Analysis of ESTs from multiple Gossypium hirsutum tissues and identification of SSRs.

In an effort to expand the Gossypium hirsutum L. (cotton) expressed sequence tag (EST) database, ESTs representing a variety of tissues and treatments were sequenced. Assembly of these sequences with ESTs already in the EST database (dbEST, GenBank) identified 9675 cotton sequences not present in GenBank. Statistical analysis of a subset of these ESTs identified genes likely differentially expressed in stems, cotyledons, and drought-stressed tissues. Annotation of the differentially expressed cDNAs tentatively identified genes involved in lignin metabolism, starch biosynthesis and stress response, consistent with pathways likely to be active in the tissues under investigation. Simple sequence repeats (SSRs) were identified among these ESTs, and an inexpensive method was developed to screen genomic DNA for the presence of these SSRs. At least 69 SSRs potentially useful in mapping were identified. Selected amplified SSRs were isolated and sequenced. The sequences corresponded to the EST containing the SSRs, confirming that these SSRs will potentially map the gene represented by the EST. The ESTs containing SSRs were annotated to help identify the genes that may be mapped using these markers.     

Genetic mapping of EST-derived microsatellites from the diploid<Emphasis Type="Italic"> Gossypium arboreum</Emphasis> in allotetraploid cotton

To increase the numbers of microsatellites available for use in constructing a genetic map, and facilitate the use of functional genomics to elucidate fiber development and breeding in cotton, we sampled microsatellite sequences from expressed sequence tags (ESTs) transcribed during fiber elongation in the A-genome species Gossypium arboreum to evaluate their frequency of occurrence, level of polymorphism and distribution in the At and Dt subgenomes of tetraploid cotton. From among ESTs derived from G. arboreum fibers at 7–10 days post anthesis (dpa), 931 ESTs were found to contain simple sequence repeats (SSRs); 544 (58.4%) EST-SSR primer pairs were developed, and 468 (86%) amplified PCR products from allotetraploid cotton ( G. hirsutum cv. TM-1 and G. barbadense cv. Hai7124). However, only 99 (18.2%) of these were found to be polymorphic and segregating in our interspecific BC₁ mapping population [(TM-1×Hai7124)×TM-1]. In these amplified and informative EST-SSRs, hexa- and tri-nucleotide repeat motifs were the most frequent, representing 40.1 and 30%, respectively, of the total. A total of 111 loci detected with these 99 EST-SSRs were integrated into our backbone map including 511 SSR loci. The distribution of the EST-SSRs appeared to be non-random, since 72 loci were anchored to the At and 37 to the Dt subgenome of allotetraploid cotton based on linkage tests. Interestingly, out of the 10 pairs of duplicate loci amplified, seven were mapped to the corresponding homeologous linkage groups and/or chromosomes. BLASTX analysis revealed that 69 of the 99 ESTs showed significant similarities to known genes. Some genes important for fiber development, such as sucrose synthase, were mapped to corresponding chromosomes. These EST-SSRs provide structural and functional genomic information that will be useful for understanding cotton fiber development.Communicated by R. Hagemann     

基于陆地棉茎尖转录组序列的genic-SSR标记的开发与评价

利用软件MISA和SSR Locator 对陆地棉（Gossypium hirsutum L.）Coker312茎尖转录组测序得到的73515条Unigene序列进行分析,查找到4507个SSR位点,分布于4039条转录本序列中,SSR出现频率为5.5%,非编码区的SSR位点要显著高于编码区（2853/1654）。SSR重复基元中,三核苷酸重复基元占主导地位（51.03%）,且AAG/CTT （20.08%）类型最多;其次是二核苷酸重复基元（28.76%）,主要为AG/CT（55.47%）。利用引物批量设计软件共开发1569对SSR引物,在陆地棉TM-1、海岛棉3-79 (G. barbadense L.)、阿非利加棉(G. herbaceum L.)、雷蒙德氏棉(G. raimondii Ulbrich.)四个棉种中进行初步评价,其中1117对引物能在四个棉种间扩增出稳定的条带,扩增率为71.2%。选择650对能稳定扩增出条带的引物,在涉及5个棉种（增加了亚洲棉（G. arboreum L.））的13份材料中进一步筛选,83对引物能在13份材料中扩增出特异性条带, PIC变幅在0.121～0.648之间,平均值为0.422,其中80对引物能在7份陆地棉材料中扩增出特异性条带,平均PIC值为0.336;挑选5对在本实验室作图亲本鲁棉研22和鲁原343间有明显多态的引物进行连锁分析,其中4对成功连锁到本实验室构建的遗传图谱上。本研究丰富了棉属genic-SSR的数量,为棉属遗传作图、性状关联分析提供了更多引物选择。     

