Molecular characterization and genetic mapping of DNA sequences encoding the Type I chlorophyll a/b-binding polypeptide of photosystem I in Lycopersicon esculentum (tomato)

We report the isolation and characterization of a tomato nuclear gene encoding a chlorophyll a/b-binding (CAB) protein of photosystem I (PSI). The coding nucleotide sequence of the gene, designated Cab-6B, is different at eight positions from that of a previously isolated cDNA clone derived from the Cab-6A gene, but the two genes encode identical proteins. Sequence comparison with the cDNA clone revealed the presence of three short introns in Cab-6B. Genetic mapping experiments demonstrate that Cab-6A and Cab-6B are tightly linked and reside on chromosome 5, but the physical distance between the two genes is at least 7 kilobases. Cab-6A and Cab-6B have been designated Type I PSI CAB genes. They are the only two genes of this branch of the CAB gene family in the tomato genome, and they show substantial divergence to the genes encoding CAB polypeptides of photosystem II. The Type I PSI CAB genes, like the genes encoding PSII CAB proteins, are highly expressed in illuminated leaf tissue and to a lesser extent in other green organs.     

Majority of random cDNA clones correspond to single loci in the tomato genome

Summary The number of loci corresponding to each of 34 unique, random cDNA clones has been determined for the diploid plant species Lycopersicon esculentum (tomato) (2n=24). Fifty-three percent of the clones are homologous to loci represented only once in the tomato chromosomes. Thirty-two percent of the clones correspond to two genetically independent loci. The remaining clones belong to gene families represented by 3–5 loci. To determine the number of gene copies per locus, reconstruction experiments were performed on six of the single locus clones. The majority of these loci were estimated to contain only 1 or 2 copies of the gene. These results support the concept that the majority of structural genes in this diploid plant species are arranged in single loci and present in low copy number. Multigene families, such as those for the small subunit of ribulose bisphosphate carboxylase, chlorophyll a/b binding polypeptide and actin are exceptions to this rule.     

Localization in the Tomato Genome of DNA Restriction Fragments Containing Sequences Homologous to the rRNA (45s), the Major Chlorophyll a/b Binding Polypeptide and the Ribulose Bisphosphate Carboxylase Genes

DNA restriction fragments containing sequences homologous to the ribosomal RNA (45s), the major chlorophyll a/b binding polypeptide (CAB) and the small subunit of ribulose bisphosphate carboxylase (RBCS) genes have been localized and mapped in the tomato nuclear genome by linkage analysis. Ribosomal RNA genes map to a single locus, R45s, which resides in a terminal position on the short arm of chromosome 2 and corresponds to the Nucleolar Organizer Region. The size of the 45s repeating unit is estimated to be approximately 9 kb in Lycopersicon esculentum and 11 kb in Lycopersicon pennellii. Five loci were found to contain CAB sequences. Two of the loci, Cab-1 (chromosome 2) and Cab-3 (chromosome 8), together accounted for more than 80% of the hybridization signal. These loci contain more than one CAB structural gene. The other three loci, Cab-2 (chromosome 8), Cab-4 (chromosome 7) and Cab-5 (chromosome 12), each account for <10% of the total signal and may contain only a single copy of the CAB structural sequence. Three loci were found to contain RBCS sequences. Rbcs-2 (chromosome 3) and Rbcs-3 (chromosome 2) were responsible for >80% of the signal, with the remainder being associated with Rbcs-1 (chromosome 2). Rbcs-2 and Rbcs-3 may contain more than one copy of the gene.     

