全 文 :书食用菌学报2014.21(2):1~8
收稿日期:2014-03-29原稿;2014-05-06修改稿
基金项目:上海市科委重点科技攻关项目(编号:10391900900)、种业发展专项[编号:沪农科种字(2012)第6号]、国
家科技支撑项目(编号:2013BAD16B02)、上海市农业科学院青年科技基金[编号:农青年科技2013(20)]
的部分研究内容
作者简介:张 丹(1986-),男,2011年毕业于扬州大学农学院作物遗传育种专业,硕士,研究实习员,主要从事食
用菌遗传育种研究。
*本文通讯作者 E-mail:S62209760@163.com
文章编号:1005-9873(2014)02-0001-08
基于全基因组序列的香菇商业菌种
SSR遗传多样性分析及多位点指纹图谱构建的研究
张 丹1,宋春艳1*,章炉军1,巫 萍1,2,鲍大鹏1,尚晓冬1,谭 琦1
(1上海市农业科学院食用菌研究所,农业部南方食用菌资源利用重点实验室,国家食用菌工程技术研究中心,
上海市农业遗传育种重点开放实验室,上海201403;2南京农业大学生命科学学院,江苏南京210095)
摘 要:香菇(Lentinula edodes)是世界主要栽培食用菌之一,香菇菌种的准确鉴定是香菇大规模生产和菌种
知识产权保护的重要前提。本研究基于香菇全基因组序列开发200对SSR标记用于25份常用香菇栽培菌种
的遗传多样性分析和菌种鉴定。结果表明:供试材料的遗传相似性较高,遗传相似系数平均值为0.776,最小
值为0.567,最大值为1。基于遗传多样性分析结果,筛选出7对带型清晰且重复性好的SSR标记,并成功构
建了11份香菇商业菌种的多位点SSR指纹图谱。这11份菌种分别为:Cr-02、闵丰1号、香菇241-4、森源1
号、森源8404、香九、广香51号、华香5号、L952、L9319、L808。
关键词:香菇;简单重复序列;商业菌种;遗传多样性;指纹图谱
香菇(Lentinula edodes)是我国十分重要的
栽培食用菌。自上世纪70年代以来,随着品种
改良以及代料栽培技术的推广,我国香菇总产量
有了极大的提高,逐渐占到世界总产量的70%以
上[1]。据中国食用菌协会统计,2012年我国香菇
总 产 量 达 到 400 万 吨,仅 次 于 糙 皮 侧 耳
(Pleurotus ostreatus),是我国第二大栽培食用
菌。随着香菇栽培规模的逐步扩大,香菇栽培菌
种的使用数量也越来越多,目前已有25份香菇
菌种通过了国家品种审定委员会的认定,用于大
规模的商业生产。
对于香菇产业来说,优质的菌种对香菇产量
和质量的贡献至关重要。目前,我国的香菇栽培
正逐步从分散的小农小户生产向着专业化、分工
化、规模化的方向发展,对香菇栽培菌种的质量
和真实性要求越来越严格。由于缺乏简洁高效
的菌种检测手段,生产上假菌种、退化菌种时常
冒充优良商业菌种流通于市场,导致菌种供应者
和香菇生产者遭受巨大经济损失,迫切需要研制
简便、快速、准确的菌种鉴定技术,以保证生产用
种的准确无误。
菌种的真实性常通过基于表型分析的 DUS
(Distinctness,Uniformity and Stability)测试来
鉴定。这种方法耗时费力,鉴定结果也易受环
境的干扰。近年来,随着分子生物学技术的发
展,越来越多的分子标记,如 RAPD (Radom
Amplified Polymorphic DNA )
[2]、 AFLP
(Amplified Fragment Length Polymor-
phism )
[3]、ISSR (Inter Simple Sequence
Repeats)
[4]以及SCAR(Sequence Characterized
Amplified Region)
[5-7]相继被应用于菌种真实性
鉴定的研究。分子标记以其快速、简便、可操作
性强等优点得到了迅速的推广。然而,在实际
应用中,上述分子标记也体现出一些缺点,例如
RAPD、AFLP以及ISSR 标记扩增出的条带数
量较多,统计分析比较繁琐且部分标记的可重
复性较低[8];SCAR标记由于受基因组序列信息
的限制,目前可利用的标记数量较少。这些缺
点限制了上述分子标记的使用范围和检测
效率。
随着全基因组测序技术的不断发展,国内
外研究者开发了大量的新一代分子标记,如
食 用 菌 学 报 第21卷
SSR(Simple Sequence Repeat)、SNP(Single
Nucleotide Polymorphism)等,这些标记被越来
越多地应用于遗传学研究。其中,SSR标记具
有数量多、多态性高、共显性、易操作等优点。
在植物上 SSR 标记早已用于品种的鉴定研
究[9-12]。在食用菌领域,当全基因组尚未测序
时,研究者常利用表达序列标签(EST)数据
库[13]或 是 采 用 FIASCO (Fast Isolation by
AFLP of Sequences Containing Repeats)方法
[14]
以及ISSR-抑制PCR法[15]开发了少量SSR标
记。随着香菇全基因组序列测序工作的完成,
基于全基因组数据库开发大量遍布全基因组的
SSR标记已成为现实。
笔者在香菇菌种L135全基因组测序完成
的基础上,拟初步开发200对SSR标记,并对25
份经国审认定的香菇商业菌种进行SSR基因型
鉴定。一方面检测所开发SSR标记的实用性;
另一方面可考察现有商业菌种的遗传多样性。
此外,基于菌种的遗传多样性分析,还拟构建多
位点SSR指纹图谱,用于鉴定常用的香菇商业
菌种,以期推动香菇菌种真实性鉴定技术的
发展。
1 材料与方法
1.1供试菌种
25份经国家品种审定委员会认定的香菇(L.