A combined RFLP-SSR-AFLP map of tetraploid cotton based on a Gossypium hirsutum x Gossypium barbadense backcross population.

An interspecific Gossypium hirsutum x Gossypium barbadense backcross population of 75 BC1 plants was evaluated for 1014 markers. The map consists of 888 loci, including 465 AFLPs, 229 SSRs, 192 RFLPs, and 2 morphological markers, ordered in 37 linkage groups that represent most if not all of the 26 chromosomes, altogether spanning 4400 cM. Loci were not evenly distributed over linkage groups, and 18 of the 26 long groups had a single dense region. This paper proposes a partially revised list of the 13 pairs of homoeologous A/D chromosomes of the 2n = 4x = 52 tetraploid cotton genome. The major revisions, which involve the c3-c17, c4-c22, c5-D08, and c10-c20 homoeologous pairs, are based on the mapping of 68 SSR and RFLP loci with a known chromosome assignment, as well as on comparative alignments with previously published G. hirsutum x G. barbadense maps. The overall congruency in the locus orders and distances of common SSR and RFLP loci in these maps allows for an estimation of the consensus length that reaches a minimum of 5500 cM, and is encouraging for future efforts aimed at developing an integrated map of cultivated cotton. The present map also provides a firm framework for precision mapping of Mendelian components of quantitative traits in cotton     

Isolation, characterisation and mapping of simple sequence repeat loci in potato

Solanum tuberosum L. DNA sequences containing simple sequence repeat (SSR) motifs were extracted from the EMBL database, cDNA and selectively enriched small-insert DNA libraries. Enrichment was achieved using either triplex affinity capture or single-strand hybridisation selection. One hundred and twelve primer pairs which successfully amplified products of the correct size from potato DNA were ultimately designed and synthesised. Ninety-eight of these revealed length polymorphisms in a panel of four diploid and two tetraploid clones, in agreement with the high information content of this class of markers which has been found in other species. All of the markers were assigned a quality score of 1–5 based on their potential usefulness. Eighty-nine loci from 65 of the primer pairs were located on two genetic linkage maps of potato by segregation analysis of the amplified alleles. Fifty-two of the SSRs were clearly single locus. The maps were aligned using 23 SSR primer pairs and 13 RFLP loci mapped in both populations. The markers described constitute a class which should replace Restriction Fragment Length Polymorphisms (RFLP) as the markers of choice for future genetic studies in potato. The sequences of the primers, together with other information on these markers are provided. Received: 12 January 1998 / Accepted: 25 March 1998     

Mapping of 22 expressed sequence tags isolated from a porcine small intestine cDNA library

Complementary DNA sequences were selected from a resource of tentatively identified clones from a porcine small intestine cDNA library. Forty PCR primer pairs were designed to amplify 101–309 base pairs of the 3′ untranslated region of the genes. The PCR conditions were optimized by altering both formamide and magnesium concentrations on samples of pig, mouse, and hamster DNA. Twenty primer pairs that, under stringent conditions, were pig-specific and amplified the expected fragments were chosen for regional assignment in a pig/rodent hybrid cell panel. Furthermore, 22 primer pairs were chosen to amplify DNA from the parental animals of the PiGMaP shared reference families in order to detect possible polymorphisms. Primer pairs that generated polymorphisms were used for genetic mapping. A total of 22 porcine expressed sequence tags (ESTs) were cytogenetically or genetically mapped by this approach. Twelve of the mapped ESTs could be added to the human–porcine comparative map. Received: 8 December 1996 / Accepted: 31 January 1997     

