Blast Resistance Genes Pi-b Research Articles

Development of rice variety with blast resistance genes Pi-b and Pi-z basing on DNA-technologies

The article presents stages of development and testing new rice variety Nautilus with blast resistance genes Pi-b and Pi-z. Basing on the use of DNA-marking methods, breeding material carrying the target genes was developed. The obtained material was studied in the links of breeding process in the field. Based on the results of field testing, 6 lines were identified, of which VNIIR 6016 turned out to be the best in terms of a complex of economically valuable traits. In 2016, this sample was transferred to the State variety testing under the name Nautilus. In 2019, a new rice variety Nautilus was included in the register of breeding achievements and approved for use in the Russian Federation in Krasnodar region. The study of variety Nautilus in 2019-2020 in an ecological test confirmed its high resistance to blast, in comparison with other released varieties. It took 10 - 12 years to develop the variety.

Geographically Distinct and Domain-Specific Sequence Variations in the Alleles of Rice Blast Resistance Gene Pib.

Rice blast is caused by Magnaporthe oryzae, which is the most destructive fungal pathogen affecting rice growing regions worldwide. The rice blast resistance gene Pib confers broad-spectrum resistance against Southeast Asian M. oryzae races. We investigated the allelic diversity of Pib in rice germplasm originating from 12 major rice growing countries. Twenty-five new Pib alleles were identified that have unique single nucleotide polymorphisms (SNPs), insertions and/or deletions, in addition to the polymorphic nucleotides that are shared between the different alleles. These partially or completely shared polymorphic nucleotides indicate frequent sequence exchange events between the Pib alleles. In some of the new Pib alleles, nucleotide diversity is high in the LRR domain, whereas, in others it is distributed among the NB-ARC and LRR domains. Most of the polymorphic amino acids in LRR and NB-ARC2 domains are predicted as solvent-exposed. Several of the alleles and the unique SNPs are country specific, suggesting a diversifying selection of alleles in various geographical locations in response to the locally prevalent M. oryzae population. Together, the new Pib alleles are an important genetic resource for rice blast resistance breeding programs and provide new information on rice-M. oryzae interactions at the molecular level.

Identification of genetic markers linked to anthracnose resistance in sorghum using association analysis

Anthracnose in sorghum caused by Colletotrichum sublineolum is one of the most destructive diseases affecting sorghum production under warm and humid conditions. Markers and genes linked to resistance to the disease are important for plant breeding. Using 14,739 SNP markers, we have mapped eight loci linked to resistance in sorghum through association analysis of a sorghum mini-core collection consisting of 242 diverse accessions evaluated for anthracnose resistance for 2 years in the field. The mini-core was representative of the International Crops Research Institute for the Semi-Arid Tropics' world-wide sorghum landrace collection. Eight marker loci were associated with anthracnose resistance in both years. Except locus 8, disease resistance-related genes were found in all loci based on their physical distance from linked SNP markers. These include two NB-ARC class of R genes on chromosome 10 that were partially homologous to the rice blast resistance gene Pib, two hypersensitive response-related genes: autophagy-related protein 3 on chromosome 1 and 4 harpin-induced 1 (Hin1) homologs on chromosome 8, a RAV transcription factor that is also part of R gene pathway, an oxysterol-binding protein that functions in the non-specific host resistance, and homologs of menthone:neomenthol reductase (MNR) that catalyzes a menthone reduction to produce the antimicrobial neomenthol. These genes and markers may be developed into molecular tools for genetic improvement of anthracnose resistance in sorghum.

Molecular Characterization of a Genomic Fragment ContainingPi-khGene from the Genomic Library ofIndicaRice Line Tetep

Identification of full length genes along with upstream regulatory elements is important to understand its expression. Here, we report preparation of high titre genomic library and identification of a genomic clone containing Pi-k h gene with its complete upstream and downstream sequences from the rice blast resistant line Tetep. Structural analysis of protein revealed that Pi-k h has a central nucleotide binding site domain, leucine-rich repeats domain and a unique zinc-finger domain. Comparative analysis of Pi-k h protein sequence showed 64% and 45% similarity with the protein sequences of rice blast resistance genes Pi-b and Pi-ta, respectively.

Search for donors of a race-specific rice blast resistance gene Pi-b by means of molecular marking methods

An intragenic codominant marker system for identifying gene Pi-b is used for searching for its donors in the working collection of initial breeding material of the All-Russian Rice Research Institute.

