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At least 55 records · Page 3Linked to original sources
PubMed2003

Changes in level of virus accumulation and incidence of infection are critical in the characterization of Rice tungro bacilliform virus (RTBV) resistance in rice.

Analysis by enzyme-linked immunosorbent assay showed that Rice tungro bacilliform virus (RTBV) accumulated in a cyclic pattern from early to late stages of infection in tungro-susceptible variety, Taichung Native 1 (TN1), and resistant variety, Balimau Putih, singly infected with RTBV or co-infected with RTBV + Rice tungro spherical virus (RTSV). These changes in virus accumulation resulted in differences in RTBV levels and incidence of infection. The virus levels were expressed relative to those of the susceptible variety and the incidence of infection was assessed at different weeks after inoculation. At a particular time point, RTBV levels in TN1 or Balimau Putih singly infected with RTBV were not significantly different from the virus level in plants co-infected with RTBV + RTSV. The relative RTBV levels in Balimau Putih either singly infected with RTBV or co-infected with RTBV + RTSV were significantly lower than those in TN1. The incidence of RTBV infection varied at different times in Balimau Putih but not in TN1, and to determine the actual infection, the number of plants that became infected at least once anytime during the 4 wk observation period was considered. Considering the changes in RTBV accumulation, new parameters for analyzing RTBV resistance were established. Based on these parameters, Balimau Putih was characterized having resistance to virus accumulation although the actual incidence of infection was >75%.

Animals↗
PubMed2002

Pyramiding transgenes for multiple resistance in rice against bacterial blight, yellow stem borer and sheath blight.

Here we describe the development of transgene-pyramided stable elite rice lines resistant to disease and insect pests by conventional crossing of two transgenic parental lines transformed independently with different genes. The Xa21 gene (resistance to bacterial blight), the Bt fusion gene (for insect resistance) and the chitinase gene (for tolerance of sheath blight) were combined in a single rice line by reciprocal crossing of two transgenic homozygous IR72 lines. F4 plant lines carrying all the genes of interest stably were identified using molecular methods. The identified lines, when exposed to infection caused by Xanthomonas oryzae pv oryzae, showed resistance to bacterial blight. Neonate larval mortality rates of yellow stem borer ( Scirpophaga incertulas) in an insect bioassay of the same identified lines were 100%. The identified line pyramided with different genes to protect against yield loss showed high tolerance of sheath blight disease caused by Rhizoctonia solani.

Animals↗
PubMed2004

[QTL analysis for lodging resistance in rice using a DH population under lowland and upland ecosystems].

A DH (doubled haploid) population derived from a cross between Japonica upland rice IRAT109 and Japonica paddy rice Yuefu,was used in this study. Three culm traits, basal culm thickness(BCT), culm length (CL) and culm strength (CS), of DH lines and their parents under upland and lowland ecosystems at milk stage were studied. There were very significant positive correlations between BCT and CL, between BCT and CS and between CL and CS. Data from upland and lowland ecosystems were analyzed respectively and jointly, based on a constructed molecular linkage map(including 94 RFLP markers and 71 SSR markers and covering 1 535. 1cM)and the software QTLmapper version 1.0. A total of nine additive QTLs and five pairs of epistatic QTLs associated with BCT, CL, and CS were found by data analysis respectively. Six additive QTLs and six pairs of epistatic QTLs associated with BCT and CL were detected by data analysis jointly. Six additive QTLs and one pair of epistatic QTLs were detected by both methods. Two additive QTLs and two pairs of epistatic QTLs ( bct1a, c/9, c/6a-c/6c and cs5-cs12) for culm traits with general contributions of over 30% to phenotypic variation might be useful for upland rice lodging resistance molecular breeding under upland ecosystem.

Ecosystem↗
PubMed1995

A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21.

The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned Xa21 gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of Xa21 should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.

Amino Acid Sequence↗
PubMed2000

Characterizing rice lesion mimic mutants and identifying a mutant with broad-spectrum resistance to rice blast and bacterial blight.

