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J L Beynon

Publications and source records attributed to J L Beynon.

13 recordsLinked to original sources
PubMed2001

The Arabidopsis downy mildew resistance gene, RPP13-Nd, functions independently of NDR1 and EDS1 and does not require the accumulation of salicylic acid.

RPP13-Nd-mediated resistance prevents parasitism by five isolates of Peronospora parasitica (At) in a transgenic Arabidopsis. Columbia background. We tested the effect of a number of known disease resistance mutations on the RPP13-Nd function and found that resistance remained unaltered in plants carrying mutations in either EDS1 or NDR1 and in double ndr1-1/eds1-2 mutant lines. Furthermore, we found that pbs2, pad4-1, npr1-1, and rps5-1, which compromise resistance to a number of P. parasitica (At) isolates, had no affect on RPP13-Nd function. In addition, RPP13-Nd-mediated resistance remained unchanged in a background of salicylic acid depletion (nahG). We conclude that RPP13-Nd is the first Arabidopsis R gene product reported to act via a novel signaling pathway that is independent of salicylic acid-mediated responses and is completely independent of NDR1 and EDS1.

Arabidopsis↗
PubMed2000

A comparison of Peronospora parasitica (Downy mildew) isolates from Arabidopsis thaliana and Brassica oleracea using amplified fragment length polymorphism and internal transcribed spacer 1 sequence analyses.

Amplified fragment length polymorphism (AFLP) fingerprints and internal transcribed spacer 1 (ITS1) sequences from 27 Peronospora parasitica isolates (collected from Arabidopsis thaliana or Brassica oleracea), 5 Albugo candida isolates (from the same hosts and from Capsella bursa-pastoris), and 1 Bremia lactucae isolate (from Lactuca sativa) were compared. The AFLP analysis divided the isolates into five groups that correlated with taxonomic species and, in most cases, with host origin. The only exception was a group consisting of A. candida isolates from both B. oleracea and C. bursa-pastoris. ITS1 sequence analysis divided the isolates into the same five groups, demonstrated the divergence between P. parasitica isolates from A. thaliana and B. oleracea, and, using previously published ITS1 sequences, clearly showed the relationship between A. candida isolates from different hosts.

Arabidopsis↗
PubMed2000

RPP13 is a simple locus in Arabidopsis thaliana for alleles that specify downy mildew resistance to different avirulence determinants in Peronospora parasitica.

Disease resistance (R) genes are found in plants as either simple (single allelic series) loci, or more frequently as complex loci of tandemly repeated genes. These different loci are likely to be under similar evolutionary forces from pathogens, but the contrast between them suggests important differences in mechanisms associated with DNA structure and recombination that generate and maintain R gene diversity. The RPP13 locus in Arabidopsis represents an important paradigm for studying the evolution of an R gene at a simple locus. The RPP13 allele from the accession Nd-1, designated RPP13-Nd, confers resistance to five different isolates of the biotrophic oomycete, Peronospora parasitica (causal agent of downy mildew), and encodes an NBS-LRR type R protein with a putative amino-terminal leucine zipper. The RPP13-Rld allele, cloned from the accession Rld-2, encodes a different specificity. Comparison of three RPP13 alleles revealed a high rate of amino acid divergence within the LRR domain, less than 80% identity overall, compared to the remainder of the protein (> 95% identity). We also found evidence for positive selection in the LRR domain for amino acid diversification outside the core conserved beta-strand/beta-turn motif, suggesting that more of the LRR structure is available for interaction with target molecules than has previously been reported for other R gene products. Furthermore, an amino acid sequence (LLRVLDL) identical in an LRR among RPP13 alleles is conserved in other LZ NBS-LRR type R proteins, suggesting functional significance.

Alleles↗
PubMed1998

Disease resistance gene homologs correlate with disease resistance loci of Arabidopsis thaliana.

The disease resistance genes RPS2 of Arabidopsis and N of tobacco, among other recently cloned resistance genes, share several conserved sequences. Degenerate oligonucleotide primers, based on conserved sequences in the nucleotide binding site (NBS) and a weak hydrophobic domain of RPS2 and N, were used to amplify homologous sequences from Arabidopsis thaliana. Amplification products were obtained that were similar in sequence to the disease resistance genes RPS2, RPM1, N and L6. The Arabidopsis CIC-YAC library was used to identify the position of the disease resistance homologs on the Arabidopsis genome. Their map positions could be correlated with the disease resistance loci RPS5, RAC1, RPP9, CAR1, RPP7, RPW2, RPP1, RPP10, RPP14, RPP5, RPP4, RPS2, RPW6, HRT, RPS4, RPP8, RPP21, RPP22, RPP23, RPP24 and TTR1. This method was therefore not only successful in the identification of sequences located within gene clusters that are involved in disease resistance, but could also contribute to the cloning of disease resistance genes from Arabidopsis.

Amino Acid Sequence↗
PubMed1998

Identification of R-gene homologous DNA fragments genetically linked to disease resistance loci in Arabidopsis thaliana.