High-density Linkage Map of Cultivated Allotetraploid Cotton Based on SSR, TRAP, SRAP and AFLP Markers

A high-density linkage map was constructed for an F2 population derived from an Interspecific cross of cultivated allotetraploid species between Gossypium hirsutum L. and G. barbadense L. A total of 186 F2 individuals from the Interspecific cross of ＂CRI 36 × Hal 7124＂ were genotyped at I 252 polymorphic loci Including a novel marker system, target region amplification polymorphism （TRAP）. The map consists of 1 097 markers, including 697 simple se- quence repeats （SSRs）, 171 TRAPs, 129 sequence-related amplified polymorphisms, 98 amplified fragment length polymorphisms, and two morphological markers, and spanned 4 536.7 cM with an average genetic distance of 4.1 cM per marker. Using 45 duplicated SSR loci among chromosomes, 11 of the 13 pairs of homologous chromosomes were Identified In tetraploid cotton. This map will provide an essential resource for high resolution mapping of quantitative trait loci and molecular breeding in cotton.     

Genetic and epigenetic status of triple exotic consanguinity cotton introgression lines

Introgression lines are some of the most important germplasm for breeding applications and other research conducted on cotton crops. The DNA methylation level among 10 introgression lines of cotton (Gossypium hirsutum) and three exotic parental species (G. arboreum, G. thurberi and G. barbadense) were assessed by methylation-sensitive amplified polymorphism (MSAP) technology. The methylation level in the introgression lines ranged from 33.3 to 51.5%. However, the lines PD0111 and PD0113 had the lowest methylation level (34.6 and 33.3%, respectively) due to demethylation of most non-coding sequences. Amplified fragment length polymorphism (AFLP) was used to evaluate the genetic polymorphism in the cotton introgression lines. A high degree of polymorphism was observed in all introgression lines (mean 47.2%) based on AFLP and MSAP analyses. This confirmed the effects of genetic improvement on cotton introgression lines. The low methylation varieties, PD0111 and PD0113 (introgression lines), clustered outside of the introgression lines based on MSAP data, which was incongruent with an AFLP-based dendrogram. This phenomenon could be caused by environmental changes or introgression of exotic DNA fragments.     

Development and mapping of EST-derived simple sequence repeat markers for hexaploid wheat.

Expressed sequence tags (ESTs) are a valuable source of molecular markers. To enhance the resolution of an existing linkage map and to identify putative functional polymorphic gene loci in hexaploid wheat (Triticum aestivum L.), over 260,000 ESTs from 5 different grass species were analyzed and 5418 SSR-containing sequences were identified. Using sequence similarity analysis, 156 cross-species superclusters and 138 singletons were used to develop primer pairs, which were then tested on the genomic DNA of barley (Hordeum vulgare), maize (Zea mays), rice (Oryza sativa), and wheat. Three-hundred sixty-eight primer pairs produced PCR amplicons from at least one species and 227 primer pairs amplified DNA from two or more species. EST-SSR sequences containing dinucleotide motifs were significantly more polymorphic (74%) than those containing trinucleotides (56%), and polymorphism was similar for markers in both coding and 5' untranslated (UTR) regions. Out of 112 EST-SSR markers, 90 identified 149 loci that were integrated into a reference wheat genetic map. These loci were distributed on 19 of the 21 wheat chromosomes and were clustered in the distal chromosomal regions. Multiple-loci were detected by 39% of the primer pairs. Of the 90 mapped ESTs, putative functions for 22 were identified using BLASTX queries. In addition, 80 EST-SSR markers (104 loci) were located to chromosomes using nullisomic-tetrasomic lines. The enhanced map from this study provides a basis for comparative mapping using orthologous and PCR-based markers and for identification of expressed genes possibly affecting important traits in wheat.     