edodes)商业栽培菌种,保藏于国家食用菌标准菌
种 库 (China Center for Mushroom Spawn
Standards and Control,CCMSSC),详见表1。
1.2供试培养基
斜面固体培养基(PDA):200g马铃薯、20g
葡萄糖、20g琼脂、1000mL水,pH自然。
液体培养基:200g马铃薯、20g葡萄糖、
1000mL水,pH自然。
1.3菌丝DNA提取
4~5块米粒大小PDA斜面活化菌种块接入
装100mL液体培养基的250mL三角瓶中,每
个菌株2瓶,置于140r/min摇床上,25℃恒温
培养7d。滤纸过滤收集菌丝,蒸馏水冲洗,滤纸
吸干后,称取1g。采用 CTAB法提取基因组
DNA[2,16]。使用分光光度计(NanoDrop-1000,
Thermo公司,USA)对提取的DNA进行浓度和
纯度检测。分别将提取的 DNA 溶液稀释至
50ng/μL,4℃保存备用。
1.4SSR标记的开发
基于香菇全基因组数据库,利用Perl软件运
行 MISA 脚 本 程 序[17]结 合 Primer Premier
3.0[18]软件初步设计了200对SSR引物,并委托
上海生工生物工程公司合成。
表1 供试香菇商业栽培菌种
Table 1 Commercial cultivars of L.edodes
included in test study
菌株编号
Cultivar name
认定编号
Identified no.
菌种来源
Source
申香8号Shen-8 2007001
申香10号Shen-10 2007002
申香12号Shen-12 2007003
上海
Shanghai
Cr02 2007004
L135 2007005
闵丰1号 Minfeng-1 2007006
Cr62 2007007
Cr04 2007008
福建省
Fujian
Province
庆元9015Qingyuan9015 2007009
香菇241-4Xianggu241-4 2007010
武香1号 Wuxiang-1 2007011
赣香1号 Ganxiang-1 2007012
菌兴8号Junxing-8 2008007
L9319 2008008
L808 2008009
浙江省
Zhejiang
Province
金地香菇Jindi 2007013
四川省
Sichuan
Province
森源1号Senyuan-1 2007014
森源10号Senyuan-10 2007015
森源8404Senyuan8404 2007016
华香8号 Huaxiang-8 2008004
华香5号 Huaxiang-5 2008005
L952 2008006
湖北省
Hubei
Province
香九 Xiang-9 2008001
香杂26Xiangza-26 2008002
广香51号Guangxiang-51 2008003
广东省
Guangdong
Province
1.5SSR基因型鉴定
PCR 反 应 所 使 用 PCR 仪 为 Mycycler
thermal cycler(Bio-Rad公司,USA),反应体系
为20μL,包括:2μL 10 × Reaction buffer
(Promega,不含 Mg2+),2μL MgCl2(Promega,
25 mmol/L),0.4μL dNTP (10mmol/L),
0.2μL Taq 聚合酶 (5U/μL,Promega公司产
品),2μL模板DNA(50ng/μL),正向和反向引物
各1μL(10μmol/L),以及11.4μL ddH2O。
2
第2期 张 丹,等:基于全基因组序列的香菇商业菌种SSR遗传多样性分析及多位点指纹图谱构建的研究
PCR反应采用Touchdown程序[19],参数设
置如下:95 ℃ 预变性5min,95 ℃变性30s,
67℃退火50s,72℃延伸30s,2次循环;退火温
度以2℃的梯度逐渐降至51℃,每个退火温度
均扩增2循环;95℃变性30s,退火温度55℃退
火50s,72℃延伸30s,连续扩增25循环;最后保
持72℃延伸7min。
PCR扩增反应完成后,PCR产物的变性、电
泳以及银染拍照同文献[20]。
1.6数据分析
扩增产物的条带记录方式为:同一个SSR标
记扩增出的等位差异片段,相同迁移率的位置有
条带的记录为“1”,没有条带的记录为“0”。
SSR标记的多态性分析采用PowerMarker
3.0 软 件[21] 计 算 多 态 性 信 息 量 (PIC,
polymorphism information content)。 利 用
NTsys2.10软件[22]对香菇商业菌种进行遗传多
样性分析,根据Nei’s遗传距离计算菌株间的遗
传相似系数,根据非加权组平均法(UPGMA)对
菌种进行系统聚类分析。
筛选退火温度相同的SSR引物用于构建指
纹图谱,经3次重复扩增,记录等位差异片段数
量变化范围和片段分子量大小。选取条带清晰
稳定的等位差异片段,根据分子量从大到小,依
次编码,根据编码组合的差异分析区分鉴定不同
的菌种。
2 结果与分析
2.1SSR标记的多态性分析
25份供试材料的PCR扩增结果表明,设计
的200对SSR标记中有110对标记得到了扩增
产物,其中扩增产物表现出多态性的标记有98
