Direct sequencing of RAPD fragments using 3'-extended oligonucleotide primers and dye terminator cycle-sequencing.

Random amplified polymorphic DNA (RAPD) markers are used widely to develop high resolution genetic maps and for genome fingerprinting. Typically, single oligomers of approximately 10 nucleotides are used to PCR amplify characteristic RAPD marker fragments. We describe an efficient method for the direct end-sequencing of gel-purified RAPD fragments using one primer from a set of four 3'-terminal extended (A, T, C or G) oligonucleotides, identical to the RAPD primer but for the single nucleotide extension. Strand-specific DNA sequence could be independently read from each of the RAPD fragments without recourse to strand separation or fragment cloning. Informative RAPD fragments could be readily converted into mapped STS or SCAR loci using this technology. The 3'-extended primers may also be used to amplify independent genomic RAPD markers.

Molecular analysis of capsid protein of Homalodisca coagulata Virus-1, a new leafhopper-infecting virus from the glassy-winged sharpshooter, Homalodisca coagulata.

A new virus that infects and causes increased mortality in leafhoppers was isolated from the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae). The virus, named Homalodisca coagulata virus -1, HoCV-1, was associated with increased mortality of cultured 5(th) instar H. coagulata. To identify the presence of H. coagulata viral pathogens, cDNA expression libraries were made from adult and nymphs. Analysis using reverse transcriptase PCR demonstrated that the virus was present in midgut tissues. As the viral capsid proteins are commonly used in classification of newly discovered viruses, the capsid proteins (CP) of the virus discovered in H. coagulata was examined. The order of the polyprotein subunits of HoCV-1 capsid proteins was determined to be CP2, CP4, CP3, and CP1. The CP4/CP3 (AFGL/GKPK) cleavage boundary site was clearly identified when the sequences were aligned. The putative CP3/CP1 (ADVQ/SAFA) cleavage site and the putative CP2/CP4 (VTMQ/EQSA) cleavage site of HoCV-1, respectively, were located in the same region as that of the other viruses. After alignment, the CP3/CP1 cleavage sites and CP2/CP4 cleavage sites of the viruses analyzed fell within 50 amino acids of one another. As with the cricket paralysis virus, HoCV-1 was found to be mainly comprised of beta-sandwiches in CP1-3 with a jelly roll topological motif. CP4 of HoCV-1 appeared to be mainly alpha-helical in structure. CP1-4 domains are most homologous to insect picorna-like virus coat proteins as was demonstrated by the results of the BLASTP and PSI-BLAST tests, and is strongly supported by the structural modeling. While sequence homology between the cricket paralysis virus and HoCV-1 was low, the global structure of the proteins was conserved. Sequence identities were analyzed by in silico comparison to known genes in the public database, NCBI. Phylogenetic analysis performed using the optimized protein alignment generated a phylogram containing 5 clades. Clade 1 consisted of Drosophila C virus, Clade 2 consisted of cricket paralysis virus, Clade 3 of Triatoma virus, Plautia stali intestine virus, Himetobi P virus, black queen cell virus, and HoCV-1. Clade 4 encompassed acute bee paralysis virus and Kashmir bee virus, and Clade 5 consisted of Rhopalosiphum padi virus. Analysis of the capsid protein of this new leafhopper virus provided significant evidence that it is related to other ssRNA insect viruses within the Family, Dicistroviridae. The HoCV-1, capsid protein sequence has been deposited in GenBank, Accession number: DQ308403.

Aphid biology: expressed genes from alate Toxoptera citricida, the brown citrus aphid.

