A bacterial artificial chromosome library for the Chinese alligator (Alligator sinensis)

Chinese alligator (Alligator sinensis) is a rare and endangered species endemic to China. To better understand genetic details of the Chinese alligator genomic structure, a highly redundant bacterial artificial chromosome (BAC) library was constructed. This library consists of 216,238 clones with an average insert size of about 90kb, indicating that the library contains 6.8-fold genome equivalents. Subsequently, we constructed a 516kb contig map for the Chinese alligator olfactory receptor (OR) genes, which spans nine BAC clones, and subjected the BACs to full sequencing. The sequence analysis revealed that this contig contained 16 OR functional genes and meanwhile demonstrated that the nine BACs, which constituted the contig, overlapped correctly, proving the usability of this genome library. As a result, this BAC library could provide a useful platform for physical mapping, genome sequencing or complex analysis of targeted genomic regions for this rare species.     

Physical map and gene survey of the Ochrobactrum anthropi genome using bacterial artificial chromosome contigs

Bacterial artificial chromosome (BAC) clones are effective mapping and sequencing reagents for use with a wide variety of small and large genomes. This report describes research aimed at determining the genome structure of Ochrobactrum anthropi, an opportunistic human pathogen that has potential applications in biodegradation of hazardous organic compounds. A BAC library for O. anthropi was constructed that provides a 70-fold genome coverage based on an estimated genome size of 4.8 Mb. The library contains 3072 clones with an average insert size of 112 kb. High-density colony filters of the library were made, and a physical map of the genome was constructed using a hybridization without replacement strategy. In addition, 1536 BAC clones were fingerprinted with HindIII and analyzed using IMAGE and Fingerprint Contig software (FPC, Sanger Centre, U.K.). The FPC results supported the hybridization data, resulting in the formation of two major contigs representing the two major replicons of the O. anthropi genome. After determining a reduced tiling path, 138 BAC ends from the reduced tile were sequenced for a preliminary gene survey. A search of the public databases with the BLASTX algorithm resulted in 77 strong hits (E-value < 0.001), of which 89% showed similarity to a wide variety of prokaryotic genes. These results provide a contig-based physical map to assist the cloning of important genomic regions and the potential sequencing of the O. anthropi genome.     

Characterization of the genomic organization of the region bordering the centromere of chromosome V of Podospora anserina by direct sequencing

A Podospora anserina BAC library of 4800 clones has been constructed in the vector pBHYG allowing direct selection in fungi. Screening of the BAC collection for centromeric sequences of chromosome V allowed the recovery of clones localized on either sides of the centromere, but no BAC clone was found to contain the centromere. Seven BAC clones containing 322,195 and 156,244bp from either sides of the centromeric region were sequenced and annotated. One 5S rRNA gene, 5 tRNA genes, and 163 putative coding sequences (CDS) were identified. Among these, only six CDS seem specific to P. anserina. The gene density in the centromeric region is approximately one gene every 2.8kb. Extrapolation of this gene density to the whole genome of P. anserina suggests that the genome contains about 11,000 genes. Synteny analyses between P. anserina and Neurospora crassa show that co-linearity extends at the most to a few genes, suggesting rapid genome rearrangements between these two species.     

Construction of a bacterial artificial chromosome library, determination of genome size, and characterization of an Hsp70 gene family in Phytophthora nicotianae

The oomycete plant pathogen Phytophthora nicotianae causes diseases on a wide range of plant species. To facilitate isolation and functional characterization of pathogenicity genes, we have constructed a large-insert bacterial artificial chromosome (BAC) library using nuclear DNA from P. nicotianae H1111. The library contains 10,752 clones with an average insert size of 90 kb and is free of mitochondrial DNA. The quality of the library was verified by hybridization with 37 genes, all of which resulted in the identification of multiple positive clones. The library is estimated to be 10.6 haploid genome equivalents based on hybridization of 23 single-copy genes and the genome size of P. nicotianae was estimated to be 95.5 Mb. Hybridization with a nuclear repetitive DNA probe revealed that 4.4% of clones in the library contained 28S rDNA. Hybridization of total genomic DNA to the library indicated that at least 39% of the BAC library contains repetitive DNA sequences. A BAC pooling strategy was developed for efficient library screening. The library was used to identify and characterize BAC clones containing an Hsp70 gene family whose four members were identified to be clustered within approximately 18 kb in the P. nicotianae genome based on the physical mapping of eight BACs spanning a genomic region of approximately 186 kb. The BAC library created provides an invaluable resource for the isolation of P. nicotianae genes and for comparative genomics studies.     