对,占所开发标记的49%。98对多态SSR标记
共扩增出545个条带,单个SSR标记扩增出的等
位差异片段个数的变化范围为2~12。98对多
态SSR 标记的平均 PIC 值(多态信息量)为
0.458,最大值为0.863,最小值为0.077。
2.2供试材料的遗传多样性分析
根据98对多态SSR标记在供试材料上扩增
的基因型数据,对25份香菇商业菌种进行了遗
传多样性分析。结果表明,供试材料的遗传相似
性系数平均值为0.776,最大值为1,最小值为
0.567。在遗传相似系数为0.73时可将25份香
菇商业菌种分为3大类(图1)。第一类包含了:
图1 基于SSR标记的25份香菇商业菌种的UPGMA系统聚类图
Fig.1 UPGMA dendrogram of 25commercial L.edodes cultivars based on SSR markers
3
食 用 菌 学 报 第21卷
申香8号、申香10号、申香12号、香杂26、武香1
号、Cr04、菌兴8号、Cr62、赣香1号、华香8号、
闵丰1号、L9319、Cr02、森源1号、华香5号、
L808、L952等17份材料;第二类包含了:庆元
9015、金地香菇、香菇241-4、森源8404、L135、森
源10号、广香51号等7份菌株;第三类仅包含香
九1份菌种。SSR标记的遗传多样性分析结果
还表明现有商业菌种相当一部分材料之间遗传
背景的相似性非常高。申香8号、申香10号、申
香12号、香杂26、武香1号、Cr04、菌兴8号间的
遗传相似系数的平均值达到0.998。香菇241-4
和森源8404间的遗传相似系数达到0.991。
Cr62、赣香1号和华香8号之间,庆元9015和金
地香菇之间以及L135和森源10号之间的遗传
相似系数分别均为1。
2.3供试材料的多位点SSR分子表型分析
在遗传相似系数为0.99时,可以将供试香
菇商业菌种分为15个在遗传上具有差异的类
群。能够区分鉴定这15个类群的7对SSR标记
见表2。单个标记扩增的等位差异片段数量变化
范围为2~5个,片段分子量大小分布于260~
930bp之间。
选取其中20个条带清晰稳定、重复性好的
等位差异片段,通过人工读数和编码分别记录
了所有供试材料的7位点SSR分子表型数据
(表3),这些分子表型数据是构建供试香菇商业
菌种SSR指纹图谱的基础。表2中记录了7对
SSR标记所扩增等位差异片段的数量及其相对
于标准50bp DNA ladder标记的分子量,表3
是所有供试香菇商业菌株的7位点SSR分子表
型数据。通过表2中的编码转换,供试菌种分
子表型的差异性分析可通过简单的描述性统计
分析快速实现,该方法在大规模数据分析时将
非常高效。
表2 用于构建指纹图谱的7对SSR标记及其等位差异片段信息
Table 2 Fragments amplified by seven primer pairs selected to construct fingerprint profiles
标记名称
Primer pair
重复序列
Repeat sequence
正向/反向引物(5’→3’)
Forward/Reverse primer(5’→3’)
等位差异片段编码
Fragments
片段大小
Fragments size(bp)
Le_fp01 (CT)7
ACGCGTATCCTCCCCTAAGT/
AAGCGATATGGATTTGACGC
1
2
600
530
Le_fp02 (CGAC)6
GGGCGAAACAATTTCAGGTA/
ATGCCATCGTAAGGAACTCG
1 290
2 280
3 270
4 260
Le_fp03 (CT)9
ATTGTGACTCGACCACCTCC/
TCATAATGCATCCCGTGAGA
1 900
2 800
Le_fp04 (AGGT)5
CCCAAAAAGGATTTCAGCAA/
AACCGGAGTGGTGTAAGTGC
1 400
2 390
Le_fp05
(TAC)
7tatgtaga(GGAT)6
CATCAACCAAACCAAGATTCAA/
TTCCAATTTCCTCCGAGTCA
1 930
2 850
3 760
4 700
5 530
Le_fp06 (TCA)6
CATGGGAGAGATTCGGAAAA/
CGAGACCGACGACTTTGACT
1 800
2 780
Le_fp07 (CTC)6
CATTGCTCGGATCCTTCATT/
TACCTCGTGCGGACTTTGAT
1 700
2 600
4
第2期 张 丹,等:基于全基因组序列的香菇商业菌种SSR遗传多样性分析及多位点指纹图谱构建的研究
经过统计分析发现,这7对SSR标记在25
份香菇商业菌种上共产生15种分子表型。其中
11份商业菌种具有各自特异的分子表型,这些菌
株分别为:Cr-02、闵丰1号、香菇241-4、森源1
号、森源8404、香九、广香51号、华香 5 号、
L952、L9319和L808。剩余的14份商业菌种具
有4种分子表型,其中(A)申香8号、申香10号、
申香12号、Cr-04、菌兴8号、武香1号和香杂26
具有同一种分子表型;(B)Cr-62、赣香1号和华
香8号具有同一种分子表型;(C)L135和森源
