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V M Williamson

Publications and source records attributed to V M Williamson.

At least 19 recordsLinked to original sources
PubMed1998

The nematode resistance gene Mi of tomato confers resistance against the potato aphid.

Resistance against the aphid Macrosiphum euphorbiae previously was observed in tomato and attributed to a novel gene, designated Meu-1, tightly linked to the nematode resistance gene, Mi. Recent cloning of Mi allowed us to determine whether Meu-1 and Mi are the same gene. We show that Mi is expressed in leaves, that aphid resistance is isolate-specific, and that susceptible tomato transformed with Mi is resistant to the same aphid isolates as the original resistant lines. We conclude that Mi and Meu-1 are the same gene and that Mi mediates resistance against both aphids and nematodes, organisms belonging to different phyla. Mi is the first example of a plant resistance gene active against two such distantly related organisms. Furthermore, it is the first isolate-specific insect resistance gene to be cloned and belongs to the nucleotide-binding, leucine-rich repeat family of resistance genes.

Animals↗
PubMed1998

Genetic and physical localization of the root-knot nematode resistance locus mi in tomato.

As part of a map-based cloning strategy designed to isolate the root-knot nematode resistance gene Mi, tomato F2 populations were analyzed in order to identify recombination points close to this economically important gene. A total of 21,089 F2 progeny plants were screened using morphological markers. An additional 1887 F2 were screened using PCR-based flanking markers. Fine-structure mapping of recombinants with newly developed AFLP markers, and RFLP markers derived from physically mapped cosmid subclones, localized Mi to a genomic region of about 550 kb. The low frequency of recombinants indicated that recombination was generally suppressed in these crosses and that crossovers were restricted to particular regions. To circumvent this problem, a population of Lycopersicon peruvianum, the species from which Mi was originally introgressed, that was segregating for resistance was developed. Screening of this population with PCR, RFLP and AFLP markers identified several plants with crossovers near Mi. Recombination frequency was approximately eight-fold higher in the Mi region of the L. peruvianum cross. However, even within the wild species cross, recombination sites were not uniformly distributed in the region. By combining data from the L. esculentum and L. peruvianum recombinant analyses, it was possible to localize Mi to a region of the genome spanning less than 65 kb.

Animals↗
PubMed1998

Characterization of LeMir, a root-knot nematode-induced gene in tomato with an encoded product secreted from the root.

A tomato gene that is induced early after infection of tomato (Lycopersicon esculentum Mill.) with root-knot nematodes (Meloidogyne javanica) encodes a protein with 54% amino acid identity to miraculin, a flavorless protein that causes sour substances to be perceived as sweet. This gene was therefore named LeMir (L. esculentum miraculin). Sequence similarity places the encoded protein in the soybean trypsin-inhibitor family (Kunitz). LeMir mRNA is found in root, hypocotyl, and flower tissues, with the highest expression in the root. Rapid induction of expression upon nematode infection is localized to root tips. In situ hybridization shows that LeMir is expressed constitutively in the root-cap and root-tip epidermis. The LeMir protein product (LeMir) was produced in the yeast Pichia pastoris for generation of antibodies. Western-blot analysis showed that LeMir expression is up-regulated by nematode infection and by wounding. LeMir is also expressed in tomato callus tissue. Immunoprint analysis revealed that LeMir is expressed throughout the seedling root, but that levels are highest at the root/shoot junction. Analysis of seedling root exudates revealed that LeMir is secreted from the root into the surrounding environment, suggesting that it may interact with soil-borne microorganisms.

Amino Acid Sequence↗
PubMed1998

The root knot nematode resistance gene Mi from tomato is a member of the leucine zipper, nucleotide binding, leucine-rich repeat family of plant genes.

The Mi locus of tomato confers resistance to root knot nematodes. Tomato DNA spanning the locus was isolated as bacterial artificial chromosome clones, and 52 kb of contiguous DNA was sequenced. Three open reading frames were identified with similarity to cloned plant disease resistance genes. Two of them, Mi-1.1 and Mi-1.2, appear to be intact genes; the third is a pseudogene. A 4-kb mRNA hybridizing with these genes is present in tomato roots. Complementation studies using cloned copies of Mi-1.1 and Mi-1.2 indicated that Mi-1.2, but not Mi-1.1, is sufficient to confer resistance to a susceptible tomato line with the progeny of transformants segregating for resistance. The cloned gene most similar to Mi-1.2 is Prf, a tomato gene required for resistance to Pseudomonas syringae. Prf and Mi-1.2 share several structural motifs, including a nucleotide binding site and a leucine-rich repeat region, that are characteristic of a family of plant proteins, including several that are required for resistance against viruses, bacteria, fungi, and now, nematodes.

Amino Acid Sequence↗
PubMed1993

Isolation of a tomato alcohol dehydrogenase 2-encoding cDNA using phage-promoted antibody screening of a plasmid cDNA library.