Construction of a 1.2-Mb contig including the citrus tristeza virus resistance gene locus using a bacterial artificial chromosome library of Poncirus trifoliata (L.) Raf.

The citrus tristeza virus resistance gene (Ctv) is a single dominant gene in Poncirus trifoliata, a sexually compatible relative of citrus. To clone this gene, a bacterial artificial chromosome (BAC) library has been constructed from an individual plant that was homozygous for Ctv. This library contains 45,696 clones with an average insert size of 80 kb, corresponding to 9.6 genome equivalents. Screening of the BAC library with five chloroplast DNA probes indicated that 0.58% of the BAC clones contained chloroplast-derived inserts. The chromosome walk across the Ctv locus was initiated using three closely linked genetic markers: C19, AD8, and Z16. The walk has been completed and a contig of ca. 1.2 Mb was constructed. Based on new data, the genetic map in the Ctv region was revised, with Ctv being located between AD8-Z16 and C19 at distances of 1.2 and 0.6 cM, respectively. Utilizing DNA fragments isolated from the contig as RFLP markers, the Ctv locus was further mapped to a region of ca. 300 kb. This contig contains several putative disease-resistance genes similar to the rice Xa21 gene, the tomato Cf-2 gene, and the Arabidopsis thaliana RPS2 gene. This library will therefore allow cloning of Ctv and other putative disease-resistance genes.     

Construction of a BAC library of <Emphasis Type="Italic"> Rosa rugosa </Emphasis>Thunb. and assembly of a contig spanning<Emphasis Type="Italic"> Rdr1</Emphasis>, a gene that confers resistance to blackspot

A BAC library to serve as a general tool for the physical mapping and positional cloning of rose genes has been constructed from Rosa rugosa DNA. With 27,264 clones the library contains 5.2 genome equivalents. The library was used to assemble a contig of BAC clones spanning Rdr1, a locus that confers resistance to blackspot. For this purpose fine-scale mapping of the target locus was achieved by bulked segregant analysis using 816 AFLP primer combinations. The target region around Rdr1 comprises about 400 kb and is covered by a minimum of six BAC clones. Furthermore, the detection of at least five resistance gene analogs of the TIR-NBS-LRR family on the contig indicates the presence of a cluster of resistance genes around Rdr1. These results will not only allow the isolation and identification of Rdr1 in the near future, but also provide the tools for the physical mapping and positional cloning of other horticulturally interesting genes in roses.     

Construction, characterization and FISH mapping of a bacterial artificial chromosome library of Chinese pangolin (Manis pentadactyla)

Chinese pangolins as a representative species in the order Pholidota have highly specified morphological characters and occupy an important place in the mammalian phylogenetic tree. To obtain genomic data for this species, we have constructed a bacterial artificial chromosome (BAC) library of Chinese pangolin. The library contains 208,272 clones with an average insert size of 122.1 kb and represents approximately eight times the Chinese pangolin haploid genome (if we assume that the Chinese pangolins have a genome size similar to human). One hundred and twenty randomly-selected BAC clones were mapped onto Chinese pangolin chromosomes by fluorescence in situ hybridization (FISH), showing a largely unbiased chromosomal distribution. Several clones containing repetitive DNA and ribosomal DNA genes were also found. The BAC library and FISH mapped BAC clones are useful resources for comparative genomics and cytogenetics of mammals and in particular, the ongoing genome sequencing project of Chinese pangolins.     

Construction of a Coix BAC library and isolation of the 22 kDa &alpha;-coixin gene cluster

Coix lacryma-jobi L. (Coix) is a close relative of maize and is considered a valuable genetic resource for crop improvement. Here we report the construction of the first Coix bacterial artificial chromosome (BAC) library using accession PI 324059. This BAC library contains about 230?400 clones with an average insert size of 113?kb, has low organellar DNA contamination, and provides 16.3-fold coverage of the genome. The library was stored in 12?× 96 pools that could be screened with a PCR protocol. Library screening was performed for the 22?kDa α-coixin gene family. A total of 57 positive pools were identified, and single clones were isolated from 19 of these pools. Based on DNA fingerprinting and Southern blot analysis, these 19 BAC clones form a single contig of about 340?kb in length, indicating that the 22 kDa α-coixin genes occur in a cluster. These results demonstrated the suitability of this BAC library for gene isolation and comparative genomics studies of the Coix genome.     