10号具有同一种分子表型;(D)庆元9015和金
地香菇具有同一种分子表型。
表3 25份香菇商业菌种的7位点SSR分子表型
Table 3 Molecular phenotypes characterized by different combinations of numbered fragments amplified from 25
L.edodes cultivars using seven SSR primer pairs
菌株名称
Cultivar name
引物Primer pair
Le_fp01 Le_fp02 Le_fp03 Le_fp04 Le_fp05 Le_fp06 Le_fp07
申香8号Shen-8 1,2 1,4 1,2 1,2 3 1,2 1,2
申香10号Shen-10 1,2 1,4 1,2 1,2 3 1,2 1,2
申香12号Shen-12 1,2 1,4 1,2 1,2 3 1,2 1,2
Cr04 1,2 1,4 1,2 1,2 3 1,2 1,2
武香1号 Wuxiang-1
香杂26Xiangza-26
1,2
1,2
1,4
1,4
1,2
1,2
1,2
1,2
3
3
1,2
1,2
1,2
1,2
菌兴8号Junxing-8 1,2 1,4 1,2 1,2 3 1,2 1,2
Cr62 1 1,4 1,2 1,2 3 1,2 1,2
赣香1号 Ganxiang-1 1 1,4 1,2 1,2 3 1,2 1,2
华香8号 Huaxiang-8 1 1,4 1,2 1,2 3 1,2 1,2
庆元9015Qingyuan9015 1 1,4 1 1 4,5 1,2 2
金地香菇Jindi 1 1,4 1 1 4,5 1,2 2
L135 2 1 1 1 2,5 2 1,2
森源10号Senyuan-10 2 1 1 1 2,5 2 1,2
Cr02 1 1,2 1,2 2 3 1,2 1
闵丰1号 Minfeng-1 1,2 1,4 1,2 2 3 2 2
香菇241-4Xianggu241-4 1 3,4 1 1 1,3 2 2
森源1号Senyuan-1 1 2,4 1 1 3 1,2 1,2
森源8404Senyuan8404 1,2 3,4 1 1 1 2 2
香九 Xiang-9 1 3 1 - 5 2 1
广香51号 Guangxiang-51 1,2 1,3 1 - 2,5 2 1,2
华香5号 Huaxiang-5 1 1,4 1 1,2 4 2 1
L952 1 1,4 1 2 4,5 2 1
L9319 1 1 1,2 1 3 1,2 1,2
L808 1,2 4 1 2 4,5 2 1
“-”表示没有扩增出条带 “-”indicates an absence of amplification products
2.4构建11份国审香菇商业菌种的SSR指纹
图谱
基于25份香菇商业菌种的7位点SSR分子
表型,构建了11份具有特异分子表型的香菇菌
种的多位点SSR指纹图谱,部分代表图谱见图
2。由于所筛选的SSR引物具有相同的退火温
度,11份菌种的指纹图谱通过一次PCR反应可
全部完成。
5
食 用 菌 学 报 第21卷
泳道M:标准分子量标记(GeneRulerTM 50bp DNA ladder plus);泳道1-7:表2中的SSR引物;泳道C:空白对照;用于构建指纹图谱的
SSR等位差异片段均用黑色箭头标识
Lane M:molecular marker(GeneRulerTM 50bp DNA ladder plus);Lanes 1-7,amplification products using SSR primers listed in
Table 2;Lane C,control;Numbers on the left of each figure indicate the DNA size markers in base pairs(bp);Fragments used to
construct fingerprint profiles are indicated by black arrows
图2 部分香菇商业菌种的多位点SSR指纹图谱
Fig.2 Multilocus SSR fingerprint profiles of three commercial L.edodes cultivars
3 讨论
香菇菌种作为基础生产资料,是香菇商业生
产体系里最重要的一个因素。在固定生产程序
下,香菇菌种的质量直接决定着香菇子实体的产
量和品质。因此,对商业菌种进行真实性鉴定有
助于香菇产业的健康发展。如何建立高效稳定
的菌种真实性鉴定方法正成为近年来的研究热
点之一。
作为一种数量多、多态性高且共显性的分子
标记,SSR标记在遗传多样性分析、遗传连锁图
谱构建以及分子进化等领域具有十分广泛的应
用[23-26]。随着基因组测序技术的不断发展,大型
真菌中越来越多的研究者开始对SSR标记进行
开发和利用。例如,双色蜡蘑(Laccaria bicolor)
基因组上检测到了277062个SSR位点,其占整
个基 因 组 序 列 的 比 例 达 到 8%[17,27]。灵 芝
(Ganoderma lucidum)全基因组SSR位点的数
目初步检测为1206~6104个,占整个基因组的
