Genetic Diversity and Taxonomic Implication of

Genetic Diversity and Taxonomic Implication of
Genetic Diversity and Taxonomic Implication of

Biochemical Genetics,Vol.37,Nos.5/6,1999

Genetic Diversity and Taxonomic Implication of Cordyceps sinensis as Revealed by RAPD Markers Yongjiu Chen,1Ya-Ping Zhang,1,3Yuexiong Yang,2and Darong Yang2 Received1Dec.1998DFinal2Apr.1999

Random ampli?ed polymorphic DNA(RAPD)markers are used to investigate genetic variation and evolutionary relationships of29samples of Cordyceps sinensis from different geographical populations on the Qinghai±Tibet plateau. Out of137RAPD bands scored,100are polymorphic.A correlation is revealed between geographical distance and genetic distance.The molecular phylogenetic tree suggests that the29samples are divided into three notable clusters, corresponding to the geographical populations,i.e.,the north population(NP), middle population(MP),and south population(SP).The NP consists of7 northern samples from Menyuan,Maqu,and Luqu,the MP consists of8samples from Yushu and Chengduo,and the SP consists of14samples from Byma Snow Mountain,Renzhi Snow Moutain,Chongcaoxiwa,and Dacaodi.It is demon-strated that extensive genetic diversity is found among different geographical populations of C.sinensis.The genetic diversity pattern of C.sinensis may be caused by the founder effects.The taxonomic status of NP,MP,and SP popula-tions should be that they are different subspecies rather than different species. KEY WORDS:Cordyceps sinensis;RAPD;genetic diversity;taxonomy.

INTRODUCTION

Cordyceps sinensis is one of the most valuable medicinal fungi native to China.It parasitizes a caterpillar(including several species of the genus Hepialus)that 1Laboratory of Cellular and Molecular Evolution,Kunming Institute of Zoology,Chinese Academy of Sciences,Kunming,Yunnan650223,China.

2Laboratory of Entomology,Kunming Institute of Zoology,Chinese Academy of Sciences,Kunming, Yunnan650223,China.

3To whom correspondence should be addressed.e-mail:zhangyp@https://www.360docs.net/doc/c015872483.html,.

201

0006-2928/99/0600-0201$16.00/0r1999Plenum Publishing Corporation

202Chen,Zhang,Yang,and Yang burrows underground and sprouts as a protruding fungus in summer(Jin and Lu, 1986).The life cycle of this fungus includes sexual and asexual generations.The sexual generation lives only in forests and is usually called``the Chinese herb’’or ``winter worm,summer grass’’(Chu,1965;Jin and Lu,1986).

C.sinensis is distributed only in western China,mainly in northern Yunnan, northeastern Qinghai,northwestern Sichuan,and eastern Tibet,where the terrain slopes down from northwest to southeast,and precisely in the eastern extension area of the Qinghai±Tibet plateau(Jin and Lu,1986;Wang,1997).C.sinensis has been used extensively as a medicinal organism.Its medicinal functions,such as improvement of immunity and prevention and treatment of acute renal failure (ARF),leukocythem ia,and hepatocirrhosis,have been reported in many studies (Chou and Lin,1994;Zheng et al.,1994;Xu and Chen,1995;Wang et al.,1996; Jia and Lau,1997).However,the classi?cation and evolution of the species are still open questions.

Random ampli?ed polymorphic DNA(RAPD),a simple polymerase chain reaction(PCR)ampli?cation of genomic DNA by a single synthetic oligonucleo-tide primer,can generate a complex pattern(Williams et al.,1990;Welsh et al., 1991).Because the RAPD technique usually reveals considerable polymorphism in genomic DNA,it has been extensively used as a genetic marker for estimating genetic,taxonomic,and phylogenetic relationships of plants and animals(Wil-liams et al.,1990;Welsh et al.,1991;Wachira et al.,1995;Chen et al.,1998).

Most previous studies of C.sinensis have focused on morphology,ecology, and cultivation of the asexual stage(Li and Sun,1988;Liu et al.,1989;Yin and Shen,1990;Zang et al.,1990;Liang,1991).Despite its medicinal uses,no studies have been reported evaluating the potential value of genetic markers in aiding breeding and conservation.Genetic studies may shed light on the evolution of C. sinensis.This paper employs RAPD markers to investigate the genetic diversity and evolutionary relationships of C.sinensis.

MATERIALS AND METHODS

Materials

Twenty-nine samples of C.sinensis and three samples of https://www.360docs.net/doc/c015872483.html,itaris were collected at the sites shown in Fig.1.

Genomic DNA Extraction

High molecular weight genomic DNA was extracted by the following procedures.