Korean BAC library construction and characterization of HLA-DRA, HLA-DRB3

A human bacterial artificial chromosome (BAC) library was constructed with high molecular weight DNA extracted from the blood of a male Korean. This Korean BAC library contains 100,224 clones of insert size ranging from 70 to 150 kb, with an average size of 86 kb, corresponding to a 2.9-fold redundancy of the genome. The average insert size was determined from 288 randomly selected BAC clones that were well distributed among all the chromosomes. We developed a pooling system and three-step PCR screen for the Korean BAC library to isolate desired BAC clones, and we confirmed its utility using primer pairs designed for one of the clones. The Korean BAC library and screening pools will allow PCR-based screening of the Korean genome for any gene of interest. We also determined the allele types of HLA-DRA and HLA-DRB3 of clone KB55453, located in the HLA class II region on chromosome 6p21.3. The HLA-DRA and DRB3 genes in this clone were identified as the DRA*010202 and DRB3*01010201 types, respectively. The haplotype found in this library will provide useful information in future human disease studies.     

Direct targeting and rapid isolation of BAC clones spanning a defined chromosome region

To isolate genes of interest in plants, it is essential to construct bacterial artificial chromosome (BAC) libraries from specific genotypes. Construction and organisation of BAC libraries is laborious and costly, especially from organisms with large and complex genomes. In the present study, we developed the pooled BAC library strategy that allows rapid and low cost generation and screening of genomic libraries from any genotype of interest. The BAC library is constructed, directly organised into a few pools and screened for BAC clones of interest using PCR and hybridisation steps, without requiring organization into individual clones. As a proof of concept, a pooled BAC library of approximately 177,000 recombinant clones has been constructed from the barley cultivar Cebada Capa that carries the Rph7 leaf rust resistance gene. The library has an average insert size of 140 kb, a coverage of six barley genome equivalents and is organised in 138 pools of about 1,300 clones each. We rapidly established a single contig of six BAC clones spanning 230 kb at the Rph7 locus on chromosome 3HS. The described low-cost cloning strategy is fast and will greatly facilitate direct targeting of genes and large-scale intra- and inter-species comparative genome analysis.Edwige Isidore and Beatrice Scherrer contributed equally to the work.     

Construction of a BAC library for Chinese amphioxus Branchiostoma belcheri and identification of clones containing Amphi-Pax genes

Amphioxus is a crucial organism for the study of vertebrate evolution. Although a genomic BAC library of Branchiostoma floridae has been constructed, we report here another BAC library construction of its distant relative species Branchiostoma belcheri. The amphioxus BAC library established in present study consists of 45,312 clones arrayed in one hundred and eighteen 384-well plates. The average insert fragment size was 120 kb estimated by Pulsed Field Gel Electrophoresis (PFGE) analysis of 318 randomly selected clones. The representation of the library is about 12 equivalent to the genome, allowing a 99.9995% probability of recovering any specific sequence of interest. We further screened the library with 4 single copied Amphi-Pax genes and identified total of 26 positive clones with average of 6.5 clones for each gene. The result indicates this library is well suited for many applications and should also serve as a useful complemental resource for the scientific community.     

A genomic BAC library and a new BAC-GFP vector to study the holocentric pest Spodoptera frugiperda

Two genomic tools for the study of Lepidoptera and the holocentric structure of their chromosomes are presented in this paper. A bacterial artificial chromosome (BAC) library was constructed using nuclear DNA partially digested with HindIII from eggs of Spodoptera frugiperda. The library contains a total of 36,864 clones with an average insert size of 125 kb, which corresponds to approximately 11.5 genome equivalents. Hybridization screening of the library was performed with eight single-copy genes, giving an average hit of 10 clones per marker gene. Colinearity between the genome and BACs was demonstrated at the triose phosphate isomerase (tpi) locus. Probing of the library with a PCR fragment internal to the 18S ribosomal gene allowed an estimation of the rDNA locus size close to 115 repeats per haploid genome. A new vector (pBAC3.6eGFP) for transient transfection into S. frugiperda cell lines has been constructed. It is based on the BAC vector, pBAC3.6e, in which a gene encoding GFP was inserted under the control of the densovirus P9 promoter. This vector has the advantage to accommodate large genomic inserts and to be transfected in a large lepidopteran host range. It was used to construct a second BAC library from Sf9 cell nuclear DNA in order to allow a comparison between somatic and cell line genome organization.     