比例为0.04%~0.15%[28]。在SSR标记的应用
方面,利用FIASCO程序开发的17对SSR标记
可对16个黑木耳(Auricularia auricula-judae)
栽培菌种进行区分鉴定[14]。双孢蘑菇(Agaricus
bisporus)上,利用3对多态SSR标记即可将28
个菌株中的27个进行区分鉴定[29]。这些研究均
表明,SSR标记在菌种鉴定方面具有较大的应用
潜力。
笔者基于香菇菌株L135全基因组序列初步
开发了200对SSR标记,通过对25份国审香菇
商业菌种的遗传多样性分析,成功筛选7对条带
清晰稳定、重复性好且退火温度一致的SSR标
记,适用于香菇菌种的鉴定。研究结果表明,在
25份国审香菇菌种中有11份菌种可被区分鉴
定,剩余14份菌种可被分为4类。
基于菌种的SSR分子表型,构建了11份香
菇商业菌种的多位点SSR指纹图谱。相比于已
有的RAPD,ISSR以及SCAR等标记建立的香
菇指纹图谱[2,4-6],SSR指纹图谱具有条带清晰易
读、稳定性好等优点。
随着食用菌产业的不断发展,越来越多的菌
种将流通于市场,菌种真实性鉴定也必将广泛推
广。伴随着食用菌基因组测序工作的开展,分布
于全基因组的大量SSR标记将会被开发和利用。
本研究结果表明,基于全基因组序列开发的SSR
标记在香菇菌种遗传多样性分析以及菌种鉴定
等方面具有重要的应用价值。由于所选供试香
菇商业菌种的遗传多样性较低,试验所利用的
SSR标记数量有限,尚有一部分菌种的遗传特异
性无法鉴定。后续研究将基于香菇全基因组序
列开发更多的SSR分子标记,同时结合其他可利
用的分子标记来构建所有香菇栽培菌种的指纹
图谱。
参考文献
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early cultivation of Letinus in China[J].Mushroom
6
第2期 张 丹,等:基于全基因组序列的香菇商业菌种SSR遗传多样性分析及多位点指纹图谱构建的研究
J Trop,1987,7:31-37.
[2]ZHANG Y, MOLINA FI. Strain typing of
Lentinula edodes by random amplified polymorphic
DNA assay[J].FEMS Microbiol Lett,1995,131
(1):17-20.
[3]LO TC,KANG MW,WANG BC,et al.Glycosyl
linkage characteristics and classifications of exo-
polysaccharides of some regionaly different strains
of Lentinula edodes by amplified fragment length
polymorphism assay and cluster analysis[J].Anal
Chim Acta,2007,592(2):146-153.
[4]ZHANG RY,HUANG CY,ZHENG SY,et al.
Strain-typing of Lentinula edodes in China with
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61(5):381-389.
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Microbiol Biotechnol,2008,81(2):303-309.
[7]QIN LH,TAN Q,CHEN MJ,et al.Use of
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[J].FEMS Microbiol Lett,2006,257(1):112-116.
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the use of SCAR markers for screening genetic
diversity of Lentinula edodes strains[J].Curr
Microbiol,2012,64(4):317-325.
[9]DELGADO - MARTINEZ FJ, AMAYA I,
SANCHEZ-SEVILLA JF,et al. Microsatelite
marker-based identification and genetic relationships
of olive cultivars from the Extremadura region of
Spain[J].Genet Mol Res,2012,11(2):918-932.
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based DNA fingerprinting and cultivar
identification of olives (Olea europaea)[J].
Biochem Genet,2011,49(9-10):555-561.