An SSR-based genetic linkage map for perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

A simple sequence repeat (SSR)-based linkage map has been constructed for perennial ryegrass (Lolium perenne L.) using a one-way pseudo-testcross reference population. A total of 309 unique perennial ryegrass SSR (LPSSR) primer pairs showing efficient amplification were evaluated for genetic polymorphism, with 31% detecting segregating alleles. Ninety-three loci have been assigned to positions on seven linkage groups. The majority of the mapped loci are derived from cloned sequences containing (CA)_n-type dinucleotide SSR arrays. A small number (7%) of primer pairs amplified fragments that mapped to more than one locus. The SSR locus data has been integrated with selected data for RFLP, AFLP and other loci mapped in the same population to produce a composite map containing 258 loci. The SSR loci cover 54% of the genetic map and show significant clustering around putative centromeric regions. BLASTN and BLASTX analysis of the sequences flanking mapped SSRs indicated that a majority (84%) are derived from non-genic sequences, with a small proportion corresponding to either known repetitive DNA sequence families or predicted genes. The mapped LPSSR loci provide the basis for linkage group assignment across multiple mapping populations.     

Development of transcript-associated microsatellite markers for diversity and linkage mapping studies in hop (<Emphasis Type="Italic">Humulus lupulus</Emphasis> L.)

Data mining of gene sequences available from various projects dealing with the development of expressed sequence tags (ESTs) can contribute to the discovery of new microsatellite markers. Our aim was to develop new microsatellite markers in hop isolated from an enriched cDNA library and from coding GenBank sequences and to test their suitability in hop diversity studies and for construction of a linkage map. In a set of 614 coding GenBank sequences, 72 containing microsatellites were found (11.7%); the most frequent were trinucleotide repeats (54.0%) followed by dinucleotide repeats (34.5%). Additionally, 11 sequences containing microsatellites were isolated from an enriched cDNA library. A total of 34 primer pairs were designed, 29 based on GenBank sequences and five on sequences from the cDNA enriched library. Twenty-seven (79.4%) coding microsatellites were successfully amplified and used in diversity and linkage mapping studies. Eleven primer pairs amplified 12 coding microsatellite loci suitable for mapping and were placed on female and male linkage maps. We were able to extend previous simple sequence repeat (SSR) female, male and integral maps by 38.8, 25.8 and 40.0 cM, respectively. In the diversity study, 36 diverse hop genotypes were analyzed. Twenty-four coding microsatellites were polymorphic, 17 showing co-dominant behavior and 7 primer pairs amplifying three or more bands in some hop genotypes. Altogether, 143 microsatellite DNA fragments were amplified and they revealed a clear separation of hop genotypes according to geographical region, use or breeding history. In addition, a discussion and comparison of results with other plant coding/EST SSR studies is presented. Our results showed that these microsatellite markers can enhance hop diversity and linkage mapping studies and are a comparable marker system to non-coding SSRs.     

四个栽培棉种间的杂种F1细胞遗传学与亲缘关系研究

以棉属四个栽培棉种进行种间杂交,产生(亚洲棉×草棉)和(陆地棉×海岛棉)2个二元杂种F1及其[(亚洲棉×草棉)×(陆地棉×海岛棉)]四元杂种F1,观察和测定4个栽培棉种及其2个二元杂种F1和四元杂种F1的花粉母细胞(PMC)减数分裂的染色体行为及其花粉生活力,以研究4个栽培棉种间的亲缘关系和进化关系。结果表明,二元杂种(亚洲棉×草棉)F1的PMC减数分裂中期Ⅰ出现一个四体环,其余为二价体,染色体构型为2n=26=11Ⅱ 1Ⅳ;花粉生活力的测定表明,(亚洲棉×草棉)F1可育型花粉为50.71%,表现为典型的配子半不育特性,说明两个二倍体棉种间发生一次染色体易位。(陆地棉×海岛棉)F1以26个二价体细胞为主,但有少量的单价体、三价体以及四价体,染色体构型为2n=52=0.78Ⅰ 22.24Ⅱ 0.94Ⅲ 0.98Ⅳ。花粉生活力的测定表明,(陆地棉×海岛棉)F1可育型花粉为54.84%,可见2个四倍体棉种间亲缘关系较近,二者之间仅发生了染色体的易位或倒位。而由4个栽培种合成的四元杂种F1,其减数分裂异常,染色体丢失现象普遍,部分染色体不能联会配对,以单价体的形式存在,并出现三价体、四价体、五价体等多价体,染色体构型为2n=52=5.45Ⅰ 14.41Ⅱ 2.44Ⅲ 1.59Ⅳ 0.63Ⅴ 0.15Ⅵ,其可育花粉为6.87%。研究结果表明了4种栽培棉种之间的亲缘关系相对较近,可以通过遗传重组产生综合有4个栽培棉种性状的新种质。     

