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Query: UMLS:C0027819 (neuroblastoma)
 27,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Co-2 is one of the R-genes against anthracnose identified in common bean. A RAPD marker, cloned as PvH20, was previously shown to contain 6 imperfect leucine-rich-repeats and to reveal a family of related sequences in the vicinity of the Co-2 locus. Using PvH20 as probe, a genomic clone and 2 partial cDNAs were isolated. DNA sequencing revealed that the 6.1 kb genomic fragment contains sequences encoding both NBS-LRR (ORF1) and kinase-like (ORF2) products. The 2 partial cDNAs (cD7 and cD8) belong to the NBS-LRR subfamily as do most of the resistance genes cloned to date. The LRR domain of ORF1 is interrupted by 2 stop codons suggesting that it corresponds to a non-functional member of the multigene family and ORF2 appears to be a kinase pseudogene. The 3 NBS-LRR polypeptides share a high level of amino acid identity and represent different members of a related family. By genetic mapping ORF1, cD7, and cD8 were found to span a genetic distance of 3 cM: cD8 maps at 2 cM from Co-2 and 3 cM from ORF1, cD7 maps at 1 cM from ORF1 and co-segregates with Co-2, thus cD7 might be a putative candidate for the Co-2 R-gene.
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PMID:Cloning and molecular characterization of three members of the NBS-LRR subfamily located in the vicinity of the Co-2 locus for anthracnose resistance in Phaseolus vulgaris. 1023 59

The presence of a single resistance (R) gene allele can determine plant disease resistance. The protein products of such genes may act as receptors that specifically interact with pathogen-derived factors. Most functionally defined R-genes are of the nucleotide binding site-leucine rich repeat (NBS-LRR) supergene family and are present as large multigene families. The specificity of R-gene interactions together with the robustness of plant-pathogen interactions raises the question of their gene number and diversity in the genome. Genomic sequences from tomato showing significant homology to genes conferring race-specific resistance to pathogens were identified by systematically "scanning" the genome using a variety of primer pairs based on ubiquitous NBS motifs. Over 70 sequences were isolated and 10% are putative pseudogenes. Mapping of the amplified sequences on the tomato genetic map revealed their organization as mixed clusters of R-gene homologues that showed in many cases linkage to genetically characterized tomato resistance loci. Interspecific examination within Lycopersicon showed the existence of a null allele. Consideration of the tomato and potato comparative genetic maps unveiled conserved syntenic positions of R-gene homologues. Phylogenetic clustering of R-gene homologues within tomato and other Solanaceae family members was observed but not with R-gene homologues from Arabidopsis thaliana. Our data indicate remarkably rapid evolution of R-gene homologues during diversification of plant families.
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PMID:Comparative genetics of nucleotide binding site-leucine rich repeat resistance gene homologues in the genomes of two dicotyledons: tomato and arabidopsis. 1079 Apr 5

Gene-for-gene plant disease resistance involves two basic processes: perception of pathogen attack, followed by responses to limit disease. Perception involves receptors with high degrees of specificity for pathogen strains, which are encoded by disease resistance genes. Large repertoires of distantly related resistance (R) genes with diverse recognitional specificities are found within a single plant species. The generation of R-gene polymorphism involves gene duplication, followed by DNA-sequence divergence by point mutation, and by deletion and duplication of intragenic DNA repeats encoding blocks of leucine-rich elements. Recombination between related genes reassorts this variation to further diversify gene sequences. Pathogen pressure selects functional resistance specificities and results in the maintenance of R-gene diversity. Recent genome-sequence data reveal that the NBS-LRR (i.e. nucleotide-binding site-leucine-rich repeat) class of R genes represents as much as 1% of the Arabidopsis genome. Experimental data have shown that the LRR has a role in determination of specificity. Mutation experiments, in which R-gene signaling has been dissociated from specificity in constitutive signal mutants, have provided the potential for non-specific resistance to be expressed from pathogen-infection-induced promoters in transgenic plants.
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PMID:Structure, function and evolution of plant disease resistance genes. 1087 44

Plant resistance genes (R genes), especially the nucleotide binding site leucine-rich repeat (NBS-LRR) family of sequences, have been extensively studied in terms of structural organization, sequence evolution and genome distribution. These studies indicate that NBS-LRR sequences can be split into two related groups that have distinct amino-acid motif organizations, evolutionary histories and signal transduction pathways. One NBS-LRR group, characterized by the presence of a Toll/interleukin receptor domain at the amino-terminal end, seems to be absent from the Poaceae. Phylogenetic analysis suggests that a small number of NBS-LRR sequences existed among ancient Angiosperms and that these ancestral sequences diversified after the separation into distinct taxonomic families. There are probably hundreds, perhaps thousands, of NBS-LRR sequences and other types of R gene-like sequences within a typical plant genome. These sequences frequently reside in 'mega-clusters' consisting of smaller clusters with several members each, all localized within a few million base pairs of one another. The organization of R-gene clusters highlights a tension between diversifying and conservative selection that may be relevant to gene families that are unrelated to disease resistance.
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PMID:The genetic architecture of resistance. 1087 48