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var.bisporusx×A.bisporus var.burnetti hybrid
based on AFLP,SSR and CAPS markers sheds
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[24]LABBE J,ZHANG X,YIN T,et al.A genetic
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Laccaria bicolor genome [J]. J Microbiol
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[本文编辑] 于荣利
8
ACTA EDULIS FUNGI2014.21(2):9~13
Received:March 29,2014; Accepted:May 6,2014
Sponsored by Shanghai Science and Technology Office (No.10391900900,Foundation of Seed Industry
Development(No.2012-6SAAS),National Science and Technique Foundation (No.2013BAD16b02),the
Foundation of Shanghai Academy of Agricultural Sciences[No.2013(20)]
*Corresponding author. E-mail:S62209760@163.com
Genetic Diversityand Fingerprint Profiles of
Commercial Lentinula edodes Cultivars Based on SSR
Markers Developed from the Whole Genome Sequence
ZHANG Dan1,SONG Chunyan1*,ZHANG Lujun1,WU Ping1,2,
BAO Dapeng1,SHANG Xiaodong1,TAN Qi 1
(1Institute of Edible Fungi,Shanghai Academy of Agricultural Sciences;Key Laboratory of Applied
Mycological Resources and Utilization,Ministry of Agriculture;National Research Center for Edible Fungi
Biotechnology and Engineering;Shanghai Key Laboratory of Agricultural Genetics and Breeding;Shanghai
201106,China;2 Colege of Life Sciences,Nanjing Agricultural University,Nanjing,Jiangsu 210095,China)
Abstract:Lentinula edodes is an important cultivated mushroom in China,and accurate and reliable
identification of individual cultivars is a prerequisite for successful cultivation and variety protection.In this
study,the whole genome sequence of L.edodes was used to generate 200simple sequence repeat(SSR)
markers for delineating 25commercial cultivars and for determining their genetic diversity.Our data revealed
a relatively high level of genetic similarity among the cultivars,with average,minimum and maximum genetic
similarity coefficient values of 0.776,0.567and 1.000,respectively.Seven SSR primer pairs delineated
eleven of the cultivars(Cr-02,Minfeng-1,Xianggu 241-4,Senyuan-1,Senyuan-8404,Xiang-9,Guangxiang-
51,Huaxiang-5,L952,L9319and L808)based on their unique multilocus SSR fingerprint profiles.
Key words: Lentinula edodes;simple sequence repeat; commercial cultivar; genetic diversity;
fingerprint profile
Lentinula edodes is an important edible
mushroom cultivated in China where,since the
1970’s,output has greatly increased due to the
expanded use of the sawdust substrate
cultivation system[1].According to statistics
from the China Edible Fungus Association,the
yield of L.edodes in 2012amounted to over
four milion tons(fresh weight),second only
to Pleurotus ostreatus,with more than 20
varieties currently under commercial-scale
cultivation.
Precise identification of commercial varieties
is of great importance for the Lentinulaindustry,
and both spawn producers and mushroom growers
have suffered huge economic losses due to the use
of deteriorated strains.Consequently,there is an
urgent need to develop methods for the rapid and
accurate identification of commercial L.edodes
cultivars.
In the past,registration and protection of
L.edodes strains relied on DUS(Distinctness,
Uniformity and Stability) testing, which
consists of expensive, space-and time-
consuming measurements of morphological
traits.In recent years,polymerase chain
reaction(PCR)-based molecular markers,such
as Random Amplified Polymorphic DNA
(RAPD)[2], Amplified Fragment Length
Polymorphism (AFLP)[3], Inter Simple
Sequence Repeats (ISSR)[4],and Sequence
Characterized Amplified Region (SCAR)[5-7],
have been used to distinguish commercial
ACTA EDULIS FUNGI Vol.21
strains.However,although these markers have
been highly valued during the past decade,
disadvantages in their practical application
have emerged in some cases.For example,
RAPD,AFLP and ISSR methodologies often
produce complex banding patterns, false
positives or negative results due to competitive
reactions and unstable annealing
temperatures[8].
With the development of DNA sequencing
technology,additional polymorphic molecular
makers such as SSR (Simple Sequence Repeat)
and SNP (Single Nucleotide Polymorphism)
have been used in strain identification.SSR
markers are co-dominant,highly polymorphic,
stable and exchangeable between laboratories,
and have proven valuable in identifying plant
varieties[9-12].Traditionaly,SSR primers were
developed using the Expressed Sequence Tags
(EST) database[13], the FIASCO (Fast
Isolation by AFLP of Sequences Containing
Repeats)enrichment procedure[14],or the
ISSR-suppression-PCR method[15]. However,
the number of available SSR markers developed
using the aforementioned methods has been
limited.Recently,folowing resolution of the
complete genome sequence of L.edodes,
numerous SSR loci have been identified.Using
this information, we have developed SSR
markers and constructed multilocus SSR
fingerprint profiles, which have important
application value for the rapid identification of
commercial strains and for revealing genetic
relationships between the main cultivated
varieties.
1 Materials and Methods
1.1Strains
Twenty-five L. edodes commercial
strains,cultivated throughout large areas of
China,were included in this study(see Table 1
in the Chinese version).
1.2DNA extraction
Flasks(250mL)containing 100mL potato
dextrose(PD)medium(potato 200g,dextrose
20g,tap water 1 L)were inoculated with
mycelium from a potato dextrose agar(PDA)
stock slant,and incubated at 25℃ with
shaking(140r/min)for seven days.Mycelium
was colected by filtration,and genomic DNA
was extracted using the cetyltrimethyl
ammonium bromide(CTAB)method[2,16].The
concentration and purity of DNA samples
were determined spectrophotometricaly
(NanoDrop-1000 type, Thermo Company,
USA),and only DNA samples with an OD260/
OD280value>2.0were retained.DNA samples
for each strain were diluted to 50g/μL with
ultrapure sterile water.
