陆地棉EST长度多态性与其SSR分布特征相关性分析

目的:分析陆地棉EST长度多态性与其SSR分布特征的相关性。方法:从NCBI公共数据库下载陆地棉EST序列,应用SSRIT搜索SSR,分析20 000条无冗余的EST序列。结果:在剔除低质量和冗余的序列后,得到全长为7 363.878kb的无冗余EST序列7 322条,其中含有SSR位点的EST序列数520条,占被分析EST比例的2.60%。长度在400bp以下的EST序列含SSR的比例为1.46%;长度在400bp以上的EST序列含SSR的比例为8.94%。在1～6bp的重复基元中,二核苷酸重复基元的SSR重复频率最高,占总数的63.46%,其次是三核苷酸,占总数的34.04%。二核苷酸类型(AG)n、(AT)n和三核苷酸类型(AAG)n、(ACC)n、(ACT)n、(AAT)n是SSR的主要重复基元。结论:棉花EST-SSR可用于棉花分子标记,为有针对性设计陆地棉EST-SSR引物奠定基础。     

鲫鱼(Carassius auratus)表达序列标签资源的SSR构成与分布分析

分析鲫鱼EST资源的SSR信息,为开发EST-SSR标记奠定基础.从GenBank中获得鲫鱼EST序列,然后用Sequencher 4.8软件进行序列拼接得到Uni-EST序列,再通过SciRoKo 3.4软件扫描Uni-EST序列中的SSR,最后得出EST-SSR的分布特征、频率和重复基元类型等特征.通过搜索共获得9 230条鲫鱼EST原始序列,通过使用计算机软件进行预处理共得到全长为3.81×106 bp的无冗余Uni-EST 7 092条.在这些序列中共搜索出597个SSR位点,分布在545条Uni-EST序列中,发生频率为8.13％,EST-SSR的平均长度为(19.34±6.23) bp,平均每Mb含156.55个SSR位点.单核苷酸重复在鲫鱼EST-SSR中占主导地位,发生频率为39.53％,其次为二核苷酸重复,发生频率为36.68％以及三核苷酸重复的15.41％.在所有非单核苷酸重复基元中,AC基元出现频率最高,其次为AG.设计出引物404对.最后得出结论鲫鱼EST中SSR出现的频率较高,并且类型较为丰富,为进行遗传多样性分析和重要经济性状筛选等方面的研究提供了基础和指导.     

漆树EST-SSR引物开发

利用NCBI数据库进行漆树EST-SSR引物开发,从NCBI数据库中共下载漆树EST序列87 856条。利用MISA软件进行序列处理、拼接及聚类后,从87 856条漆树EST序列中拼接组装成3 979条非冗余序列,含SSR位点的EST序列出现频率占EST序列总数的4.5%,从3 979条非冗余序列中检测到487个SSRs微卫星位点,出现频率为12.2%。这些SSR位点中,三核苷酸和二核苷酸重复基元所占比例较高。采用Primer5.0软件,共成功设计50对EST-SSR引物,50对EST-SSR引物在25个漆树个体上均能扩增出清晰的电泳条带,其中18对引物检测出了多态性条带,扩增率达36%。     

甜瓜EST序列中微卫星的分布特征

GenBank中35547条甜瓜EST经去冗余处理后,得到总长度为250.3Mb的无冗余EST34438条。这些序列中有2813个微卫星简单重复序列（Simple sequence repeat,SSR）,分布于2107条EST中,出现频率为8.16%,平均分布距离为8.90kb。三核苷酸重复是主导重复类型,占SSR总数的47.14%;其次是二核苷酸和单核苷酸重复,分别占SSR总数的20.72%和16.99%。AAG/TTC是优势重复基元,占微卫星总数的29.26%,AG/CT和A/T分别占14.61%和16.25%。在所有的SSR中,重复次数为4～10次的占70.32%,长度为12～20bp的占51.12%。并对这些SSR的多态性潜能进行了评价。     

