筛选砷超富集植物蜈蚣草SSR分子标记



全 文 :植物科学学报  2014ꎬ 32(4): 413~420
Plant Science Journal
    DOI: 10􀆰 3724 / SP􀆰 J􀆰 1142􀆰 2014􀆰 40413
改良FIASCO方法筛选砷超富集植物蜈蚣草SSR分子标记
李 磊1ꎬ 敖日格乐1ꎬ 王玢琪1ꎬ 葛台明1ꎬ2∗
(1. 中国地质大学湿地演化与生态恢复湖北省重点实验室ꎬ 武汉 430074ꎻ 2. 中国地质大学(武汉)环境学院ꎬ 武汉 430074)
摘  要: 蜈蚣草(Pteris vittata L.)是目前用于砷污染土壤修复最好的超富集植物ꎬ 但其分子水平上的研究数据较
少ꎮ 为了开发蜈蚣草特异性 SSR遗传标记ꎬ 本文采用改良的 FIASCO 方法从蜈蚣草 AG 和 AC 微卫星富集文库
中随机挑选 100个克隆ꎬ 分离得到 51 个微卫星位点ꎬ 其中 60%为完美型(Perfect)SSRꎮ 根据这些位点设计、
合成了 25对引物ꎬ 并对江西庐山及湖北恩施两地蜈蚣草种群各 20 个个体进行了遗传多样性检测ꎬ 结果发现:
其中 8个完美型及 1 个间断型( intermittent)SSR 位点的引物能够扩增出清晰、 稳定且具有多态性的条带ꎮ 9 对
引物共扩增出 41个等位基因ꎬ 各位点等位基因数在 2 ~ 7 之间ꎬ 平均等位基因数为 4􀆰 56 个ꎻ 期望杂合度在
0􀆰 0494 ~ 0􀆰 8169之间ꎻ 没有连锁不平衡现象发生ꎮ 采用大叶井栏边草(Pteris multifida Poir.)进行跨种扩增ꎬ
结果发现其中 6对引物能够进行种间扩增ꎮ 这些 SSR分子标记的开发有助于蜈蚣草生态适应性进化分析、 揭示
蜈蚣草地理分布格局以及探讨蜈蚣草遗传多样性ꎬ 还可用于品种鉴定及选育等ꎮ
关键词: 蜈蚣草ꎻ 微卫星ꎻ 多态性ꎻ FIASCOꎻ CviQI接头ꎻ pig ̄tail CviQI ̄N引物
中图分类号: Q75          文献标识码: A          文章编号: 2095 ̄0837(2014)04 ̄0413 ̄08
      收稿日期: 2013 ̄07 ̄09ꎬ 退修日期: 2013 ̄11 ̄13ꎮ
  基金项目: 国家自然科学基金重点项目(40930210)ꎮ
  作者简介: 李磊(1986- )ꎬ 男ꎬ 硕士研究生ꎬ 研究方向为分子生态学 (E ̄mail: 403218841@qq􀆰 com)ꎮ
  ∗通讯作者(Author for correspondence􀆰 E ̄mail: getaiming@cug􀆰 edu􀆰 cn)ꎮ
Using Modified FIASCO Protocol to Isolate Polymorphic
Microsatellite Loci in Chinese Brake Fern (Pteris vittata L􀆰 ):
an Arsenic ̄Hyperaccumulating Plant
LI Lei1ꎬ BAO Origil1ꎬ WANG Bin ̄Qi1ꎬ GE Tai ̄Ming1ꎬ2∗
(1. Hubei Key Laboratory of Wetland Evolution and Ecological Restorationꎬ China University of Geosciencesꎬ
Wuhan 430074ꎬ Chinaꎻ 2. School of Environmental Studiesꎬ China University of Geosciencesꎬ Wuhan 430074ꎬ China)
Abstract: Chinese brake fern (Pteris vittata L.) is the most important and well ̄known arsenic ̄
hyperaccumulating plant used in phytoremediation of arsenic contaminated soilsꎻ howeverꎬ
little is known about its genetic diversity. In this studyꎬ 100 clones were randomly selected from
the library enriched for AG and AC motifs using a modified FIASCO (Fast Isolation by AFLP of
Sequences Containing Repeats) protocol and sequenced. Fifty ̄one microsatellite lociꎬ of
which 60% were pure repeatsꎬ were isolated. Twenty ̄five pairs of primers were designed and
synthesized to evaluate their application and polymorphism in 20 individuals per sampling site