Disease resistance in plants is a desirable economic trait. A number of disease resistance genes from various plant species have been cloned so far. The gene products of some of these can be distinguished by the presence of an N-terminal nucleotide binding site and a C-terminal stretch of leucine-rich repeats. Although these gene products are structurally related, the DNA sequences are poorly conserved. Only parts of the nucleotide binding site share enough DNA identity to design primers for polymerase chain reaction amplification of related DNA sequences. Such primers were used to amplify different resistance-gene-like (RGL) DNA fragments from Arabidopsis thaliana accessions Landsberg erecta and Columbia. Almost all cloned DNA fragments were genetically closely linked with known disease resistance loci. Most RGL fragments were found in a clustered or dispersed multi-copy sequence organization, supporting the supposed correlation of RGL sequences and disease resistance loci.

Amino Acid Sequence↗
PubMed1998

Three genes of the Arabidopsis RPP1 complex resistance locus recognize distinct Peronospora parasitica avirulence determinants.

Plant resistance (R) genes have evolved specific recognition capabilities in defense against pathogens. The evolution of R gene function and maintenance of R gene diversity within a plant species are therefore of great interest. In the Arabidopsis accession Wassilewskija, the RPP1 region on chromosome 3 contains four genetically linked recognition specificities, conditioning resistance to different isolates of the biotrophic oomycete Peronospora parasitica (downy mildew). We show that three of four tightly linked genes in this region, designated RPP1-WsA, RPP1-WsB, and RPP1-WsC, encode functional products of the NBS-LRR (nucleotide binding site-leucine-rich repeat) R protein class. They possess a TIR (Toll, interleukin-1, resistance) domain that is characteristic of certain other NBS-LRR-type R proteins, but in addition, they have unique hydrophilic or hydrophobic N termini. Together, the three RPP1 genes account for the spectrum of resistance previously assigned to the RPP1 region and thus comprise a complex R locus. The distinct but partially overlapping resistance capabilities conferred by these genes are best explained by the hypothesis that each recognizes a different pathogen avirulence determinant. We present evidence suggesting that the RPP genes at this locus are subject to the same selective forces that have been demonstrated for structurally different LRR-type R genes.

Alleles↗
PubMed1989

Is danazol a useful treatment in unexplained primary infertility?

39 patients with primary unexplained infertility were treated in a double-blind placebo-controlled study of danazol. 14 patients completed a treatment course of danazol and 17 of placebo. One patient in the placebo group conceived during the 12 months follow-up period, and none in the danazol group. Danazol does not seem to be an effective treatment for unexplained primary infertility.

Adult↗
PubMed1982

Ethnic differences in perinatal mortality--a challenge.

The perinatal mortality rates of mothers who delivered at St. Thomas's Hospital from 1969 to 1976 have been examined. The rate in the West Indian population was significant higher than in the United Kingdom white population. The increased West Indian mortality was confined to infants with a birth weight of more than 2.0 kg and a gestational age of more than 37 weeks. The relative risk of perinatal death for West Indian mothers compared with UK white mothers was 1.4 at birth weights of 2.5 kg to 2.9 kg, rising to 4.3 at 4.0 + kg. West Indian perinatal mortality in term babies of normal birth weight was higher in all maternal age and parity groups except parity 3, but the difference was greatest in women aged 30 or over. The African perinatal mortality rate was not significantly greater than the UK white rate although it followed the West Indian trends. Pre-eclampsia and forceps delivery were associated with a greatly increased perinatal mortality in West Indian babies. The excess West Indian mortality could not be explained completely by differences in the proportions of stillbirths and early neonatal deaths nor by the distribution of births by parity, maternal age, or social class. Possible explanations for the differences in mortality are discussed.

Birth Weight↗
PubMedDate not supplied

Phenotypic and genotypic variation in the interaction between Arabidopsis thaliana and Albugo candida.

Two biotrophic parasites of the wild crucifer Arabidopsis thaliana (L.) Heynh, are being used to explore the molecular basis and evolution of genotype-spcific recognition and host defense. Genes for recognition of Peronospora parasitica (downy mildew) are numerous in A. thaliana and located on four of the five chromosomes as described previously. Genes for recognition of the closely related parasite Albugo candida (white blister) are described here. In contrast to teh former parasite, less than 15% of the host accessions tested were capable of recognizing either of two isolates of A. candida. The geographic regions represented by these accessions included countries in eastern and western Europe, Asia, North America and Africa. Extensive collections from England and Germany were required to identify examples of incompatible interactions. Phenotypic variation among incompatible interactions included reduced blister formations of complete lack of asexual reproduction by the parasite. Variation in the extent of the host response was also observed. Three host genes for recognition of A. candida (RAC), each associated with different interactions phenotypes, were identified through inheritance studies with three accessions. One of these genes at locus RAC1 appeared to be completely dominant, whereas the other two genes were only partially dominant or recessive under certain conditions, possibly including the effect of genetic background. One of the later two genes defined a second locus RAC2. RAC1 was mapped to the top arm of chromosome 1 in the 1 cM interval between RFLP markers M254 and M253.

Arabidopsis↗