家蚕第12连锁群EST-SSR标记的筛选和分析

为了探究家蚕Bombyx mori EST-SSR标记的多态性, 对检索获得的家蚕第12连锁群的4 465条EST序列进行了分析, 整理和拼接后得到581条非冗余EST序列, 总长度约为480 kb。其中, 有122条序列中共检测到154个EST-SSR, 占所研究的EST序列的2.73%, 平均每3.12 kb 含有一个EST-SSR。在所检测的EST-SSR中, 三核苷酸和四核苷酸重复是主导类型, 分别占总数的36.36%和28.57%,大部分表现为Perfect形式; 核苷酸重复平均长度约为16.2 bp, 最长为30 bp。进一步进行同源性分析, 发现有26条序列可以在NCBI中检索到同源序列, 在这些序列中一共含有40个SSR, 其中14个(35.0%)位于5′-UTR, 11个(27.5%)位于3′-UTR, 15个(37.5%)位于CDS区。根据筛选到的微卫星序列设计11对引物, 其中8对引物有扩增产物, 且条带清晰; 应用引物ES1204对8个家蚕品种进行PCR扩增都呈现多态性。结果说明通过家蚕EST数据库发掘SSR标记是一条可行的途径。     

番红花EST资源的SSR信息分析

从NCBI公共数据库下载得到6745条番红花EST,通过前处理得到全长为612.01 kb的无冗余EST 1431条.在这些序列中搜索出108个SSR,分布于103条EST中,出现频率为7.55%.这些EST-SSR的平均分布距离是5.67 kb.二核苷酸重复和三核苷酸重复是番红花主要的重复类型,分别占总EST-SSR...     

烟草ESTs资源的SSR信息分析

烟草ESTs数量迅速增加为开发新的SSR标记提供了宝贵的资源.经过软件分析,对242 683条烟草ESTs序列剔除冗余序列,在211 728条非冗余烟草ESTs序列中,共检索出9 339个SSR,SSR之间的距离约为14.21 kb,检出率为4.41%,包括216种重复基元.其中三核苷酸重复类型的SSR占主导地位,占总SSR的50.34%,其次为二核苷酸和单核苷酸,分别为23.00%,16.48%,其余重复类型所占比例均不足5%.在所有重复基元中,A/T重复为主要类型,占所有重复14.68%,其次为AT/TA、AG/TC、AAG/TTC,分别为10.49%、9.48%、6.85%.随机设计10对EST-SSR引物,对6个品种烟草进行扩增,10对EST-SSR引物均能扩增出产物,其中1对引物在6个品种有多态性.本研究为烟草EST-SSR标记的建立和进一步应用奠定了基础.     

三种人参属植物的EST-SSR信息分析及其在三七中的应用

为了解人参属植物EST中SSR分布特点及其在三七SSR标记中的应用,利用生物信息学方法,用primer 3软件对dbEST数据库中人参属植物人参、西洋参和三七的EST序列进行搜索,发现人参属植物EST-SSR出现频率为11.54%,平均每4.39 kb出现1个SSR.人参属植物单核苷酸重复基元占主导地位,其次为三核苷酸重复基元和二核苷酸重复基元,分别占总SSR的54.48%、17.31%和16.36%.人参属EST-SSR的优势类型为A/T和AT/TA,分别占54.73%和8.21%.根据人参属植物EST中的SSR设计48对引物,在合适的PCR扩增体系下,用5个三七样品的DNA为模板进行PCR扩增,引物有效扩增率85.42%,其中多态性引物占可扩增引物的70.73%.结果表明,利用人参属EST序列开发三七EST-SSR标记是可行的.     