obtained from Lushan and Enshiꎬ respectively. Primers of eight loci of pure repeats and one
locus of intermittent repeats were finally amplified successfully and yielded clear bands. A total
of 41 alleles were detected. The allele number per locus of these microsatellites ranged from
two to seven (mean 4􀆰 56) . The expected heterozygosity (Exp ̄Het) ranged from 0􀆰 0494 to
0􀆰 8169. No linkage disequilibrium was found. Cross ̄species amplification demonstrated that
six loci were amplified successfully in P. multifida. The markers helped to reveal the genetic
variations of arsenic tolerant genotypes and understand the distribution pattern and ecological
adaptation mechanism of P. vittataꎬ and also assisted in breeding new varieties of fern for
more effective remediation.
Key words: Chinese brake fern (Pteris vittata L.)ꎻ Microsatelliteꎻ Polymorphismꎻ FIASCOꎻ
CviQI ̄adaptorꎻ Pig ̄tail CviQI ̄N primer
    In recent yearsꎬ arsenic pollution has be ̄
come a worldwide problem affecting human
health due to intense distortion caused by carci ̄
nogenic toxicity. Howeverꎬ the chemical form of
arsenic in soil and groundwater varies widelyꎬ
and governance is difficult. According to the
World Health Organizationꎬ at least 50 million
people worldwide have faced the threat of arse ̄
nic contamination. Arsenic pollution from manu ̄
facturingꎬ miningꎬ fertilizers and pesticides has
resulted in China becoming one of the most pollu ̄
ted countriesꎬ with Inner Mongoliaꎬ Guizhouꎬ Hu ̄
nanꎬ Sichuan and other provinces experiencing
particularly serious contamination. Currentlyꎬ the
traditional methods of repairing arsenic ̄contami ̄
nated soil are technically difficult and costlyꎬ
while phytoremediation based on hyperaccumula ̄
torsꎬ as first proposed by Brooks[1] in 1998ꎬ has
attracted growing attention due to its low cost
and environmental friendliness. A hyperaccumu ̄
lator has the capacity to absorb heavy metal 100
times more than that of a typical plant. Chinese
brake fern (Pteris vittata L.) was the first identi ̄
fied arsenic hyperaccumulator by Ma et al.[2]
and Chen et al.[3] simultaneously. Currentlyꎬ over
10 species of arsenic hyperaccumulators have
been found in the worldꎬ which are capable of
removing arsenic pollution from soil and ground ̄
water.