Many plant mutants develop spontaneous lesions that resemble disease symptoms in the absence of pathogen attack. In several pathosystems, lesion mimic mutations have been shown to be involved in programmed cell death, which in some instances leads to enhanced disease resistance to multiple pathogens. We investigated the relationship between spontaneous cell death and disease resistance in rice with nine mutants with a range of lesion mimic phenotypes. All nine mutations are controlled by recessive genes and some of these mutants have stunted growth and other abnormal characteristics. The lesion mimics that appeared on the leaves of these mutants were caused by cell death as measured by trypan blue staining. Activation of six defense-related genes was observed in most of the mutants when the mimic lesions developed. Four mutants exhibited significant enhanced resistance to rice blast. One of the mutants, spl11, confers non-race-specific resistance not only to blast but also to bacterial blight. The level of resistance in the spl11 mutant to the two pathogens correlates with the defense-related gene expression and lesion development on the leaves. The results suggest that some lesion mimic mutations in rice may be involved in disease resistance, and cloning of these genes may provide a clue to developing broad-spectrum resistance to diverse pathogens.

Bacteria↗
PubMed2004

High-resolution genetic mapping at the Bph15 locus for brown planthopper resistance in rice (Oryza sativa L.).

Resistance to the brown planthopper (BPH), Nilaparvata lugens Stal, a devastating sucking insect pest of rice, is an important breeding objective in rice improvement programs. Bph15, one of the 17 major BPH resistance genes so far identified in both cultivated and wild rice, has been identified in an introgression line, B5, and mapped on chromosome 4 flanked by restriction fragment length polymorphism markers C820 and S11182. In order to pave the way for positional cloning of this gene, we have developed a high-resolution genetic map of Bph15 by positioning 21 DNA markers in the target chromosomal region. Mapping was based on a PCR-based screening of 9,472 F(2) individuals derived from a cross between RI93, a selected recombinant inbred line of B5 bearing the resistance gene Bph15, and a susceptible variety, Taichung Native 1, in order to identify recombinant plants within the Bph15 region. Recombinant F(2) individuals with the Bph15 genotype were determined by phenotype evaluation. Analysis of recombination events in the Bph15 region delimited the gene locus to an interval between markers RG1 and RG2 that co-segregated with the M1 marker. A genomic library of B5 was screened using these markers, and bacterial artificial chromosome clones spanning the Bph15 chromosome region were obtained. An assay of the recombinants using the sub-clones of these clones in combination with sequence analysis delimited the Bph15 gene to a genomic segment of approximately 47 kb. This result should serve as the basis for eventual isolation of the Bph15 resistance gene.

Animals↗
PubMed2004

The rice bacterial blight resistance gene xa5 encodes a novel form of disease resistance.

The rice xa5 gene for disease resistance to Xanthomonas oryzae pv. oryzae has been positionally cloned and encodes the gamma subunit of transcription factor IIA (TFIIAgamma). TFIIAgamma is a general eukaryotic transcription factor with no previously known role in disease resistance. xa5 is unusual in that it is recessive and does not conform to one of the typical resistance gene structural classes. Sequencing of TFIIAgamma in resistant and susceptible isolines revealed two nucleotide substitutions resulting in an amino acid change between resistant and susceptible cultivars. This association was conserved across 27 resistant and nine susceptible rice lines in the Aus-Boro group.

Amino Acid Sequence↗
PubMed2003

Candidate defense genes from rice, barley, and maize and their association with qualitative and quantitative resistance in rice.