We describe the cloning of a cDNA encoding tomato alcohol dehydrogenase 2 (Adh2) by screening plasmid cDNA clones in phage plaques. A cDNA library constructed in a plasmid vector containing a unique SstI site at the 5' end of the cDNA insert was transferred into the SstI site of the lacZ gene of phage lambda Charon16, and screened by anti-Adh2 antibody to identify reactive plaques. Plasmid cDNA clones were recovered by SstI digestion, ligation, and transformation from phage minipreps for subsequent characterization. This system preserves the original plasmid library for subsequent screening with nucleic acid probes to identify full-length, multiple independent, or related cDNA clones not subject to the selection pressure of phage growth or lysogeny, or negative antibody reactivity. Thirty-two cDNA clones were identified with polyclonal antiserum to Adh2. Three of these reacted with monoclonal anti-Adh2 and only those three hybridized to maize adh1 sequence. One of these cDNAs, Adh31, was further characterized as encoding Adh2 by hybrid-selected translation and high sequence homology with the maize adh1 gene.

Alcohol Dehydrogenase↗
PubMed1992

A spontaneous chromosomal amplification of the ADH2 gene in Saccharomyces cerevisiae.

A spontaneous antimycin A-resistant mutant carrying approximately four extra copies of ADH2 on chromosome XII was isolated from yeast strain 315-1D which lacks a functional copy of ADH1 and thus is antimycin A-sensitive. The additional copies of the normally glucose-repressed ADH2 are expressed during growth on glucose accounting for the antimycin A resistance. These extra copies are inserted into nonadjacent ribosomal DNA sequences (rDNA) near the recombination stimulating sequence HOT1. Each extra copy of the ADH2 gene (1548 bp) replaces most of the 37S transcript (approximately 7400 bp) in one of the approximately 200 copies of the rDNA present in the yeast genome. All four extra copies of ADH2 are lost at a rate of approximately 1 x 10(-5) deletions per cell per generation. One of the joints between the rDNA and ADH2 DNA is located 7 nucleotides downstream from 20 adenine residues in the normal copy of ADH2. This joint occurs at the end of a stretch of 16-29 thymidines in the rDNA which has been expanded to 57-59 thymidines. The other novel joint is located in a short region of sequence similarity between ADH2 and the rDNA. These observations suggest that amplification of ADH2 was a two step process: first the ADH2 gene was inserted into the rDNA, then multiple copies were generated by unequal crossing over or gene conversion within the rDNA.

Alcohol Dehydrogenase↗
PubMed1992

The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes.

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.

Animals↗
PubMed1991

Isolation of Caenorhabditis elegans mutants lacking alcohol dehydrogenase activity.

Alcohol dehydrogenase (ADH) and the genes encoding this enzyme have been studied intensively in a broad range of organisms. Little, however, has been reported on ADH in the free-living nematode Caenorhabditis elegans. Extracts of wild-type C. elegans contain ADH activity and display a single band of activity on a native polyacrylamide gel. Reaction rate for alcohol oxidation is more rapid with higher molecular weight alcohols as substrate than with ethanol. Primary alcohols are preferred to secondary alcohols. C. elegans is sensitive to allyl alcohol, a compound that has been used to select for ADH-null mutants of several organisms. Allyl alcohol-resistant mutant strains were selected from ethylmethanesulfonate (EMS)-mutagenized nematode populations. ADH activity was measured in extracts from eight of these strains and was found to be low or nondetectable. These results form a basis for molecular and genetic characterization of ADH expression in C. elegans.

Alcohol Dehydrogenase↗
PubMed1987

Homology of Saccharomyces cerevisiae ADH4 to an iron-activated alcohol dehydrogenase from Zymomonas mobilis.

Insertion of the transposable element Ty at the ADH4 locus results in increased levels of a new alcohol dehydrogenase (ADH) activity in Saccharomyces cerevisiae. The DNA sequence of this locus has been determined. It contains a long open reading frame which is not homologous to the other ADH isozymes that have been characterized in S. cerevisiae nor does it show obvious homology to Drosophila ADH. The hypothetical ADH does, however, show strong homology to the sequence of an iron-activated ADH from the bacterium Zymomonas mobilis. Thus ADH4 appears to encode an ADH structural gene which, along with the Zymomonas enzyme, may define a new family of alcohol dehydrogenases.

Aeromonas↗
PubMed1986

Resistance to antimycin A in yeast by amplification of ADH4 on a linear, 42 kb palindromic plasmid.

A yeast strain lacking a functional copy of ADH1 has been isolated that is resistant to antimycin A because of the presence of multiple copies of a nuclear gene, ADH4. The amplified copies of ADH4 exist on linear molecules 42 kb in length, which can be separated from chromosomal DNA by orthogonal-field-alternation gel electrophoresis. These amplified molecules are palindromes that reanneal rapidly after denaturation to form linear, snap-back molecules 21 kb in length. The amplified ADH4 sequences are bounded by telomere-homologous sequences. The chromosomal copy of ADH4 is the most distal marker on the left arm of chromosome VII, and the amplified ADH4-containing molecules appear to contain two copies of the region extending from ADH4 to the telomere.