Genome-Wide Analysis of the Sus Gene Family in Cotton

Sucrose synthase (Sus) is a key enzyme in plant sucrose metabolism. In cotton, Sus (EC 2.4.1.13) is the main enzyme that degrades sucrose imported into cotton fibers from the phloem of the seed coat. This study demonstrated that the genomes of Gossypium arboreum L., G. raimondii Ulbr., and G. hirsutum L., contained 8, 8, and 15 Sus genes, respectively. Their structural organizations, phylogenetic relationships, and expression profiles were characterized. Comparisons of genomic and coding sequences identified multiple introns, the number and positions of which were highly conserved between diploid and allotetraploid cotton species. Most of the phylogenetic clades contained sequences from all three species, suggesting that the Sus genes of tetraploid G. hirsutum derived from those of its diploid ancestors. One Sus group (Sus I) underwent expansion during cotton evolution. Expression analyses indicated that most Sus genes were differentially expressed in various tissues and had development-dependent expression profiles in cotton fiber cells. Members of the same orthologous group had very similar expression patterns in all three species. These results provide new insights into the evolution of the cotton Sus gene family, and insight into its members' physiological functions during fiber growth and development.     

燕麦EST-SSR标记的开发和利用

为拓展分子标记在燕麦种质资源分析与鉴定中的应用,利用公共数据库中的25376条EST(expressed sequence tags)序列,开展了燕麦EST-SSR功能性标记的开发和利用研究。25376条EST序列经拼接去冗余后获得了11618条序列,从中筛选出含有不同重复基元的SSR且重复次数较多、长度较长的556条EST序列进行引物设计,开发了50对燕麦EST-SSR引物,通过筛选得到40对有效的EST-SSR引物。选取其中4对引物对5个燕麦种质资源进行了PCR扩增及产物测序,结果表明扩增条带多态性是由SSR差异造成的。利用40对ESTSSR引物对15个六倍体燕麦种质资源进行遗传多样性分析,共扩增出89个等位基因,平均每对引物产生2.23个等位基因;UPGMA聚类分析表明,15个六倍体燕麦种质资源在Dice系数为0.93处聚为3支,基本上是按照不同种进行聚类的,在相同种中又根据地理来源分别聚集成支。利用40对EST-SSR引物对31个遗传背景不清的燕麦种质资源进行基因组倍性鉴定,发现这些种质中可能存在有四倍体和二倍体的燕麦新资源。本研究开发的燕麦EST-SSR功能性标记将在燕麦遗传多样性分析、遗传图谱构建及燕麦属内种间基因组鉴定等方面发挥重要作用。     

Multilocus interactions restrict gene introgression in interspecific populations of polyploid Gossypium (cotton)

Abstract.— Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from interspecific hybridization in nature. By applying a detailed restriction fragment length polymorphism (RFLP) map to 3662 BC₃F₂ plants derived from 24 different BC₁ individuals of a cross between Gossypium hirsutum and G. barbadense , large and widespread deficiencies of donor ( G. barbadense ) chromatin were found, and seven independent chromosomal regions were entirely absent. This skewed chromatin transmission is best accounted for by multilocus epistatic interactions affecting chromatin transmission. The observed frequencies of two-locus genotypes were significantly different from Mendelian expectations about 26 times more often than could be explained by chance ( P ≤ 0.01). For identical pairs of loci, different two-locus genotypes occurred in excess in different BC₃ families, implying the existence of higher-order interlocus interactions beyond the resolution of these data. Some G. barbadense markers occurred more frequently than expected by chance, indicating that genomic interactions do not always favor host chromatin. A preponderance of interspecific allelic interactions involved one locus each in the two different subgenomes of (allotetraploid) Gossypium , thus supporting several other lines of evidence suggesting that intersubgenomic interactions contribute to unique features that distinguish tetraploid cotton from its diploid ancestors.