1.3Development of SSR primers
A total of 200candidate SSR primer pairs
were designed based on the whole genome
sequence of L.edodes using MISA
[17] and
Primer Premier 3.0 software[18],and were
synthesized by Sangon(Shanghai,China)Co.,
Ltd.
1.4SSR analysis
PCR reactions were carried out in a
Mycycler thermal cycler (Bio-Rad,USA).
Amplification was carried out in 20μL reaction
mixtures containing: 2μL 10× reaction
buffer,2 μL MgCl2 (25 mmol/L),0.4μL
dNTP (10 mmol/L),0.2μL Taq DNA
polymerase(5U/μL,Promega,USA),2μL
template DNA(50ng/μL),1.5μL+1.5μL
forward and reverse primers(10μmol/L)and
ddH2O to volume.
Amplification with SSR primers was
carried out using touchdown PCR
[19]as folows:
1cycle at 95℃for 5min;2cycles at 95℃for
30s,67℃for 50sand 72℃for 30s,then the
annealing temperature of the reaction was
decreased 2℃every second cycle from 67℃to
51℃,25cycles at 95 ℃for 30s,55 ℃for
50s,and 72 ℃for 30s,folowed by a final
extension at 72℃for 7min.
Electrophoresis and staining with silver nitrate
solution were as described in Reference[20].
01
No.2 ZHANG Dan,SONG Chunyan,ZHANG Lujun,et al
1.5Data analysis
Al the legible amplified DNA bands were
manualy scored either“1”when present or“0”
when absent.The Polymorphism Information
Content(PIC)of SSR markers was analyzed
by PowerMarker 3.0 software
[21],and the
genetic diversity analyses of commercial
cultivars were performed with NTsys 2.10
software[22].Simple Nei’s genetic distance
measurements were used to determine matching
coefficients (SM)between the L.edodes
cultivars.Cluster analyses were performed by
the Unweighted Pair Group Method with
Arithmetic Averages (UPGMA)using the
SAHN module of NTsys 2.10software.
SSR markers with the same annealing
temperature were selected to construct
fingerprint profiles.The size of each amplified
fragment was determined according to the
50bp DNA ladder marker (GeneRulerTM,
USA),and al the fragments of each SSR
marker were numbered consecutively from
high-to low-molecular weight.Cultivars were
differentiated by the combination of numbered
aleles.
2 Results and Analysis
2.1SSR marker polymorphism
Preliminary screening of the 200candidate
SSR primer pairs revealed that only 110of
these generated amplification products.
Polymorphism was observed in products
generated by 98primer pairs,accounting for
49%of the developed markers.A total of 545
distinct bands were detected by the 98
polymorphic SSR markers,and the number of
fragments amplified by each SSR primer ranged
from 2to 12.The average PIC value of
polymorphic SSR markers was 0.458 with a
maximum of 0.863and a minimum of 0.077.
2.2Genetic diversity among the commercial
cultivars
Twenty-five commercial L.edodes strains
were differentiated according to the
electrophoresis pattern of amplified fragments
of 98polymorphic SSR markers.The average
genetic similarity coefficient was 0.776,with a
maximum of 1and a minimum of 0.567.A
genetic similarity coefficient value of 0.73
separated al the cultivars into three groups
(see Fig.1in the Chinese version).Group I
included Shen-8,Shen-10,Shen-12,Xiangza-
26, Wuxiang-1, Cr04, Junxing-8, Cr62,
Ganxiang-1,Huaxiang-8,Minfeng-1,L9319,
Cr02,Senyuan-1,Huaxiang-5,L808and L952.
Group II included Qingyuan9015, Jingdi,
Xianggu241-4,Senyuan8404,L135,Senyuan-
10 and Guangxiang-51, while Group III
contained only strain Xiang-9.
Genetic diversity analysis revealed the
genetic background of the 25test strains to be
very similar.The average genetic similarity
coefficient of Shen-8, Shen-10, Shen-12,
Xiangza-26,Wuxiang-1,Cr04and Junxing-8
was 0.998.The corresponding value for 241-4
and Senyuan8404 was 0.991, while the
similarity coefficient for Cr62,Ganxiang-1and
Huaxiang-8, Qingyuan9015 and Jindi,and
L135and Senyuan-10was 1.0in al three cases.
2.3Multilocus molecular phenotypes of the
test strains
The 25cultivars were separated into 15
groups at a genetic similarity coefficient setting
of 0.99.Seven SSR markers were selected to
distinguish between these 15groups(see Table
2in the Chinese version).Fragments amplified
from each locus by each primer pair ranged
from 2to 5in number,and were number-coded
from high(930bp)to low (260bp)size(see
Table 2in the Chinese version).