Chinese brake fern is widely distributed in
middle east and south China. It is traditionally cul ̄
tivated in gardensꎬ and is also used as an indica ̄
tor of calcareous soil. Since arsenic pollution in
soil has become a serious environmental and
health problem worldwideꎬ Chinese brake fern
has attracted increasing interest not only because
it is the first identified arsenic hyperaccumulatorꎬ
but also because it is one of the most effective ar ̄
senic hyperaccumulators for use in phytoreme ̄
diation of arsenic contaminated soils[2ꎬ3] . Accor ̄
ding to Chen et al.[3]ꎬ Chinese brake fern in Hu ̄
nan province efficiently extracted arsenic from
soils and translocated it to its frondsꎬ where arse ̄
nic concentrations reached 5070 mg / kg. Their
experiment showed that Pteris vittata L. reduced
total arsenic in the soil by 5% to 24% in one yearꎬ
which was 200 times greater than that of a typical
plant. As an arsenic hyperaccumulatorꎬ not only
does P. vittata L. exhibit strong resistance to ar ̄
senic and high arsenic enrichment capabilityꎬ but
it also has the characteristics of fast growthꎬ
large biomassꎬ and wide distributionꎬ indicating
that it is a very promising application plant. In the
past few yearsꎬ research on remediation efficien ̄
cy[4] and the mechanisms of arsenic detoxifica ̄
tion[5]ꎬ distribution[6] and hyperaccumulation[7]
have been developed. The morphology of Chi ̄
nese brake fern varies greatly. Furthermoreꎬ fin ̄
dings from other studies have shown that arsenic
accumulation level is positively correlated with
frond and spore number as well as plant
height[8]ꎬ indicating that ecotype (or genotype)
may be a key factor in arsenic accumulation.
Howeverꎬ little is known about the genetic diversi ̄
ty of this species.
Microsatellitesꎬ or simple sequence repeats
(SSR)ꎬ has been proved to be a useful marker
for studies on population geneticsꎬ molecular
phylogeography and genetic resources assess ̄
mentꎬ conservation and management due to their
co ̄dominanceꎬ high mutation rate and ease of
scoring[9] . In this senseꎬ SSR markers provide a
414 植 物 科 学 学 报 第 32卷 
powerful tool for investigating genetic diversityꎬ
identifying genotypes or ecotypesꎬ and breeding
new varieties of Chinese brake fern for more ef ̄
fective remediation. Thereforeꎬ it is necessary to
develop sufficient microsatellite markers with high
polymorphism for this valuable species. In this
studyꎬ we investigated the isolation of polymor ̄
phic microsatellite loci and their characterizations
in Chinese brake fernꎬ and examined the poten ̄
tial applicability of these DNA loci in Pteris multi ̄
fida Poir.ꎬ another potential phytoremediation
plant[10] from China.
1  Materials and Methods
1􀆰 1  Sampling and DNA extraction
Specimens of Chinese brake fern were col ̄
lected from Lushan National Park (29°34′21″Nꎬ
115°58′24″E) of Jiangxi province and Enshi city
(30°16′13″Nꎬ 109°28′30″E) of Hubei provinceꎬ
China ( 20 individuals per sampling site) . Ge ̄
nomic DNA was extracted using Cetyltrimethy ̄
lammonium bromide (CTAB) combined with iso ̄
propanol precipitation[11] .
1􀆰 2  Isolation of microsatellite markers
One Pteris vittata L. sample collected from
Enshi city (30°16′13″Nꎬ 109°28′30″E) was se ̄
lected to isolate polymorphic microsatellite loci
based on the modified FIASCO[9] . The DNA was
digested with CviQI (NEB) and ligated to CviQI ̄
adaptors ( 5′ ̄TAGTCAGGACTCAT ̄3′ / 5′ ̄GACGAT ̄
GAGTCCTGAC ̄3′) simultaneously in a total volu ̄
me of 25 μL containing 250 ng of genomic DNAꎬ
1 ×OnePhorAll bufferꎬ 5􀆰 0 mmol / L DTTꎬ 50 μg / mL
BSAꎬ 1􀆰 0 μmol / L adaptorꎬ 200 μmol / L ATPꎬ
2􀆰 5 U of CviQIꎬ and 1􀆰 0 U of T4 DNA ligase
(Promega) . The reaction was then incubated at
25℃ for 16 h. The digestion ̄ligation mixture was
diluted ( 1 ∶ 10) and the digested ̄ligated DNA
was further amplified using a pig ̄tail[12] CviQI ̄N
primer ( 5′ ̄GTTTATGAGTCCTGACTACN ̄3′) on
a Veriti® Thermal Cycler (Applied Biosystems) .