甘薯与牵牛EST资源的SSR信息分析

为挖掘番薯（Ipomoea）属EST-SSR资源,从NCBI数据库下载23406条甘薯（Ipomoea batatas (L.) Lam.）EST和62282条牵牛（Ipomoea nil (L.) Roth）EST,利用生物信息学软件预处理、去冗余、拼接处理后得到12812条无冗余的甘薯EST（6.70 Mb）和28422条牵牛唯一序列（17.19 Mb）。对这些序列进行SSR搜索,在甘薯上获得328个SSR位点,发生频率为2.56%;牵牛上筛选到962个SSR位点,出现频率为3.38%。甘薯和牵牛EST-SSR具有多个共同特征：在SSR位点中,主要是二核苷酸重复类型,其次是三核苷酸重复;在二核苷酸重复中,出现最多的重复基序为AG/CT,其次是AT/AT;在三核苷酸重复中,主要基序是AAG/CCT;SSR位点的长度主要集中在20~22 bp。结果表明,这些搜索出的EST-SSR重复基序类型丰富、多态性潜能高,具有较高的开发和利用价值。     

黄瓜基因组EST-SSRs的分布规律及EST-SSR标记开发

从NCBI网站下载黄瓜EST序列6 344条及本课题组对黄瓜叶片cDNA文库测序研究所得的EST 163条,在除去载体、polyA/T等序列后得到6 129条无冗余EST序列,全长为2.98×106bp.采用网络软件SSRIT从这些序列中搜索到784个SSR,分布于673条EST中,出现频率为12.79%,平均分布距离为3.80 kb;单、二和三核苷酸重复是主导类型,分别占EST-SSRs总数的32.91%、28.19%和29.34%;A/T、AG/CT和AAG/CTT分别是单、二和三核苷酸的优势重复基元,分别占EST-SSRs总数的32.40%、20.66%和14.41%.经现已报道的评价方法分析表明,这些EST-SSRs具有较好的多态性和可用性.设计了30对EST-SSR引物对22份黄瓜材料进行PCR检测,18对引物检测到多态性.根据PCR结果,这些材料被聚为三类,聚类结果与材料本身特性一致.结果说明通过黄瓜EST数据库发掘SSR标记是一条可行的途径.     

Identification and characterization of SSRs from soybean (Glycine max) ESTs

Microsatellites, or simple sequence repeats (SSRs), are very useful molecular markers for a number of plant species. We used a new publicly available module (TROLL) to extract microsatellites from the public database of soybean expressed sequence tag (EST) sequences. A total of 12,833 sequences containing di- to penta-type SSRs were identified from 200,516 non-redundant soybean ESTs. On average, one SSR was found per 7.25?kb of EST sequences, with the tri-nucleotide motifs being the most abundant. Primer sequences flanking the SSR motifs were successfully designed for 9,638 soybean ESTs using the software primer3.0 and only 59 pairs of them were found in earlier studies. We synthesized 124 pairs of the primers to determine the polymorphism and heterozygosity among eight genotypes of soybean cultivars, which represented a wide range of the cultivated soybean cultivars. PCR amplification products with anticipated SSRs were obtained with 81 pairs of primers; 36 PCR products appeared to be homozygous and the remaining 45 PCR products appeared to be heterozygous and displayed polymorphism among the eight cultivars. We further analysed the EST sequences containing 45 polymorphic EST-SSR markers using the programs BLASTN and BLASTX. Sequence alignment showed that 29 ESTs have homologous sequences and 15 ESTs could be classified into a Uni-gene cluster with comparatively convincing protein products. Among these 15 ESTs belonging to a Uni-gene cluster, 9 SSRs were located in 3'-UTR, 4 SSRs were located in the intron region and 2 SSRs were located in the CDS region. None of these SSRs was located in the 5'-UTR. These novel SSRs identified in the ESTs of soybean provide useful information for gene mapping and cloning in future studies.     