Using the seven primer pairs,a total of 15
multilocus molecular phenotypes,characterized
by the electrophoresis patterns of the amplified
fragments,were delineated among the 25test
strains(see Table 3in the Chinese version).A
total of 20clear,stable and reproducible bands
were selected.
Based on the fragment patterns,eleven
11
ACTA EDULIS FUNGI Vol.21
cultivars(Cr-02,Minfeng-1,241-4,Senyuan-
1,Senyuan8404, Xiang-9, Guangxiang-51,
Huaxiang-5,L952,L9319 and L808)were
distinguished individualy,while the remaining
14strains were divided into four groups:Group
A comprised strains Shen-8,Shen-10,Shen-12,
Cr-04,Wuxiang-1,Xiangza-26and Junxin-8,
Group B strains Cr-62, Ganxiang-1 and
Huaxiang-8,Group C strains Qingyuan9015
and Jindi,and Group D strains L135 and
Senyuan-10.The multilocus SSR fingerprint
profiles of three individualy delineated L.
edodes cultivars are shown in Fig.2(see the
Chinese version).
3 Discussion
SSR markers are codominant and
polymorphic,and are widely used in various
research fields such as genetic linkage
mapping, molecular ecology and genetic
diversity[23-26]. With the development of
genome sequencing technology,an increasing
number of SSR markers have been developed.
A total of 277062SSRs,representing 8%of the
assembled genomic sequence, have been
detected in Laccaria bicolor[17,27].Seventeen
polymorphic SSR markers were cloned by the
FIASCO enrichment procedure and used to
differentiate Auricularia auricula-judae
cultivars[14],and SSRs have also been identified
in the genome of Ganoderma lucidum[28].A
combination of only three selected SSR markers
was sufficient to discriminate unambiguously 27
of 28 Agaricus bisporus genotypes[29].
In this study,2 0 0 SSR markers were
developed from the genomic sequence of L.
edodes.Based on genotypic data,seven SSR
markers delineated 2 5 Chinese commercial
L.edodes cultivars,1 1as individual strains
and the remaining 1 4into four groups.It is
noteworthy that the annealing temperature
was the same for al seven SSR primer pairs
used to amplify the markers, thereby
alowing the adoption of a constant PCR
program when preparing multilocus SSR
fingerprint profiles.
Currently, relatively few commercial
mushroom cultivars are used in China.
However, continuing development of the
mushroom industry wil necessitate accurate
methods of strain identification and
certification.With the development of genome
sequencing technology,SSR makers developed
from the whole genome sequence,appear to
have major potential application value in
constructing fingerprint profiles of mushroom
strains.
References
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early cultivation of Lentinus in China [J].
Mushroom J Trop,1987,7:31-37.
[2] ZHANG Y, MOLINA FI.Strain typing of
Lentinula edodes by random amplified polymorphic
DNA assay[J].FEMS Microbiol Lett,1995,131
(1):17-20.
[3]LO TC,KANG MW,WANG BC,et al.Glycosyl
linkage characteristics and classifications of exo-
polysaccharides of some regionaly different strains
of Lentinula edodes by amplified fragment length
polymorphism assay and cluster analysis[J].Anal
Chim Acta,2007,592(2):146-153.
[4]ZHANG RY,HUANG CY,ZHENG SY,et al.
Strain-typing of Lentinula edodes in China with
inter simple sequence repeat markers[J].Appl
Microbiol Biotechnol,2007,74(1):140-145.
[5]WU XQ,LI HB,ZHAO WW,et al.SCAR makers
and multiplex PCR-based rapid molecular typing of
Lentinula edodes strains[J].Curr Microbiol,2010,
61(5):381-389.
[6]LI HB,WU XQ,PENG HZ,et al.New available
SCAR markers:potentialy useful in distinguishing a
commercial strain of the superior type from other
strains of Lentinula edodes in China[J].Appl
Microbiol Biotechnol,2008,81(2):303-309.
[7]QIN LH,TAN Q,CHEN MJ,et al.Use of
intersimple sequence repeats markers to develop
strain-specific SCAR markers for Lentinula edodes
[J].FEMS Microbiol Lett,2006,257(1):112-116.
[8]LIU JY,YING ZH,LIU F,et al.Evaluation of
the use of SCAR markers for screening genetic
21
No.2 ZHANG Dan,SONG Chunyan,ZHANG Lujun,et al
diversity of Lentinula edodes strains[J].Curr
Microbiol,2012,64(4):317-325.
[9]DELGADO-MARTINEZ FJ, AMAYA I,
SANCHEZ-SEVILLA JF,et al. Microsatelite
marker-based identification and genetic relationships
of olive cultivars from the Extremadura region of
Spain[J].Genet Mol Res,2012,11(2):918-932.
[10]ERCISLI S,IPEK A,BARUT E.SSR marker-
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