Construction and characterization of a sheep BAC library of three genome equivalents

A sheep BAC library of over three genome equivalents was constructed and arrayed in superpools and row, column, and plate pools. The library contains 90,000 clones distributed in 39 superpools. The average insert size was estimated at 123 kb. The library was screened by PCR with 77 primer pairs corresponding to ovine microsatellites distributed throughout the genome. The probability of finding a random sequence in the library could be estimated at 0.96. Received: 2 November 1998 / Accepted: 29 January 1999     

Construction and partial characterization of a Corynebacterium pseudotuberculosis bacterial artificial chromosome library through genomic survey sequencing

Corynebacterium pseudotuberculosis is a gram-positive bacterium that causes caseous lymphadenitis in sheep and goats. However, despite the economic losses caused by caseous lymphadenitis, there is little information about the molecular mechanisms of pathogenesis of this bacterium. Genomic libraries constructed in bacterial artificial chromosome (BAC) vectors have become the method of choice for clone development in high-throughput genomic-sequencing projects. Large-insert DNA libraries are useful for isolation and characterization of important genomic regions and genes. In order to identify targets that might be useful for genome sequencing, we constructed a C. pseudotuberculosis BAC library in the vector pBeloBAC11. This library contains about 18,000 BAC clones, with inserts ranging in size from 25 to 120 kb, theoretically representing a 390-fold coverage of the C. pseudotuberculosis genome (estimated to be 2.5-3.1 Mb). Many genomic survey sequences (GSSs) with homology to C. diphtheriae, C. glutamicum, C. efficiens, and C. jeikeium proteins were observed within a sample of 215 sequenced clones, confirming their close phylogenetic relationship. Computer analyses of GSSs did not detect chimeric, deleted, or rearranged BAC clones, showing that this library has low redundancy. This GSSs collection is now available for further genetic and physical analysis of the C. pseudotuberculosis genome. The GSS strategy that we used to develop our library proved to be efficient for the identification of genes and will be an important tool for mapping, assembly, comparative, and functional genomic studies in a C. pseudotuberculosis genome sequencing project that will begin this year.     

Physical mapping across an avirulence locus of Phytophthora infestans using a highly representative, large-insert bacterial artificial chromosome library

The oomycete plant pathogen Phytophthora infestans is the causal agent of late blight, one of the most devastating diseases of potato worldwide. As part of efforts to clone avirulence (Avr) genes and pathogenicity factors from P. infestans, we have constructed a bacterial artificial chromosome (BAC) library from an isolate containing six Avr genes. The BAC library comprises clones with an average insert size of 98 kb and represents an estimated 10 genome equivalents. A three-dimensional pooling strategy was developed to screen the BAC library for amplified fragment length polymorphism (AFLP) markers, as this type of marker has been extensively used in construction of a P. infestans genetic map. Multiple positive clones were identified for each AFLP marker tested. The pools were used to construct a contig of 11 BAC clones in a region of the P. infestans genome containing a cluster of three avirulence genes. The BAC contig is predicted to encompass the Avr11 locus but mapping of the BAC ends will be required to determine if the Avr3 and Avr10 loci are also present in the BAC contig. These results are an important step towards the positional cloning of avirulence genes from P. infestans, and the BAC library represents a valuable resource for largescale studies of oomycete genome organisation and gene content.     

A bacterial artificial chromosome (BAC) library of Malus floribunda 821 and contig construction for positional cloning of the apple scab resistance gene Vf.

The apple scab resistance gene Vf, originating from the wild species Malus floribunda 821, has been incorporated into a wide variety of apple cultivars through a classical breeding program. With the aim of isolating the Vf gene, a bacterial artificial chromosome (BAC) library consisting of 31 584 clones has been constructed from M. floribunda 821. From the analysis of 88 randomly selected BAC clones, the average insert size is estimated at 125 kb. If it is assumed that the genome size of M. floribunda 821 is 769 Mb/haploid, the library represents about 5x haploid genome equivalents. This provides a 99% probability of finding any specific sequence from this library. PCR-based screening of the library has been carried out using eight random genomic sequence-characterized amplified regions (SCARs), chloroplast- and mitochondria-specific SCARs, and 13 high-density Vf-linked SCAR markers. An average of five positive BAC clones per random SCAR has been obtained, whereas less than 1% of BAC clones are derived from the chloroplast or mitochondrial genomes. Most BAC clones identified with Vf-linked SCAR markers are physically linked. Three BAC contigs along the Vf region have been obtained by assembling physically linked BAC clones based on their fingerprints. The overlapping relatedness of BAC clones has been further confirmed by cytogenetic mapping using fiber fluorescence in situ hybridization (fiber-FISH). The M. floribunda 821 BAC library provides a valuable genetic resource not only for map-based cloning of the Vf gene, but also for finding many other important genes for improving the cultivated apple.     

Construction and characterization of a bacterial artificial chromosome library ofArabidopsis thaliana

We constructed an ordered 3,948-clone arabidopsis BAC library. The library has a combined average insert size of 100 kb (n=54). Assuming a haploid genome size of 100,000 kb, the BAC library contains 3.95 haploid genome equivalents with a 98 percent probability of isolating a specific genomic region. The library was screened with five arabidopsis cDNA probes and one tomato probe; all probes hybridized to at least one (and in most cases three) BAC clones in the library.     