茶树EST-SSRs分布特征及引物开发

为了在茶树中开发EST-SSRs功能性标记,利用生物信息学方法对NCBI网上公开的3288奈茶树（Camellia subebsus）ESTs序列进行EST-SSRs特征分析。剔除冗余序列,得到非冗余序列2083条。在非冗余序列中发现含不同重复基元SSRs的EST序列有385条,共486个EST-SSRs,平均相隔2．10kb出现1个SSR。在2～6bp的重复基元中,二核苷酸重复基元的SSRs出现频率最高（51．97％）,其次是三核苷酸（19．55％）。对所有的重复基元类型进行统计分析发现,所占比例最高的是AG／CT（47．74％）,其次分别是AT／TA（4．73％）和AAG／CTT（4．73％）。利用Prime5软件,设计了206对EST-SSRs引物,随机选用72对引物进行SSR扩增,发现31对引物可以扩增出条带,其中29对引物具有多态性,多态性比率为93．5％。这些EST-SSRs将有助于茶树基因组学方面的研究。     

蝴蝶兰EST-SSRs分析

对蝴蝶兰属EST序列进行了SSR分析。蝴蝶兰属EST总长为4.5Mb,含有609个SSR。SSR出现频率7.65%,平均距离7.39kb,平均长度为22.17bp。单碱基、二碱基和三碱基重复是主要重复类型,分别占EST-SSR总数的21.67%、40.39%和33.50%。A、AG和CCG分别是单碱基、二碱基和三碱基重复中主导重复基元,分别占96.21%、58.54%和32.25%。设计引物及检测的结果表明,蝴蝶兰EST-SSR标记对兰科其他属植物具有一定的通用性。     

烟草EST-SSR位点分析

利用MISA软件对烟草EST公共数据库中的简单重复序列(SSRs)进行了分析。结果表明,在133523条EST序列中,共获得81757条SSR序列,SSRs之间的距离约为0.92 kb。其中,六碱基重复丰度最大,占60.3%,而单碱基、三碱基、四碱基、二碱基和五碱基重复丰度分别为20.0%、11.0%、4.2%、2.8%和1.7%。在单碱基、二碱基、三碱基和四碱基重复模体中,丰度最大的分别是A/T、AG、AAG和AAAT,而CG在编码区内丰度很低。用CAP3软件进行冗余分析表明,在这6种类型的重复模体中,冗余与非冗余的烟草EST之间没有显著差异。在得到的SSR序列中随机选择10个序列设计引物,在7个烟草品种中进行PCR扩增。结果表明,10对引物全部扩增出PCR产物,其中8对引物扩增出预期片段。用这8组扩增出预期片段的PCR产物进行变性PAGE凝胶电泳检测,结果表明,其中有4对引物(EB4、EB5、EB6和EB8)扩增出多态性条带。     

SSR mining in coffee tree EST databases: potential use of EST-SSRs as markers for the Coffea genus

Expressed sequence tags (ESTs) from Coffea canephora leaves and fruits were used to search for types and frequencies of simple sequence repeats (EST–SSRs) with a motif length of 1–6 bp. From a non-redundant (NR) EST set of 5,534 potential unigenes, 6.8% SSR-containing sequences were identified, with an average density of one SSR every 7.73 kb of EST sequences. Trinucleotide repeats were found to be the most abundant (34.34%), followed by di- (25.75%) and hexa-nucleotide (22.04%) motifs. The development of unique genic SSR markers was optimized by a computational approach which allowed us to eliminate redundancy in the original EST set and also to test the specificity of each pair of designed primers. Twenty-five EST–SSRs were developed and used to evaluate cross-species transferability in the Coffea genus. The orthology was supported by the amplicon sequence similarity and the amplification patterns. The >94% identity of flanking sequences revealed high sequence conservation across the Coffea genus. A high level of polymorphic loci was obtained regardless of the species considered (from 75% for C. liberica to 86% for C. canephora). Moreover, the polymorphism revealed by EST–SSR was similar to that exposed by genomic SSR. It is concluded that Coffea ESTs are a valuable resource for microsatellite mining. EST-SSR markers developed from C. canephora sequences can be easily transferred to other Coffea species for which very little molecular information is available. They constitute a set of conserved orthologous markers, which would be ideal for assessing genetic diversity in coffee trees as well as for cross-referencing transcribed sequences in comparative genomics studies.     