This article reviews recent advances that shed light on plant disease resistance genes, beginning with a brief overview of their structure, followed by their genomic organization and evolution. Plant disease resistance genes have been exhaustively investigated in terms of their structural organization, sequence evolution and genome distribution. There are probably hundreds of NBS-LRR sequences and other types of R-gene-like sequences within a typical plant genome. Recent studies revealed positive selection and selective maintenance of variation in plant resistance and defence-related genes. Plant resistance genes are highly polymorphic and have diverse recognition specificities. R-genes occur as members of clustered gene families that have evolved through duplication and diversification. These genes appear to evolve more rapidly than other regions of the genome, and domains such as the leucine-rich repeat, are subject to adaptive selection
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PMID:Structure and evolution of plant disease resistance genes. 1244 26

Nucleotide Binding Site/Leucine-Rich Repeat (NBS-LRR) and Serine/Threonine Kinase (STK) genes are two of the known classes of resistance (R-) genes in plants, and occur in large multigene families. Systematic identification of genes for NBS-LRRs and STKs provides a means of access to genomic regions that may be involved in disease resistance. Here we present a picture of these two families of R-gene analogs (RGAs) in grape with the aim of developing a set of resistance-related sequence-tagged-site (STS) markers. One hundred and three NBS-LRR sequences were isolated. They included members of the CC (coiled-coil) and TIR (Toll-interleukin receptor) sub-classes. A comparative analysis with other angiosperm NBSs is provided. Fifty-three genes for receptor-like kinases (RLKs) with serine/threonine specificity were identified. RLK sequences formed a putative monophyletic group within the kinase superfamily. They were similar to both cytoplasmic RLKs, such as Pto, and RLKs with LRR, S-locus, lectin-like and thaumatin-like extracellular binding-domains. The latter resembled the products of the R-related genes Xa21, FLS2, Rlk10, SFR2, and PR5K. Forty-five reference RGAs were converted into STSs by using appropriately designed specific primers. RGA-STSs were present in diverse grape genotypes, and >85% of the primers were capable of amplifying the STSs across the taxa Vitis and Muscadinia. DNA sequence polymorphism among these RGAs was assessed by SSCP (single-strand conformation polymorphism) analysis in over 20 Vitis spp. Finally, 45 universal primers for grape RGAs are proposed that should permit tagging of R-related regions in any grape genome.
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PMID:Nucleotide binding site/leucine-rich repeats, Pto-like and receptor-like kinases related to disease resistance in grapevine. 1288 9

Plant resistance to many types of pathogens and pests can be achieved by the presence of disease resistance (R) genes. The nucleotide binding site-leucine rich repeat (NBS-LRR) class of R-genes is the most commonly isolated class of R-genes and makes up a super-family, which is often arranged in the genome as large multi-gene clusters. The NBS domain of these genes can be targeted by polymerase chain reaction (PCR) amplification using degenerate primers. Previous studies have used PCR derived NBS sequences to investigate both ancient R-gene evolution and recent evolution within specific plant families. However, comparative studies with the Asteraceae family have largely been ignored. In this study, we address recent evolution of NBS sequences within the Asteraceae and extend the comparison to the Arabidopsis thaliana genome. Using multiple sets of primers, NBS fragments were amplified from genomic DNA of three species from the family Asteraceae: Helianthus annuus (sunflower), Lactuca sativa (lettuce), and Cichorium intybus (chicory). Analysis suggests that Asteraceae species share distinct families of R-genes, composed of genes related to both coiled-coil (CC) and toll-interleukin-receptor homology (TIR) domain containing NBS-LRR R-genes. Between the most closely related species, (lettuce and chicory) a striking similarity of CC subfamily composition was identified, while sunflower showed less similarity in structure. These sequences were also compared to the A. thaliana genome. Asteraceae NBS gene subfamilies appear to be distinct from Arabidopsis gene clades. These data suggest that NBS families in the Asteraceae family are ancient, but also that gene duplication and gene loss events occur and change the composition of these gene subfamilies over time.
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PMID:Comparative analysis of NBS domain sequences of NBS-LRR disease resistance genes from sunflower, lettuce, and chicory. 1501 16