Toward a saturated linkage map in tomato based on isozymes and random cDNA sequences

A linkage map in tomato has been developed based on isozyme and random cDNA clones derived from mRNA. Interspecific backcross and F₂ populations of Lycopersicon esculentum and L. pennellii were employed in the linkage analysis. Allelic differences in cDNA markers were based on restriction fragment length polymorphisms detected through Southern analysis. A total of 57 unique cDNA clones have been analyzed. The majority of cDNA markers correspond to single loci and are dispersed throughtout the genome. Of those clones that hybridize to two or more loci, most show genetic independence (ie., they are unlinked). The combination of isozyme, cDNA and previously mapped DNA markers total 112 loci. It is estimated that approximately 92% of the genome can be monitored during segregation with these markers. Molecular maps, such as the one being constructed in tomato, may allow genetic and breeding experiments that previously were not possible.     

Studies of esterase 6 in Drosophila melanogaster. XVIII. Biochemical differences between the slow and fast allozymes

Most natural populations of Drosophila melanogaster are polymorphic for two major electrophoretic variants at the esterase-6 locus. The frequency of the EST 6F allozyme is greatest in populations in warmer latitudes, whereas the EST 6S allozyme is predominant in colder latitudes. Latitudinal clines in electromorph frequencies are found on three continents. Purified preparations of the allozymes have been characterized for their pH optimum, substrate specificity, organophosphate inhibition, alcohol activation, thermal stability, and kinetic parameters. These and previous analyses of the EST 6 allozymes reveal that the two variants have differences in their physical and kinetic properties that may provide a basis for the selective maintenance of the polymorphisms and an explanation of the clinal variation observed in natural populations.      

High-resolution genetic map of the Lv resistance locus in tomato

 Bulked segregant analysis and high-resolution mapping were used to pinpoint the position of the Lv gene for resistance to Leveillula taurica in tomato. Mapping in an F₂, corresponding to more than 3800 gametes, indicates that Lv is positioned within the 0.84-cM interval defined by the RFLP markers CT121 and CT129, with the closest marker, CT121, being only 0.16 cM from the gene. The tight linkage of these markers demonstrates their usefulness in marker-assisted breeding for Lv, and the high-resolution map provides a starting a starting point for positional cloning of this resistance gene. Received: 25 February 1997 / Accepted: 21 March 1997     

Isozymic gene linkage map of the tomato: Applications in genetics and breeding

Summary New linkage data are presented for the situation of five previously unlocated isozymic loci of the tomato and closely related species with homosequential chromosomes.Prx-1 lies on chromosome 1, where it is also linked withSkdh-1; Aps-2 is linked withGot-4 on chromosome 8;Tpi-2 has been allocated to chromosome 4; and a linkage has been detected betweenPgi-1 andEst-4, whose respective chromosome has not yet been determined. These and previously published data have been summarized in the form of an isozyme linkage map. Twenty-two loci have thus been mapped on nine of the twelve tomato chromosomes. We discuss some new applications of mapped isozymic genes. In certain types of segregations, isozymic genes are far more efficient than morphological markers in providing linkage information. They greatly expedite the cytogenetic investigation of species hybrids and can be utilized to facilitate backcross transfers of genes from wild to cultivated taxa.     

A detailed synteny map of the eggplant genome based on conserved ortholog set II (COSII) markers

We report herein the mapping of 115 PCR-based orthologous markers, including 110 conserved ortholog set or COSII markers, on the reference RFLP map of eggplant. The result permitted inference of a detailed syntenic relationship between the eggplant and tomato genomes. Further, the position of additional 522 COSII markers was inferred in the eggplant map via eggplant-tomato synteny, bringing the total number of markers in the eggplant genome to 869. Since divergence from their last common ancestor approximately 12 million years ago, the eggplant and tomato genomes have become differentiated by a minimum number of 24 inversions and 5 chromosomal translocations, as well as a number of single gene transpositions possibly triggered by transposable elements. Nevertheless, the two genomes share 37 conserved syntenic segments (CSSs) within which gene/marker order is well preserved. The high-resolution COSII synteny map described herein provides a platform for cross-reference of genetic and genomic information (including the tomato genome sequence) between eggplant and tomato and therefore will facilitate both applied and basic research in eggplant. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.