This PCR reaction was performed in a total volu ̄
me of 20 μL containing 1 × Taq reaction buffer
(Sangon Biotech Companyꎬ Shanghai)ꎬ 1􀆰 5 mmol / L
MgCl2ꎬ 2􀆰 5 μmol / L primerꎬ 200 μmol / L of each
dNTPsꎬ 0􀆰 5 U of Taq DNA polymerase (Sangon)ꎬ
and 5 μL of digested ̄ligated DNA dilution. The
PCR cycling conditions were: an initial denatur ̄
ation at 95℃ for 3 minꎬ followed by 14-26 cycles
of 94℃ for 30 sꎬ 53℃ for 30 sꎬ 72℃ for 30 sꎬ
and a final extension at 72℃ for 10 min. The PCR
conditions producing a clearly visible smear were
considered optimal and were selected for further
use. The purified PCR products (500 ng) were
hybridized to Biotin ̄labeled probes containing
repeat motifs (AC)12 and (AG)12 (100 μmol each)
in 100 μL hybridization solution (6 × SSC + 0􀆰 1%
SDS) at 48℃ for 90 min. Probe ̄bound DNA frag ̄
ments were then captured by streptavidin ̄coated
magnetic beads (Promega) at room temperature
for 30 min. Nonstringency washes and stringency
washes were performed as described in the
FIASCO protocolꎬ except the stringency eluent
was 0􀆰 5 × SSC + 0􀆰 1% SDS and the last strin ̄
gency wash was incubated for 5 min at 45℃ to
remove nonspecifically bound and unbound DNA.
Enriched DNA fragments were amplified with a
pig ̄tail CviQI ̄N primer under the conditions de ̄
scribed above. The purified PCR products were
ligated to pMD18 ̄T vector (TaKaRa) according
to the manufacturer􀆳s instructionsꎬ and then trans ̄
formed into Escherichia coli DH5α competent
cells. The positive clones were confirmed by co ̄
lony PCR using (AG / AC)12 and M13
+ / M13- as
primers[13]ꎬ and sequenced by the Sangon Bio ̄
tech Company (Shanghai) using an ABI PRISM
3730 sequencer (Applied Biosystems) . Microsa ̄
tellite sequences were screened using the soft ̄
ware SSRHunter 1􀆰 3[14] . Primer pairs for each mi ̄
crosatellite locus were designed with PrimerPre ̄
514  第 4期              李 磊等: 改良 FIASCO方法筛选砷超富集植物蜈蚣草 SSR分子标记(英文)
mier 5􀆰 0 software (http: / / www. premierbiosoft.
com / primerdesign / ) and synthesized by Sangon
Biotech Company (Shanghai) .
1􀆰 3  PCR amplification and genotyping
The microsatellite primers were then opti ̄
mized for annealing temperature and screened
for consistent amplification with 10 individuals.
PCR reactions were carried out in 10 μL total vo ̄
lumeꎬ which included 10 ng of genomic DNAꎬ
0􀆰 2 mmol / L of each dNTPsꎬ 0􀆰 2 μmol / L of each
primerꎬ 1 × PCR buffer ( Sangon)ꎬ 2 mmol / L
Mg2+ꎬ and 0􀆰 25 U of DNA Taq polymerase
(Sangon) . Amplification conditions were: 4 min
denaturation at 94℃ꎬ 35 cycles of 30 s at 94℃ꎬ
30 s at Ta (℃)ꎬ 30 s at 72℃ꎬ and a final exten ̄
sion of 72℃ for 10 min. Touch Down PCR was
performed for WGC ̄1ꎬ WGC ̄7 and WGC ̄14: an
initial denaturation at 94℃ for 5 minꎻ 10 cycles of
30 s at 94℃ꎬ 30 s at (Ta + 4)℃ꎬ and 20 s at
72℃ꎻ 30 cycles of 30 s at 92℃ꎬ 30 s at Ta (℃)
temperatureꎬ and 20 s at 72℃ꎬ and a final exten ̄
sion at 72℃ for 10 min. The amplification pro ̄
ducts were detected on 3% agarose gel.