A eld-collected fungus sample(about500mg)was scraped and placed into700 l preheated extraction buffer(2%CTAB,1.4M,NaCl,0.2%2-mercaptoethanol, 20m M EDTA,100m M Tris±HCl,pH8.0).The sample was incubated at60êC in

a water bath for 1±2hr with optional occasional gentle swirling,then extracted with an equal volume of phenol and chloroform ±isoamyl alcohol (24:1)by mixing gently but thoroughly (Jeffrey,1991).The aqueous phase was transferred to a fresh Eppendorf tube.The DNA was precipitated at room temperature for 10min by adding 1vol of isopropanol containing 0.2M NaCl.After centrifugation at 3000rpm for 6min,the genomic DNA was air-dried and then dissolved in an appropriate volume of TE buffer (10m M Tris±HCl,1m M EDTA,pH 8.0).It was stored at 4êC until used.

PCR Program and RAPD Products

An American Stratagene Robocycler Gradient 40PCR ampli?er was used to amplify DNA.Primers in the PCR consisted of 10bp 60%G C (products of Operon Technologies Company).Forty primers were arbitrary used and tested in a few samples to determine which can generate clear bands.We selected 18of the primers to investigate genetic variation of C.sinensis.A 10-l RAPD reaction

Fig.1.1±10stand for areas of Menyuan,Luqu,Maqu,Yushu,Chengduo,Byma Snow Mountain,Renzhi Snow Mountain,Chongcaoxiwa,Dacaodi,and Kunming,respectively.Cor 01±03are clones of https://www.360docs.net/doc/c015872483.html,itaris from 2000-to 2200-m elevations at Kunming;Cor 04±07,Cor 08±10,Cor 11±14,Cor 15±17,Cor 18±19,Cor 20±21,Cor 22±24,Cor 25±27,and Cor 28±32are 29clones of C.sinensis from 3800to 4600-m elevations at Byma Snow Mountain,Renzhi Snow Mountain,Chong-caoxiwa,Dacaodi,Maqu,Luqu,Menyuan,Yushu,and Chengduo,respectively.

Genetic Diversity of C.sinensis 203

204Chen,Zhang,Yang,and Yang contained10m M Tris±HCl,pH9.0,50m M KCl,2.5m M MgCl2,0.001%gelatin, a0.1mM concentration each of dATP,dCTP,dGTP,and dTTP,a0.1m M concentration of each primer,25ng of genomic DNA,and1.0U of Taq DNA polymerase(products of Sino±American Biotechnology Company),and the mixture was covered with20l oil.

The PCR program included40cycles,each cycle with denaturing for60sec at94êC,annealing for60sec at36êC,extension for120sec at72êC,predena-turing for200sec at95êC before the rst cycle,and extension for300sec at 72êC after the last cycle.A blank control was run in each of the PCRs.The ampli?ed products were separated by electrophoresis in 1.5%agarose gels (containing0.05g/ml ethidium bromide)and observed and photographed under ultraviolet light(Williams et al.,1990;Welsh et al.,1991;Wachira et al.,1995; Chen et al.,1998).

Data Analysis

Although visualization of different-sized DNA fragments on agarose gels did not exclude the possibility that some may contain homologous DNA sequences,for the purposes of data analysis,each sample of primer-speci?c ampli?cation product was considered to represent the dominant allele at a unique RAPD band. ``0’’and``1’’stand for fragment absent and fragment present,respectively (Wachira et al.,1995;Chen et al.,1998).

The genetic distance(D)between two samples was calculated using D

1F,where F is an estimation of the similarity,which was based on the fraction of shared RAPD bands.It could be calculated by the formula F2N xy/(N x N y), where N xy is the number of ampli?ed DNA fragments with the same molecular weight found in both samples,N x is the total number of fragments found in one sample(No.x),and N y is the total number of fragments found in the other sample (No.y)(Nei and Li,1979).

The phylogenetic tree was based on genetic distances and prepared by the unweighted pair group method with arithmetic(UPGMA)in PHYLIP version3.5 (Sneath and Sokal,1973).

The degree of polymorphism was estimated by Shannon’s index of pheno-typic diversity.H o i ln i,H pop1/n(H o),H sp ln,where i and are frequencies of phenotypes;H o can be calculated and compared for differ-ent populations;H pop is the average diversity over the n different populations,and H sp is the diversity calculated from the phenotypic frequencies,,in all the populations considered together.The proportion of diversity H pop/H sp(H sp H pop)/ H sp was compared within populations and between populations(Wachira et al., 1995).

Genetic Diversity of C.sinensis205

RESULTS

RAPD Analysis

Of29samples of C.sinensis,all18arbitrary primers used for estimating genetic relationships generate polymorphic patterns.Of137bands scored,100are polymorphic.Distributions of polymorphism based on RAPD electrophoreses are given in Table I.Figure2shows electrophoresis results of PCR products by primer OPH03.