Development of EST-SSR markers and their utility in revealing cryptic diversity in safflower (Carthamus tinctorius L.)

With the aim of developing additional genomic resources in safflower, a set of 41,011 ESTs of safflower were mined for the presence of SSRs. 18,773 SSR containing ESTs (SSR-ESTs) were identified and were analyzed to remove redundant sequences leading to identification of 8,810 non-redundant SSR-ESTs (categorized into 6104 singletons and 2,706 contigs) having 13,085 non-redundant SSRs. The average number of non-redundant SSRs per EST was 0.32 and they predominantly consisted of dinucleotide (57.7 %), and trinucleotide (37.7 %) repeat motifs. 500 primer pairs were designed for the non-redundant EST-SSRs of which, 151 were tested. 60 markers which gave robust amplicons, were validated in a set of 19 Carthamus lines. A subset of EST-SSR markers, having average polymorphism information content (PIC) ≥0.4 could precisely elucidate the pedigree relatedness among these lines. Further, these markers exhibited high cross-species transferability to five other wild species of Carthamus. The markers reported here would be a valuable addition to existing safflower marker resources aiding in hastening its improvement.     

Development of SSR markers for the phylogenetic analysis of almond trees from China and the Mediterranean region.

Expressed sequence tag (EST) derived simple sequence repeats (SSRs, microsatellites) were screened and identified from 3863 almond and 10 185 peach EST sequences, and the spectra of SSRs in the non-redundant EST sequences were investigated after sequence assembly. One hundred seventy-eight (12.07%) almond SSRs and 497 (9.97%) peach SSRs were detected. The EST-SSR occurs every 4.97 kb in almond ESTs and 6.57 kb in peach, and SSRs with di- and trinucleotide repeat motifs are the most abundant in both almond and peach ESTs. Twenty one EST-SSRs were thereafter, developed and used together with 7 genomic SSRs, to study the genetic relationship among 36 almond (P. communis Fritsch.) cultivars from China and the Mediterranean area, as well as 8 accessions of other related species from the genus Prunus. Both EST-derived and genomic SSR markers showed high cross-species transferability in the genus. Out of the 112 polymorphic alleles detected in the 36 cultivated almonds, 28 are specific to Chinese cultivars and 25 to the others. The 44 accessions were clustered into 4 groups in the phylogenetic tree and the 36 almond cultivars formed two distinct subgroups, one containing only Chinese cultivars and one of unknown origin and the other only those originating from the Mediterranean area, indicating that Chinese almond cultivars have a distinct evolutionary history from the Mediterranean almond. Our preliminary results indicated that common almond was more closely related to peach (P. persica (L.) Batsch.) than to the four wild species of almond, (P. mongolica Maxim., P. ledebouriana Schleche, P. tangutica Batal., and P. triloba Lindl.). The implications of these SSR markers for evolutionary analysis and molecular mapping of Prunus species are discussed.     

ESMP: A high-throughput computational pipeline for mining SSR markers from ESTs

With the advent of high-throughput sequencing technology, sequences from many genomes are being deposited to public databases at a brisk rate. Open access to large amount of expressed sequence tag (EST) data in the public databases has provided a powerful platform for simple sequence repeat (SSR) development in species where sequence information is not available. SSRs are markers of choice for their high reproducibility, abundant polymorphism and high inter-specific transferability. The mining of SSRs from ESTs requires different high-throughput computational tools that need to be executed individually which are computationally intensive and time consuming. To reduce the time lag and to streamline the cumbersome process of SSR mining from ESTs, we have developed a user-friendly, web-based EST-SSR pipeline "EST-SSR-MARKER PIPELINE (ESMP)". This pipeline integrates EST pre-processing, clustering, assembly and subsequently mining of SSRs from assembled EST sequences. The mining of SSRs from ESTs provides valuable information on the abundance of SSRs in ESTs and will facilitate the development of markers for genetic analysis and related applications such as marker-assisted breeding. AVAILABILITY: The database is available for free at http://bioinfo.aau.ac.in/ESMP.