Candidate genes involved in both recognition (resistance gene analogs [RGAs]) and general plant defense (putative defense response [DR]) were used as molecular markers to test for association with resistance in rice to blast, bacterial blight (BB), sheath blight, and brown plant-hopper (BPH). The 118 marker loci were either polymerase chain reaction-based RGA markers or restriction fragment length polymorphism (RFLP) markers that included RGAs or putative DR genes from rice, barley, and maize. The markers were placed on an existing RFLP map generated from a mapping population of 116 doubled haploid (DH) lines derived from a cross between an improved indica rice cultivar, IR64, and a traditional japonica cultivar, Azucena. Most of the RGAs and DR genes detected a single locus with variable copy number and mapped on different chromosomes. Clusters of RGAs were observed, most notably on chromosome 11 where many known blast and BB resistance genes and quantitative trait loci (QTL) for blast, BB, sheath blight, and BPH were located. Major resistance genes and QTL for blast and BB resistance located on different chromosomes were associated with several candidate genes. Six putative QTL for BB were located on chromosomes 2, 3, 5, 7, and 8 and nine QTL for BPH resistance were located to chromosomes 3, 4, 6, 11, and 12. The alleles of QTL for BPH resistance were mostly from IR64 and each explained between 11.3 and 20.6% of the phenotypic variance. The alleles for BB resistance were only from the Azucena parent and each explained at least 8.4% of the variation. Several candidate RGA and DR gene markers were associated with QTL from the pathogens and pest. Several RGAs were mapped to BB QTL. Dihydrofolate reductase thymidylate synthase co-localized with two BPH QTL associated with plant response to feeding and also to blast QTL. Blast QTL also were associated with aldose reductase, oxalate oxidase, JAMyb (a jasmonic acid-induced Myb transcription factor), and peroxidase markers. The frame map provides reference points to select candidate genes for cosegregation analysis using other mapping populations, isogenic lines, and mutants.

Aldehyde Reductase↗
PubMed1997

Construction of an 800-kb contig in the near-centromeric region of the rice blast resistance gene Pi-ta2 using a highly representative rice BAC library.

We constructed a rice Bacterial Artificial Chromosome (BAC) library from green leaf protoplasts of the cultivar Shimokita harboring the rice blast resistance gene Pi-ta. The average insert size of 155 kb and the library size of seven genome equivalents make it one of the most comprehensive BAC libraries available, and larger than many plant YAC libraries. The library clones were plated on seven high density membranes of microplate size, enabling efficient colony identification in colony hybridization experiments. Seven percent of clones carried chloroplast DNA. By probing with markers close to the blast resistance genes Pi-ta2(closely linked to Pi-ta) and Pi-b, respectively located in the centromeric region of chromosome 12 and near the telomeric end of chromosome 2, on average 2.2 +/- 1.3 and 8.0 +/- 2.6 BAC clones/marker were isolated. Differences in chromosomal structures may contribute to this wide variation in yield. A contig of about 800 kb, consisting of 19 clones, was constructed in the Pi-ta2 region. This region had a high frequency of repetitive sequences. To circumvent this difficulty, we devised a "two-step walking" method. The contig spanned a 300 kb region between markers located at 0 cM and 0.3 cM from Pi-ta. The ratio of physical to genetic distances (> 1,000 kb/cM) was more than three times larger than the average of rice (300 kb/cM). The low recombination rate and high frequency of repetitive sequences may also be related to the near centromeric character of this region. Fluorescent in situ hybridization (FISH) with a BAC clone from the Pi-b region yielded very clear signals on the long arm of chromosome 2, while a clone from the Pi-ta2 region showed various cross-hybridizing signals near the centromeric regions of all chromosomes.

Centromere↗
PubMed2003

High resolution genetic mapping and candidate gene identification at the xa5 locus for bacterial blight resistance in rice ( Oryza sativa L.).

The xa5 resistance gene from rice provides recessive, race-specific resistance to bacterial blight of rice caused by the pathogen Xanthomonas oryzae pv oryzae. A high-resolution genetic map of the chromosomal region surrounding xa5 was developed by placing 44 DNA markers on the distal end of rice chromosome 5. The basis for mapping was a PCR-based screening of 1,016 F(2) individuals derived from a cross between a near-isogenic line (NIL) and its corresponding recurrent parent to identify recombinants in the region. Recombinant F(2) individuals were progeny tested using F(3) families inoculated with the Philippine strain PXO 61 of bacterial blight pathogen. The xa5 gene was mapped to a 0.5-cM interval between the markers RS7 and RM611, which spanned an interval of approximately 70 kb and contained a total of 11 open reading frames. Sequence data for the locus was generated from an Indica (the IR24 isoline, IRBB21) BAC covering part of the region and compared to other overlapping Indica (cv 93-11) and Japonica (cv Nipponbare) sequences. Candidate-gene analysis revealed that a basal transcription factor (TFIIa), an ABC transporter, a tRNA synthase, a MAP kinase and a cysteine protease, as well as four unknown, hypothetical or putative proteins, are encoded at the locus and could be potential candidates for the resistance gene product. The mechanism by which these genes could provide recessive, race-specific resistance will be elucidated by map-based cloning of the xa5 gene.