Primers of eight loci of pure repeats and one
locus of near pure repeats (Table 1) were selected
to examine polymorphism in the 40 individuals col ̄
lected from Lushan National Park of Jiangxi pro ̄
vince and Enshi city of Hubei provinceꎬ China (20
individuals from each site). Amplified products were
separated on a 10% non ̄denaturing polyacrylamide
gel using silver staining. A 20 bp DNA ladder
(TaKaRa) was used to identify alleles.
Table 1  Characteristics of nine microsatellite loci for Pteris vittata tested on 40 individuals
(each population had 20 individuals)
Locus Repeatmotif Primer sequences (5′
- 3′) Size range(bp)
Ta
(°C) Na Ne
Obs ̄
Het
Exp ̄
Het Fis Fst GB Acc. No.
WGC ̄1 (TC)17
F: TTTTGTATTGGACACTGACACG
R: CGGACGGCATGGAGAAG 296
-348 54∗ 6 4􀆰 4024 0􀆰 0000 0􀆰 7832 1􀆰 0000 0􀆰 0164 KC698878
WGC ̄2 (AG)13
F: AGCCGCTTGAACAAAGTAAA
R: TACAAATTCCATTGAATGTGCT 136
-144 45 3 1􀆰 6134 0􀆰 2432 0􀆰 3854 0􀆰 3670 0􀆰 0040 KC698879
WGC ̄7 (TC)26
F: TCTCGTAGACCGATTTCCT
R: ACAGCCCACCTCTTTCC 102
-108 52∗ 4 2􀆰 2668 0􀆰 0000 0􀆰 5687 1􀆰 0000 0􀆰 4729 KC698884
WGC ̄10 (GA)18
F: CTCCCCTATAAGCGTTCAAGC
R: GCCCACATGGTCACCTCAA 100
-140 53 7 5􀆰 1429 0􀆰 2500 0􀆰 8169 0􀆰 6789 0􀆰 0339 KC698887
WGC ̄11 (CA)13
F: TCACCCTTGAACTCCCTC
R: TGAAGCCCTGCTATTGG 124
-126 55 2 1􀆰 0512 0􀆰 0000 0􀆰 0494 1􀆰 0000 0􀆰 0256 KC698888
WGC ̄13 (GA)14
F: TGCGTAAGCCAGCTCCACATC
R: GCCTCTATCTTCAGCGGGTTCAT 147
-167 55 6 4􀆰 1570 0􀆰 1333 0􀆰 7723 0􀆰 7849 0􀆰 1172 KC698890
WGC ̄14 (GA)23
F: AGTTGAAGGCTAAGGATGAT
R: GCACTATTCTAAATGGGTGA 179
-185 48∗ 4 3􀆰 5266 0􀆰 0323 0􀆰 7282 0􀆰 9532 0􀆰 0064 KC698891
WGC ̄22
(CT)8CC
(CT)14
F: ATGGCAGTAATGTTGCTATCTCCG
R: ATGGTGCATGTAAGGCTATTGGTT 226
-238 54 4 1􀆰 7455 0􀆰 2222 0􀆰 4331 0􀆰 4764 0􀆰 0063 KC698899
WGC ̄25 (CT)13
F: TCTATTGCTCTTACGCCCCTGAA
R: TTTGTGCCCATCCAACCTGA 176
-190 54 5 2􀆰 8851 0􀆰 3103 0􀆰 6649 0􀆰 5055 0􀆰 0407 KC698902
    Notes: Ta = Optimal annealing temperatures (℃)ꎻ Na = Observed number of allelesꎻ Ne = Effective number of allelesꎻ Observed
heterozygosity (Obs ̄Het) and expected heterozygosity (Exp ̄Het) were computed using Levene (1949)ꎻ Fis = Wright′s
(1978) fixation index (Fis) as a measure of heterozygote deficiency or excessꎻ Fst = F ̄statistics (Fst) as a measure of ge ̄
netic differentiation coefficientꎻ Accession number of GenBank (GB Acc. No.) . ∗: Touch Down PCR with 10 cycles of (Ta +
4)℃ꎬ followed by 30 cycles at Ta (℃) .