Genetic Distance and Phylogenetic Tree

Genetic distances(D)and a phylogenetic tree are shown in Table II and Fig.3, respectively.The topology of the UPGMA tree suggests that29samples of C. sinensis(Cor04±32)can be divided into three notable clusters corresponding to their geographical populations,i.e.,the north population(NP),middle population (MP),and south population(SP),when three samples of https://www.360docs.net/doc/c015872483.html,itaris(Cor01±03) are used for rooting the tree.The NP consists of7samples from Menyuan,Luqu, and Maqu in northern areas of the Qinghai±Tibet plateau,the MP consists of8 samples from Yushu and Chengduo in the middle areas of the plateau,and the SP consists of14samples from Byma Snow Mountain,Renzhi Snow Mountain, Chongcaoxiwa,and Dacaodi in southern areas of the plateau.

Genetic Diversity

Considering the molecular phylogenetic tree,we divided the samples into the three populations(NP,MP,and SP)for estimating the genetic diversity of C. sinensis.The average partitioning of genetic diversity over the three populations (H pop)is0.7397,and that in all the populations(H sp)is1.4547;the average proportions of diversity within populations(H pop/H sp)and among populations (H sp H pop)/H sp are0.5085and0.4915,respectively.Table III displays the18 primers used in RAPD markers and Shannon’s index.

DISCUSSION

It has been demonstrated that RAPD markers are useful for studying the genetic diversity and evolution of C.sinensis.Of the18arbitrary primers used,none generates a monomorphic pattern,and none of the29samples of C.sinensis displays identical RAPD patterns.The size of the ampli?ed fragments scored ranges from0.36to2.3kb,which is in agreement with previous studies(Williams et al.,1990;Welsh et al.,1991;Wachira et al.,1995;Chen et al.,1998).

The topology of the phylogenetic tree of C.sinensis corresponds to their

T a b l e I .D i s t r i b u t i o n s o f R A P D B a n d P o l y m o r p h i s m s i n 18A r b i t r a r y P r i m e r s o f 3C l o n e s o f C .m i l i t a r i s a n d 29C l o n e s o f C .s i n e n s i s :C o r 01±32C o r r e s p o n d t o C o r 01±32i n F i g .

1

206

Chen,Zhang,Yang,and Yang

F i g .2.R A P D r e s u l t s f o r 29c l o n e s o f C .s i n e n s i s a m p l i e d b y O P H 03.M i s D N A (d i g e s t e d b y H i n d I I I /E c o R I );01±29c o r r e s p o n d t o C .s i n e n s i s C o r 04±32i n F i g .1,r e s p e c t i v e l y .

Genetic Diversity of C.sinensis

207

geographical distributions.The three isolated geographical populations which are distributed in the northern,middle,and southern regions of the Qinghai±Tibet plateau are three clusters,respectively,i.e.,the NP,MP,and SP.Meanwhile,samples of C.sinensis which are distributed in the same geographical area are usually grouped together except for one individual at Yushu according to our molecular phylogenetic tree.

Partitioning of the genetic variation in C.sinensis indicates that,on average,51%is distributed within populations and 49%between populations.Because no other periphthecial Ascomycetes or other members of the Ascomycetes are available,we used the outbreeding woody plants for comparison.The outbreeding woody plants retained considerable variability and most variation is exhibited within populations (Hamrick,1990).Seventy percent of the genetic variation is within,and 30%between,tea populations (Wachira et al.,1995).However,the genetic variation between populations of C.sinensis is relatively high.It has been demonstrated that extensive genetic diversity is found among different popula-tions of C.sinensis.

Table II.Genetic Distance (D )Based on the Fraction of Shared RAPD Bands:Cor 01±32

Correspond to Cor 01±32in Fig.

1

208Chen,Zhang,Yang,and Yang

The Qinghai±Tibet plateau is the ridge of the world,and its average altitude is 4000m above sea https://www.360docs.net/doc/c015872483.html,ually,the altitudes of the tops of mountains on the plateau are above 5000m,whereas the bases are below 3000m (Yang,1997).C.sinensis is distributed only at 3500-to 5000-m altitude,so unusually it is found at the bases of the mountains (Jin and Lu,1986).The spread of C.sinensis,depending on the shooting of their ascospores,is limited to certain areas in a mountain and is unlikely through discontinuous mountains.So gene ˉow between different populations on discontinuous mountains is generally lower.However,the mountains in Yushu and Chengduo are ˉatter,and the bases are not as low as in other areas.Some C.sinensis samples may live at the bases of the mountains where the altitude is greater than 3500m.Thus,C.sinensis can spread more easily among those discontinuous mountains,and gene ˉow probably occurred between populations.Therefore,the genetic diversity pattern of C.sinensis observed in this study may be caused by founder effects.