Chromosomes, Artificial, Bacterial↗
PubMed2004

Genome-wide analysis of defense-responsive genes in bacterial blight resistance of rice mediated by the recessive R gene xa13.

Defense responses triggered by dominant and recessive disease resistance (R) genes are presumed to be regulated by different molecular mechanisms. In order to characterize the genes activated in defense responses against bacterial blight mediated by the recessive R gene xa13, two pathogen-induced subtraction cDNA libraries were constructed using the resistant rice line IRBB13--which carries xa13--and its susceptible, near-isogenic, parental line IR24. Clustering analysis of expressed sequence tags (ESTs) identified 702 unique expressed sequences as being involved in the defense responses triggered by xa13; 16% of these are new rice ESTs. These sequences define 702 genes, putatively encoding a wide range of products, including defense-responsive genes commonly involved in different host-pathogen interactions, genes that have not previously been reported to be associated with pathogen-induced defense responses, and genes (38%) with no homology to previously described functional genes. In addition, R-like genes putatively encoding nucleotide-binding site/leucine rich repeat (NBS-LRR) and LRR receptor kinase proteins were observed to be induced in the disease resistance activated by xa13. A total of 568 defense-responsive ESTs were mapped to 588 loci on the rice molecular linkage map through bioinformatic analysis. About 48% of the mapped ESTs co-localized with quantitative trait loci (QTLs) for resistance to various rice diseases, including bacterial blight, rice blast, sheath blight and yellow mottle virus. Furthermore, some defense-responsive sequences were conserved at similar locations on different chromosomes. These results reveal the complexity of xa13-mediated resistance. The information obtained in this study provides a large source of candidate genes for understanding the molecular bases of defense responses activated by recessive R genes and of quantitative disease resistance.

Chromosomes, Plant↗
PubMed1997

The molecular basis of disease resistance in rice.

The rice gene Xa21 conferring resistance to Xanthomonas oryzae pv. oryzae (Xoo), was isolated using a map-based cloning strategy. Compared with previously cloned genes, the structure of Xa21 represents a novel class of plant disease R genes encoding a putative receptor kinase (RK). This article proposes a model for the mode of action of Xa21 and summarizes our current knowledge of the modular basis of resistance in rice to bacterial leaf blight and blast.

Genes, Plant↗
PubMed2003

Genetic and physical mapping of a new gene for bacterial blight resistance in rice.

The inheritance of resistance for bacterial blight, caused by Xanthomonas oryzae pv. oryzae ( Xoo), was studied in Minghui 63, an elite restorer line for a number of widely used rice hybrids in China. A new dominant gene against a Chinese Xoo strain JL691 in both the seedling and adult stages was identified in Minghui 63 and designated as Xa26( t). Using a total of 477 highly susceptible individuals from an F(2) population, the Xa26( t) locus was mapped to a region of about 1.68 cM. This locus co-segregated with marker R1506 and was 0.21 cM from marker RM224 on one side and 1.47 cM from marker Y6855RA on the other side, in rice chromosome 11. A contig map, composed of five non-redundant bacterial artificial chromosome (BAC) clones and spanning approximately 500 kb in length, was constructed. Analysis of recombination events in the Xa26( t) region with the highly susceptible F(2) individuals anchored the gene locus to a region covered by three overlapped BAC clones. Assay of the lines showing a double crossover in marker loci flanking Xa26( t), in a population of recombinant inbred lines carrying Xa26( t), further delineated the gene to a 20-kb fragment. The Xa26( t) locus is tightly linked to another bacterial blight resistance gene locus, Xa4.

Chromosomes, Artificial, Bacterial↗
PubMed2000

Constitutive expression of the defense-related Rir1b gene in transgenic rice plants confers enhanced resistance to the rice blast fungus Magnaporthe grisea.