614 植 物 科 学 学 报 第 32卷 
1􀆰 4  Cross ̄species amplification
Pteris multifida is another plant that could be
potentially used in phytoremediation of arsenic
contaminated soils[10] . Specimens of P. multifida
Poir. were collected from the campus of the Chi ̄
na University of Geosciences (Wuhan) . Genomic
DNA was extracted using the CTAB method and
cross ̄species amplification was done under the
same PCR conditions used above.
1􀆰 5  Data analysis
The genotyping data were assessed for sco ̄
ring errors using MICRO ̄CHECKER 2􀆰2􀆰3[15] . All
diversity characteristics were calculated using
POPGENE V1􀆰31 software[16] . Tests for genotypic
linkage disequilibrium and Hardy ̄Weinberg equi ̄
librium (HWE) were also conducted using the
same software package.
2  Results
2􀆰 1   Digestionꎬ ligation and adaptor ̄mediated
amplification of genomic DNA
The genomic DNA was efficiently digested
by CviQI endonuclease and ligated to the CviQI ̄
adaptor simultaneously. The digested ̄ligated DNA
was successfully amplified using a pig ̄tail CviQI ̄
N primerꎬ forming a clear smear of fragments
centered at approximately 500 bp ( Fig􀆰 1: A) .
The enriched DNA was also recovered by the
primer (Fig􀆰 1: B) successfully.
2􀆰 2  Distribution and characteristics of the micro ̄
satellites
We randomly selected 100 clones. Among
themꎬ 61 clones were confirmed positive by colo ̄
ny PCR (Fig􀆰 1: C) and sequenced. A total of 51
clones contained the target repeating sequen ̄
cesꎬ indicating that enrichment efficiency was as
high as 51% (51 / 100) . Among the repeating se ̄
quencesꎬ approximately 80% contained the AG /
CT motifꎬ only 4% contained the AC / GT motifꎬ
and the other sequences contained AG / CT and
A B C
D
A: Amplification after digestion ̄ligation (1􀆰 5% agarose gelꎬ
Marker: TaKaRa DL5000 )ꎻ B: PCR recovery of enriched
DNA ( 1􀆰 5% agarose gelꎬ Marker: TaKaRa DL5000)ꎻ C:
Identification of positive clones in the enriched library by colo ̄
ny PCR ( 3% agarose gelꎬ Marker: TaKaRa DL2000)ꎻ D:
Amplification of primer WGC ̄22 in 40 individuals (3% agarose
gelꎬ Marker: TaKaRa DL2000) .
Fig􀆰 1  Results of the modified FIASCO protocol
AC / GT compound motifsꎬ indicating that the AG
repeating sequence was much more abundant in
the genome of Chinese brake fern than that of
AC. Furthermoreꎬ 60% of the SSR ̄containing se ̄
quences had perfect repeats. Because perfect
repeats[17] are more suitable for population analy ̄
sisꎬ these results revealed that our modified FI ̄
ASCO method worked very well in Chinese brake
fern genome and exhibited very high specificity.
2􀆰 3  Primer design and polymorphism detection
Among the 51 microsatellite lociꎬ PrimerPre ̄
mier created putative primer sets for 25 loci
(GB Acc. No. KC698878 ̄KC698902) with scores
higher than 90 points. These primer sets were
considered as candidate pairs and synthesized.
Primers of eight loci of pure repeats and one lo ̄
cus of intermittent repeats (Table 1) yielded suc ̄
cessful amplicons of the expected size consist ̄
ently (Fig􀆰 1: D)ꎬ and were further examined for
polymorphism.