Alcohol Dehydrogenase↗
PubMed1986

Ty insertions at two loci account for most of the spontaneous antimycin A resistance mutations during growth at 15 degrees C of Saccharomyces cerevisiae strains lacking ADH1.

The mutation rate to antimycin A resistance was determined for strains of Sacchromyces cerevisiae lacking a functional copy of the structural gene for alcohol dehydrogenase I (ADH1). One type of mutation that can cause antimycin A resistance in these strains is insertion of the transposable element Ty 5' to ADH2, the structural gene for the glucose-repressed isozyme of alcohol dehydrogenase, resulting in expression of this gene during growth on glucose. Here we show that after growth at 15 or 20 degrees C on glucose, 30% of the antimycin A resistance mutations are Ty insertions at ADH2 and another 65% of the mutations are Ty insertions at ADH4, a new locus identified and cloned as described in this paper. At 30 degrees C only 6% of the mutations are Ty insertions at either of these two loci. In addition, we show that the transposition rate is lower in mating-incompetent (a/alpha) cells than in either haploid or diploid mating-competent cells. Our results suggest that under certain conditions Ty transposition may be a major cause of spontaneous mutations in S. cerevisiae.

Alcohol Dehydrogenase↗
PubMed1983

Nucleotide sequence of the yeast alcohol dehydrogenase II gene.

The complete nucleotide sequence of the glucose-repressed alcohol dehydrogenase II gene (ADR2) from yeast has been established together with its 5'- and 3'-flanking regions. The limits of the gene have been determined by reverse transcriptase sequencing of the 5'-ends and by S1 nuclease mapping of the 3'-ends of the mature ADR2 mRNA. Comparison of the alcohol dehydrogenase I gene (ADC1) sequence (Bennetzen, J. L., and Hall, B.D. (1982) J. Biol. Chem. 257, 3018-3025) with that of ADR2 indicated four regions of sequence conservation in the 5'-flanking DNAs. One of these conserved regions contains the sequence TCAAG which may function as a yeast cap sequence. The coding sequence of ADR2 is 89% homologous with that of ADC1 and exhibits a bias in its codon utilization. Evidence is presented that the intergenic region at the 3'-end of the ADR2 gene is less than 550 base pairs.

Alcohol Dehydrogenase↗
PubMed1983

Characterization of transposable element-associated mutations that alter yeast alcohol dehydrogenase II expression.

Seven cis-dominant, constitutively expressed mutations of the normally glucose-repressible isozyme of alcohol dehydrogenase (ADHII) from the yeast Saccharomyces cerevisiae are caused by insertion of transposable elements from the Ty1 family in front of the ADHII structural gene (ADR2) (V. M. Williamson, E. T. Young, and M. Ciriacy, Cell 23:605-614, 1981). We cloned ADR2 with its associated Ty1 element from five S. cerevisiae strains carrying these mutations. Comparison of the Ty1 elements by heteroduplex studies and restriction enzyme analyses indicated that four were very similar; the fifth, although the same size as the others (about 5.6 kilobases), differed by the presence of two large substitutions of approximately 1 and 2 kilobases. The DNA sequences of the terminal direct repeats (deltas) were very homologous but not identical and were similar to previously reported Ty1 element direct repeats. We determined the 5'-flanking sequences of the ADR2 gene isolated from a wild-type strain and from five Ty1-associated mutations. The 5-base pair target sequence at the site of Ty1 insertion was present at both ends of each Ty1 element. The sites of insertion of the elements were all different and occurred from 125 to 210 base pairs in front of the coding region of ADR2. The 5' end of the major transcript as determined by S1 mapping was the same in wild-type cells and in Ty1-associated constitutive mutants and was approximately 54 base pairs upstream from the coding region. ADR2 transcripts were not detected when a solo delta sequence was present in the 5'-flanking region of this gene.

Alcohol Dehydrogenase↗
PubMed1981

Analysis of mutations affecting Ty-mediated gene expression in Saccharomyces cerevisiae.

Yeast translocatable, Ty, elements can cause constitutive synthesis of the glucose-repressible alcohol dehydrogenase (ADHII) when inserted upstream from the 5' end of the structural gene, ADR2. These insertion mutations, ADR3c, are unstable and give rise to secondary ADHII- mutations. The majority of such mutants, adr3, can be attributed to excision of the insertion sequence, leaving behind a single copy of the delta-sequence which occurs as a direct repeat at the ends of the Ty elements. A few adr3 mutants appear to be generated by DNA-rearrangements in the vicinity of the Ty insertion. The occurrence of recessive mutants, tye, which are unlinked to ADR2 indicates that the constitutive expression of ADR2 caused by the Ty insertions requires the function of trans-acting genes. These results support the idea that regulation of Ty-linked ADR2 is actively mediated by the insertion sequence and is probably not due to a mere disruption of the wild-type controlling site.

Alcohol Oxidoreductases↗