The brown citrus aphid, Toxoptera citricida (Kirkaldy), is considered the primary vector of citrus tristeza virus, a severe pathogen which causes losses to citrus industries worldwide. The alate (winged) form of this aphid can readily fly long distances with the wind, thus spreading citrus tristeza virus in citrus growing regions. To better understand the biology of the brown citrus aphid and the emergence of genes expressed during wing development, we undertook a large-scale 5' end sequencing project of cDNA clones from alate aphids. Similar large-scale expressed sequence tag (EST) sequencing projects from other insects have provided a vehicle for answering biological questions relating to development and physiology. Although there is a growing database in GenBank of ESTs from insects, most are from Drosophila melanogaster and Anopheles gambiae, with relatively few specifically derived from aphids. However, important morphogenetic processes are exclusively associated with piercing-sucking insect development and sap feeding insect metabolism. In this paper, we describe the first public data set of ESTs from the brown citrus aphid, T. citricida. The cDNA library was derived from alate adults due to their significance in spreading viruses (e.g., citrus tristeza virus). Over 5180 cDNA clones were sequenced, resulting in 4263 high-quality ESTs. Contig alignment of these ESTs resulted in 2124 total assembled sequences, including both contiguous sequences and singlets. Approximately 33% of the ESTs currently have no significant match in either the non-redundant protein or nucleic acid databases. Sequences returning matches with an E-value of < or = -10 using BLASTX, BLASTN, or TBLASTX were annotated based on their putative molecular function and biological process using the Gene Ontology classification system. These data will aid research efforts in the identification of important genes within insects, specifically aphids and other sap feeding insects within the Order Hemiptera.

The slick hair coat locus maps to chromosome 20 in Senepol-derived cattle.

The ability to maintain normal temperatures during heat stress is an important attribute for cattle in the subtropics and tropics. Previous studies have shown that Senepol cattle and their crosses with Holstein, Charolais and Angus animals are as heat tolerant as Brahman cattle. This has been attributed to the slick hair coat of Senepol cattle, which is thought to be controlled by a single dominant gene. In this study, a genome scan using a DNA-pooling strategy indicated that the slick locus is most likely on bovine chromosome 20 (BTA20). Interval mapping confirmed the BTA20 assignment and refined the location of the locus. In total, 14 microsatellite markers were individually genotyped in two pedigrees consisting of slick and normal-haired cattle (n = 36), representing both dairy and beef breeds. The maximum LOD score was 9.4 for a 4.4-cM support interval between markers DIK2416 and BM4107. By using additional microsatellite markers in this region, and genotyping in six more pedigrees (n = 86), the slick locus was further localized to the DIK4835 - DIK2930 interval.

Targeted mapping and linkage analysis of morphological isozyme, and RAPD markers in peach.

Nine different F2 families of peach [Prunus persica (L.) Batsch] were analyzed for linkage relationships between 14 morphological and two isozyme loci. Linkage was detected between weeping (We) and white flower (W), 33 cM; double flower (Dl) and pillar (Br), 10 cM; and flesh color (Y) and malate dehydrogenase (Mdh1), 26 cM. A leaf variant phenotypically distinct from the previously reported wavy-leaf (Wa) mutant in peach was found in progeny of 'Davie II'. The new willow-leaf character (designated Wa2) was closely linked (0.4 cM) to a new dwarf phenotype (designated Dw3). Two families derived from the pollen-fertile cultivar 'White Glory' segregated for pollen sterility, but segregation did not follow a 3∶1 ratio. Evidence is presented suggesting that 'White Glory' possesses a pollen-sterility gene (designated Ps2) that is non-allelic to the previously reported pollen-sterility gene (Ps) in peach. Ps2 was linked to both weeping (We-Ps2, 15.5 cM) and white flower (Ps2-W, 25.3 cM). A genomic map of peach containing 83 RAPD, one isozyme, and four morphological markers was generated using an F2 family obtained by selfing an NC174RL x 'Pillar' F1. A total of 83 RAPD markers were assigned to 15 linkage groups. Various RAPD markers were linked to morphological traits. Bulked segregant analysis was used to identify RAPD markers flanking the red-leaf (Gr) and Mdh1 loci in the NC174RL x 'Pillar' and 'Marsun' x 'White Glory' F2 families, respectively. Three markers flanking Mdh1 and ten markers flanking Gr were identified. The combination of RAPD markers and bulked segregant analysis provides an efficient method of identifying markers flanking traits of interest. Markers linked to traits that can only be scored late in development are potentially useful for marker-aided selection in trees. Alternatives for obtaining additional map order information for repulsion-phase markers in large F2 populations are proposed.