Polymorphisms were detected on 10% non ̄
denaturing polyacrylamide gel ( Fig􀆰 2 ) . The
number of alleles of the primers ranged from two
to seven. Furthermoreꎬ seven loci possessed more
714  第 4期              李 磊等: 改良 FIASCO方法筛选砷超富集植物蜈蚣草 SSR分子标记(英文)
AB
A: Amplification of primer WGC ̄10 (100-120 bp) in
LuShan population ( 20 individuals ) ( 10% PAGE
gelꎬ Marker: TaKaRa 20 bp DNA ladder. From top to
bottom: 200ꎬ 180ꎬ 160ꎬ 140ꎬ 120ꎬ 100 bp)ꎻ B:
Amplification of primer WGC ̄10 in EnShi population
(20 individuals) (10% PAGE gelꎬ Marker: TaKaRa
20 bp DNA ladder. From top to bottom: 200ꎬ 180ꎬ
160ꎬ 140ꎬ 120ꎬ 100 bp) .
Fig􀆰 2  Amplified results of primer WGC ̄10
than three alleles per locus. The effective num ̄
bers of alleles were between 1􀆰0512 and 5􀆰1429.
Obs ̄Het were 0 to 0􀆰 3103ꎬ while Exp ̄Het were
between 0􀆰0494 and 0􀆰 8169. We also tested the
coefficients for heterozygote deficiency (Fis) and
genetic differentiation coefficient ( Fst) . The Fis
were between 0􀆰 3670 and 1􀆰0000ꎬ while the Fst
were between 0􀆰 0040 and 0􀆰 4729 (Table 1) . No
significant linkage disequilibria were detected. All
loci deviated from the Hardy ̄Weinberg equilib ̄
rium (P < 0􀆰 05) .
2􀆰 4  Cross ̄species amplification
To examine the potential utility of these mic ̄
rosatellite markers developed for Chinese brake
fern in other Pteris speciesꎬ cross ̄species ampli ̄
fication was also conducted using genomic DNA
from 10 individuals of P. multifida ( Table 2) .
Primer sets of WGC ̄1 and WGC ̄7 amplified an
unstable band with a size similar to Chinese
brake fernꎬ while primer set of WGC ̄25 amplified
a very clear band (750 bp) that was much larger
than expected. Six of the nine loci amplified in
Chinese brake fern also amplified a band of simi ̄
lar size in P. multifida ( Table 2 ) . Thereforeꎬ
these loci might facilitate evolutionary and popu ̄
lation genetic studies as well as breeding and
cultivar development in P. multifida.
3  Discussion
The morphology of Chinese brake fern va ̄
ries greatly. The height ranges from 0􀆰 2 to 2 m.
It also has a great change in biomass ranging in
5 -36 t / hm2( fresh weight) [3] . Wei[18] suggested
that the uptake of arsenic had no relationship with
the ecotype of Pteris vittata L.ꎬ while other stu ̄
dies[8] showed that arsenic accumulation was
positively correlated with frond numberꎬ spore
number and plant heightꎬ which provides a rea ̄
listic basis as well as theoretical significance for
the development of SSR markers. At presentꎬ few
studies have been conducted on the genetic di ̄
versity of ferns[19] . Furthermoreꎬ genetic research
on species such as Pteris vittata L. is particularly
limited. Zhou[20] found a high degree of genetic
diversity in limestone areas in Guangxi Pteris
vittata L. populations using allozyme analysisꎬ but
the degree of difference was not proportional to
distance and space. Yang[21] collected Pteris vittata
L. samples from Guangzhou and Hunan province
and developed eight pairs of SSR primers. A pre ̄
liminary analysis of genetic diversity of the two
populations was conductedꎻ howeverꎬ the eight
Table 2  Amplification of nine microsatellite primers developed for Pteris vittata in P. multifida
Locus WGC ̄1 WGC ̄2 WGC ̄7 WGC ̄10 WGC ̄11 WGC ̄13 WGC ̄14 WGC ̄22 WGC ̄25
Result ± + ± + + + + + -
    Notes: ‘+’ denotes amplification of a band in the same size range as P. vittataꎬ ‘±’ denotes unstable amplificationꎬ and ‘-’ de ̄
notes no amplification in the same size range as P. vittata.