The Rirlb gene of rice (Oryza sativa) is one of a set of putative defense genes whose transcripts accumulate upon inoculation of rice with the non-host pathogen Pseudomonas syringae pv. syringae. It belongs to a family of genes encoding small extracellular proteins so far only identified in cereals. To assess the function of the Rirlb gene in rice blast resistance, it was placed under the control of the CaMV 35S promoter and transferred into rice plants of the japonica variety Taipei 309 by biolistic transformation of immature embryos. Two out of 12 hygromycin-resistant regenerated plants (OE1 and OE3) were fertile. DNA gel blot analysis suggested that these two T0 plants were independent transformants, each of which had stably incorporated one complete copy of the transgene into the genome. In addition, the OE1 plant appeared also a contain a rearranged copy or incomplete copy. T1 plants homozygous for the transgene were identified by DNA gel blot analysis of individual T2 progeny and further propagated. Expression analysis of the transgene showed that the transgene was active both in T1 plants and homozygous decendants. Challenge inoculation of homozygous transgenic plants with Magnaporthe grisea, the causal agent of rice blast disease, revealed that both independent transgenic lines were more resistant than the untransformed wild type, suggesting that over-expression of the Rirlb gene confers partial resistance against this important pathogen.

Gene Expression Regulation, Plant↗
PubMed2002

Identification of a 47-kb DNA fragment containing Xa4, a locus for bacterial blight resistance in rice.

Bacterial blight caused by Xanthomonas oryzae pv oryzae is a devastating disease in rice worldwide. The resistance gene Xa4 has been widely used in breeding programs and played an important role in protecting rice from this disease. Using 642 highly susceptible individuals and a random sample of 255 individuals from an F(2) population developed from a cross between IRBB4 and IR24, the Xa4 gene was genetically mapped to a region less than 1 cM. A contig map was constructed for the Xa4 region consisting of six non-redundant bacterial artificial chromosome (BAC) clones and spanning approximately 500 kb in length. Analysis of recombination events in the Xa4 region located the gene locus to one BAC, 3H8. Assay of the recombinants using the subclones of 3H8 in combination with sequence analysis further narrowed the Xa4 locus down to a 47-kb fragment.

Chromosome Mapping↗
PubMed2005

Targeting xa13, a recessive gene for bacterial blight resistance in rice.

Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most serious diseases of rice worldwide. Thirty bacterial blight resistance (R) genes (21 dominant genes and 9 recessive genes) in rice have been identified. They are the main sources for the genetic improvement of rice for resistance to Xoo. However, little is known about the recessive R genes. To clone and characterize the recessive R genes, we fine-mapped xa13, a fully recessive gene for Xoo resistance, to a DNA fragment of 14.8 kb using the map-based cloning strategy and a series of sequence-based molecular markers. Sequence analysis of this fragment indicated that this region contains only two apparently intact candidate genes (an extensin-like gene and a homologue of nodulin MtN3) and the 5' end of a predicted hypothetical gene. These results will greatly facilitate the isolation and characterization of xa13. Four PCR-based markers, E6a, SR6, ST9 and SR11 that were tightly linked to the xa13 locus, were also developed. These markers will be useful tools for the marker-assisted selection of xa13 in breeding programs.

Chromosomes, Plant↗
PubMed2002

Chloroisonicotinamide derivative induces a broad range of disease resistance in rice and tobacco.

Systemic acquired resistance (SAR) is a potent innate immunity system in plants that is effective against a broad range of pathogens. SAR in dicotyledonous plants such as tobacco and Arabidopsis has been partially elucidated and is mediated by salicylic acid (SA). However, the SAR mechanism of monocotyledonous rice plants remains to be clarified, although some similarities between SAR mechanisms in both types have been reported. Here we have characterized N-cyanomethyl-2-chloroisonicotinamide (NCI) as an effective SAR inducer in both plant species. Soil drench application of NCI induces a broad range of disease resistance in tobacco and rice and, more specifically, PR gene expression in tobacco. Both SA measurements in wild-type NCI-treated tobacco and pathogenic infection studies using NahG transgenic tobacco plants indicate that NCI-induced resistance enhancement does not require SA. Therefore, it is suggested that NCI induces SAR by triggering signaling at the same level as or downstream of SA accumulation as do both benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester and 2,6-dichloroisonicotinic acid. The fact that all of these chemicals are effective in rice and tobacco suggests that several common components function in disease resistance in both plant species.

Bacteria↗