Construction and characterization of a soybean bacterial artificial chromosome library and use of multiple complementary libraries for genome physical mapping

Two plant-transformation-competent large-insert binary clone bacterial artificial chromosome (hereafter BIBAC) libraries were previously constructed for soybean cv. Forrest, using BamHI or HindIII. However, they are not well suited for clone-based genomic sequencing due to their larger ratio of vector to insert size (27.6 kbp:125 kbp). Therefore, we developed a larger-insert bacterial artificial chromosome (BAC) library for the genotype in a smaller vector (pECBAC1), using EcoRI. The BAC library contains 38,400 clones; about 99.1% of the clones have inserts; the average insert size is 157 kbp; and the ratio of vector to insert size is much smaller (7.5 kbp:157 kbp). Colony hybridization with probes derived from several chloroplast and mitochondrial genes showed that 0.89% and 0.45% of the clones were derived from the chloroplast and mitochondrial genomes, respectively. Considering these data, the library represents 5.4 haploid genomes of soybean. The library was hybridized with six RFLP marker probes, 5S rDNA and 18S-5.8S-25S rDNA, respectively. Each RFLP marker hybridized to about six clones, and the 5S and 18S-5.8S-25S rDNA probes collectively hybridized to 402 BACs—about 1.05% of the clones in the library. The BAC library complements the existing soybean Forrest BIBAC libraries by using different restriction enzymes and vector systems. Together, the BAC and BIBAC libraries encompass 13.2 haploid genomes, providing the most comprehensive clone resource for a single soybean genotype for public genome research. We show that the BAC library has enhanced the development of the soybean whole-genome physical map and use of three complementary BAC libraries improves genome physical mapping by fingerprint analysis of most of the clones of the library. The rDNA-containing clones were also fingerprinted to evaluate the feasibility of constructing contig maps of the rDNA regions. It was found that physical maps for the rDNA regions could not be readily constructed by fingerprint analysis, using one or two restriction enzymes. Additional data to fingerprints and/or different fingerprinting methods are needed to build contig maps for such highly tandem repetitive regions and thus, the physical map of the entire soybean genome.     

Construction and application of a bacterial artificial chromosome (BAC) library of<Emphasis Type="Italic"> Prunus armeniaca</Emphasis> L. for the identification of clones linked to the self-incompatibility locus

To facilitate gene discovery in the Rosaceae, a bacterial artificial chromosome (BAC) library was constructed using high-molecular-weight (HMW) DNA from apricot leaves ( Prunus armeniaca L.). The library contains 101,376 clones (264, 384-well plates) with an average insert size of 64 kb, equivalent to 22-fold genome coverage. In the first application of this library, high-density filters were screened for self-incompatibility genes using apricot DNA probes. Eight positive BAC clones were detected and fingerprinted to determine clone relationships and assemble contigs. These results demonstrate the suitability of this library for gene identification and physical mapping of the apricot genome.Communicated by R. Hagemann     

Construction and Identification of Bacterial Artificial Chromosome Library for 0-613-2R in Upland Cotton

A bacterial artificial chromosome （BAC） library containing a large genomlc DNA insert is an important tool for genome physical mapping, map-based cloning, and genome sequencing. To Isolate genes via a map-based cloning strategy and to perform physical mapping of the cotton genome, a high-quality BAC library containing large cotton DNA Inserts Is needed. We have developed a BAC library of the restoring line 0-613-2R for Isolating the fertility restorer （Rf1） gene and genomic research in cotton （Gossypium hirsutum L.）. The BAC library contains 97 825 clones stored In 255 pieces of a 384-well mlcrotiter plate. Random samples of BACs digested with the Notl enzyme Indicated that the average Insert size Is approximately 130 kb, with a range of 80-275 kb, and 95.7% of the BAC clones in the library have an average insert size larger than 100 kb. Based on a cotton genome size of 2 250 Mb, library coverage is 5.7 × haploid genome equivalents. Four clones were selected randomly from the library to determine the stability of the BAC clones. There were no different fingerprints for 0 and 100 generations of each clone digested with Notl and Hlndiii enzymes. Thus, the atabiiity of a single BAC clone can be sustained at iesat for 100 generations. Eight simple sequence repeat （SSR） markers flanking the Rf; gene were chosen to screen the BAC library by pool using PCR method and 25 positive clones were identified with 3.1 positive clones per SSR marker.