814 植 物 科 学 学 报 第 32卷 
pairs of primers were not particularly perfect.
In the present studyꎬ the construction of the
library enriched for (AG)n / (AC)n microsatellite
repeat sequences and primer exploitation of Pte ̄
ris vittata was based on a modified FIASCO pro ̄
tocol. Our data showed that the modifications
were successfulꎬ and both enrichment efficiency
and specificity were improved.
The GTTT “pig ̄tail” was first used in micro ̄
satellite isolation by Glenn and Schable[12] to en ̄
sure efficient A ̄tailing of each PCR productꎬ
which would yield good results from TA cloning.
We also found that the pig ̄tail CviQI ̄N primer
could improve the amplification efficiency com ̄
pared to that of normal CviQI ̄N primer (5′ ̄GAT ̄
GAGTCCTGACTACN ̄3′) (data not shown) . We
also found that the stringent eluent 0􀆰 5 × SSC +
0􀆰1% SDS used to remove nonspecifically bound
and unbound DNA performed better than that of
stringent eluent 0􀆰 2 × SSC + 0􀆰1% SDSꎬ and the
last stringent washing incubated at 45℃ꎬ which
was about 10℃ lower than the melting tempera ̄
ture of the probesꎬ was an appropriate stringent
washing strength to get the best elution efficien ̄
cy.
The high percentage (60%) of pure repea ̄
ting sequences indicated that the loci we en ̄
riched were more ideal than those enriched by
Yang[21] and also demonstrated that our modifi ̄
cations worked well with the FIASCO protocol.
The AG repeating sequence was much more a ̄
bundant in the Chinese brake fern genome than
that of ACꎬ which is consistent with the findings
of Yang[21] .
Howeverꎬ during the evaluation of these SSR
polymorphismsꎬ we found that all loci deviated
from the Hardy ̄Weinberg equilibrium (P < 0􀆰 05).
Although limited sample sizeꎬ null alleles and
geographical sites of the samples might result in
the deviationꎬ the more reasonable explanation
for the deviation is that most fernsꎬ including Chi ̄
nese brake fernꎬ reproduce by selfing. This is al ̄
so proved by the positive coefficients for hetero ̄
zygote deficiency (Fis)ꎬ which illustrated that the
loci were dominantly homozygous. We also tested
the degree of genetic differentiation between En ̄
shi and Lushan populations by Fstꎬ which ranged
from 0􀆰0040 to 0􀆰4729. This indicated that no
gene flow barrier existed between the two popu ̄
lations.
The highly conserved flanking sequences of
the SSR ensured the potential utility of these mic ̄
rosatellite markers developed for Chinese brake
fern in P. multifida Poir.ꎬ except that different
species had different amplification conditions. Six
of the nine loci amplified in Chinese brake fern al ̄
so amplified similar band(s) in P. multifidaꎬ re ̄
vealing that these loci can facilitate evolutionary
and population genetic studies as well as bree ̄
ding and cultivar development in P. multifida.
The new microsatellite markers developed in
this study will be useful for investigating genetic
diversityꎬ population structureꎬ and mating pat ̄
ternsꎬ for identifying varieties and ecotypesꎬ and
for hybrid selection in breeding program of Chi ̄
nese brake fern.
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914  第 4期              李 磊等: 改良 FIASCO方法筛选砷超富集植物蜈蚣草 SSR分子标记(英文)
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024 植 物 科 学 学 报 第 32卷