The conserved sequences in the nucleotide-binding sites of the nucleotide-binding site-leucine-rich repeat (NBS-LRR) class of disease resistance (R) genes have been used for PCR-based R-gene isolation and subsequent development of molecular markers. Here we present a PCR-based approach (NBS profiling) that efficiently targets R genes and R-gene analogs (RGAs) and, at the same time, produces polymorphic markers in these genes. In NBS profiling, genomic DNA is digested with a restriction enzyme, and an NBS-specific (degenerate) primer is used in a PCR reaction towards an adapter linked to the resulting DNA fragments. The NBS profiling protocol generates a reproducible polymorphic multilocus marker profile on a sequencing gel that is highly enriched for R genes and RGAs. NBS profiling was successfully used in potato with several restriction enzymes, and several primers targeted to different conserved motifs in the NBS. Across primers and enzymes, the NBS profiles contained 50-90% fragments that were significantly similar to known R-gene and RGA sequences. The protocol was similarly successful in other crops (including tomato, barley, and lettuce) without modifications. NBS profiling can thus be used to produce markers tightly linked to R genes and R-gene clusters for genomic mapping and positional cloning and to mine for new alleles and new sources of disease resistance in available germplasm.
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PMID:Efficient targeting of plant disease resistance loci using NBS profiling. 1505 19

The generation of splice variants has been reported for various plant resistance (R) genes, suggesting that these variants play an important role in disease resistance. Most of the time these R genes belong to the Toll and mammalian IL-1 receptor-nucleotide-binding site-leucine-rich repeat (TIR-NBS-LRR) class of R genes. In Phaseolus vulgaris, a resistance gene cluster (referred to as the B4 R-gene cluster) has been identified at the end of linkage group B4. At this complex resistance cluster, three R specificities (Co-9, Co-y and Co-z) and two R QTLs effective against the fungal pathogen Colletotrichum lindemuthianum, the causal agent of anthracnose, have been identified. At the molecular level, four resistance gene candidates encoding putative full-length, coiled-coil (CC)-NBS-LRR R-like proteins, with LRR numbers ranging from 18 to 20, have been previously characterized. In the present study, seven cDNA corresponding to truncated R-like transcripts, belonging to the CC-NBS-LRR class of plant disease R genes, have been identified. These seven transcripts correspond to a single gene named JA1tr, which encodes, at most, only five LRRs. The seven JA1tr transcript variants result from distinct post-transcriptional modifications of JA1tr, corresponding to alternative splicing events of two introns, exon skipping and multiple 'aberrant splicing' events in the open reading frame (ORF). JA1tr was mapped at the B4 R-gene cluster identified in common bean. These post-transcriptional modifications of the single gene JA1tr could constitute an efficient source of diversity. The present results provide one of the few reports of transcript variants with truncated ORFs resulting from a CC-NBS-LRR gene.
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PMID:Distinct post-transcriptional modifications result into seven alternative transcripts of the CC-NBS-LRR gene JA1tr of Phaseolus vulgaris. 1566 Feb 37

Plant disease resistance is the consequence of an innate defense mechanism mediated by Resistance (R) genes [1]. The conserved structure of one class of R protein is reminiscent of Toll-like receptors (TLRs) and Nucleotide binding oligomerization domain (NOD) proteins-immune-response perception modules in animal cells [2, 3, and 4]. The Arabidopsis snc1 (suppressor of npr1-1, constitutive, 1) mutant contains a mutation in a TIR-NBS-LRR-type of R gene that renders resistance responses constitutively active without interaction with pathogens [5]. Few components of the downstream signaling network activated by snc1 are known. To search for regulators of R-gene-mediated resistance, we screened for genetic suppressors of snc1. Three alleles of the mutant mos6 (modifier of snc1, 6) partially suppressed constitutive-resistance responses and immunity to virulent pathogens in snc1. Furthermore, the mos6-1 single mutant exhibited enhanced disease susceptibility to a virulent oomycete pathogen. MOS6, identified by positional cloning, encodes importin alpha3, one of eight alpha importins in Arabidopsis [6]. alpha importins mediate the import of specific proteins across the nuclear envelope. We previously reported that MOS3, a protein homologous to human nucleoporin 96, is required for constitutive resistance in snc1 [7]. Our data highlight an essential role for nucleo-cytoplasmic trafficking, especially protein import, in plant innate immunity.
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PMID:An importin alpha homolog, MOS6, plays an important role in plant innate immunity. 1596 79


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