The shapes of ascus and ascospore among different populations of C.sinensis vary considerably.Zang et al.(1990)described a new species of Cordyceps crassispora at Byma Snow Mountain having a much shorter ascus

Table II.

(continued)

Genetic Diversity of C.sinensis 209

Fig.3.Molecular phylogenetic tree of 29clones of C.sinensis,and 3clones of https://www.360docs.net/doc/c015872483.html,itaris by the unweighted pair group method with arithmetic (UPGMA)method.Cor 01±32are the same as Cor 01±32in Fig.1.

210Chen,Zhang,Yang,and Yang

Genetic Diversity of C.sinensis211 Table III.Partitioning of Genetic Diversity Into,Within,and Between Populations for18Primers

a NP stands for Maqu,Luqu,and Menyuan in the north of the Qinghai±Xizang plateau;MP,for Yushu and Chengduo in the middle of the plateau;and SP,for Byma Snow Mountain,Renzhi Snow Moun-tain,Chongcaoxiwa,and Dacaodi in the south of the plateau.

(170±2207.5±10.4m)and a wider and shorter segment of the ascospore (one-celled segment, 6.5±9.8 5.2±6.5m),but the ascus of C.sinensis is always longer(220±28013m),and the ascospore is liform,not clavate,and breaks into a one-celled,slightly narrower partDa spore(9±154±5m). However,while studying the type specimen of C.sinensis kept in the Herbarium of the Royal Botanic Garden,Zang and Kinjo(1996)found that the ascus is 160±240 5.2±6.5(12)m,although it may not be fully mature,and the ascospore is120±1900.6±1.3m.So this standard for classi?cation of C. sinensis may be controversial because not only is there some overlap in ascus size, but also there is a morphological variation gradient of acsus and ascospore among these two supposedly different species.Of the ascus and ascospore of the29 samples in our study,the SP from Byma Snow Mountain,Renzhi Snow Mountain, Chongcaoxiwa,and Dacaodi is more similar to C.crassispora,the NP from Maqu,Luqu,and Menyuan is more similar to the type specimens of C.sinensis, and the MP from Yushu and Chengduo is intermediate between the two.There seems to be also a general geographical separation among these phenotypes.This implies that the taxonomic status of the NP,MP,and SP populations should be as different subspecies,rather than as different species.

212Chen,Zhang,Yang,and Yang In addition,the resource of C.sinensis is rapidly being exhausted due to overexploration and serious destruction of the living environments(Wang,1997). So it is urgently necessary to devise a sound plan for conserving this precious medicinal resource.On the other hand,no sexual sample of C.sinensis from arti?cial cultivation has been developed yet.Our genetic studies will be useful for conservation of the resource and cultivation of sexual samples of C.sinensis.

ACKNOWLEDGMENTS

This study was supported by the National Science Foundation of China and the Natural Science Foundation of Yunnan Province.We thank Drs.Xianwei Shi and Yongfu Huang,Misses Chunling Zhu and Jing Qi,and Messrs.Shikang Gou and Farong Shen for their help.

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驱动电路设计

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MOS管及MOS管的驱动电路设计

MOS管及MOS管的驱动电路设计 MOS管及MOS管的驱动电路设计 摘要:本文将对MOSFET的种类,结构,特性及应用电路作一简单介绍,并控讨了一下MOSFET驱动电路设计问题在使用MOS管设计开关电源或者马达驱动电路的时候,大部分人都会考虑MOS的导通电阻,最大电压等,最大电流等,也有很多人仅仅考虑这些因素。这样的电路也许是可以工作的,但并不是优秀的,作为正式的产品设计也是不允许的。 1、MOS管种类和结构 MOSFET管是FET的一种(另一种是JFET),可以被制造成增强型或耗尽型,P沟道或N沟道共4种类型,但实际应用的只有增强型的N沟道MOS管和增强型的P沟道MOS管,所以通常提到NMOS,或者PMOS指的就是这两种。右图是这两种MOS管的符号。 至于为什么不使用耗尽型的MOS管,不建议刨根问底。 对于这两种增强型MOS管,比较常用的是NMOS。原因是导通电阻小且容易制造。所以开关电源和马达驱动的应用中,一般都用NMOS。下面的介绍中,也多以NMOS为主。 在MOS管原理图上可以看到,漏极和源极之间有一个寄生二极管。这个叫体二极管,在驱动感性负载(如马达),这个二极管很重要。顺便说一句,体二极管只在单个的MOS管中存在,在集成电路芯片内部通常是没有的。下图是MOS管的构造图,通常的原理图中都画成右图所示的样子。(栅极保护用二极管有时不画) MOS管的三个管脚之间有寄生电容存在,如右图所示。这不是我们需要的,而是由于制造工艺限制产生的。寄生电容的存在使得在设计或选择驱动电路的时候要麻烦一些,但没有办法避免,在MOS管的驱动电路设计时再详细介绍。

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