Inheritance of resistance to rice stripe virus in rice line `BL 1'

Rice stripe is the most serious virus disease in temperate rice-growing countries. The most economical and environmentally safe practice for controlling this disease is virus-resistant cultivars. ‘BL 1’ is an elite germplasm line with the blast resistance gene Pib, and has been used as a differential line for testing the pathogenicity of the blast fungus. We found that certain progenies from BL 1 showed resistance to both blast and rice stripe virus (RSV). The objectives of this study were to evaluate the RSV resistance in the field and under artificial conditions, to assess the reaction to the insect vector(small brown plant hopper, SBPH), and to examine its inheritance and its relationship to blast resistance in BL 1.BL 1 was susceptible to SBPH, but resistant to RSV in field and artificial inoculation tests. The inheritance of RSV resistance in F3 lines from the cross Nipponbare (NPB)/BL 1 was studied using artificial inoculation with a population of viruliferous SBPH. A serological assay for RSV infection using an enzyme-linked immunosorbent assay (ELISA) was used. RSV resistance in BL 1 was controlled by a single major gene with incomplete dominance. The locus responsible for RSV resistance was genetically independent of the blast resistance gene Pib. The resistance gene for RSV infection in BL 1 was also independent of Stvb-i, a gene widely distributed in resistant Japanese cultivars. Resistance to RSV must be diversified in rice cultivars considering the potential for future emergence of new RSV strains. The new resistance gene identified in BL 1, which has improved plant type and blast resistance, is considered useful for breeding RSV-resistant cultivars in japonica rice.

Expression of the Pib rice-blast-resistance gene family is up-regulated by environmental conditions favouring infection and by chemical signals that trigger secondary plant defences.

The rice blast resistance gene Pib is a member of the nucleotide binding site (NBS) and leucine-rich repeat (LRR) class of plant disease resistance (R) genes and belongs to a small gene family. We describe here the isolation and characterization of a Pib homologue (PibH8), and extensive investigation of the expression of the Pib gene family (Pib, PibH8, HPibH8-1, HPibH8-2) under various environmental and chemical treatments. PibH8 shows 42% identity and 60% similarity to Pib and, like Pib, has a duplication of the kinase 1a, 2, and 3a motifs of the NBS region in the N-terminal half of the protein. Interestingly, genes of the Pib family exhibit a diurnal rhythm of expression. RNA gel blot analysis revealed that their expression was regulated dramatically by environmental signals. such as temperature, light and water availability. Their expression was also induced by chemical treatments, such as jasmonic acid, salicylic acid, ethylene and probenazole. Our findings suggest that expression of the Pib gene family is up-regulated by environmental conditions that would favour pathogen infection. This may reflect the evolution of anticipatory control of R gene expression.

An approach to cloning of Pi-b rice blast resistance gene

A contig of clones from BAC rice genomic library encompassing blast resistance gene Pi-b was constructed. On an average eight clones (8 ± 2.6) were picked up by each marker, which was expected basing on the BAC library size (Nakamura et al. 1997). The 2.4 cM distance between flanking RFLP markers G 1234 and RZ 213 (Miyamoto et al. 1996) was spanned with 4 steps of contig including 25 clones. The physical distance of 370 kb between flanking markers corresponds to a small ratio of physical and genetical distances (155 kb/cM) due to a probable structure of the gene locus near the telomeric end of the chromosome. Markers cosegregating with blast resistance against Magnoporthe grisea were localized in a 2 kb restriction fragment. A new border marker was found on the telomeric side of the Pi-b gene, less than 10 kb from cosegregating markers. No clear marker for the centromeric side of the gene was found but the position of Pi-b rice blast resistant gene was narrowed to within at least 50 kb, which is to our knowledge the most precised estimation of the position of this gene.

Fine and physical mapping toward the positional cloning of an indica-derived blast resistance gene Pi-b

Fine and physical mapping toward the positional cloning of an indica-derived blast resistance gene Pi-b

High Resolution Mapping of the/ndica-Derived Rice Blast Resistance Genes. I.Pi-b

Rice is a good material for studying positional cloning of disease resistance genes because its ratio of physical to genetic distance is small (100 to 300 kb/cM), and abundant genetic information is available. As a first step in cloning, the rice blast resistance gene Pi-b was finely mapped near the terminal region of chromosome 2 using restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) markers. Various near-isogenic lines (NILs) developed by the introgression of the indica-derived Pi-b gene into japonica recurrent parents facilitated its rapid and accurate localization and also the F2 analyses. Although Pi-b was introgressed independently from four cultivars, all the donors showed the same RFLP profile for all the nearby probes used, whereas there was some polymorphism among japonica recurrent parents, suggesting a single origin of the resistance gene. Pi-b cosegregated with RAPD (b-1) and RFLP (RZ123) markers, and it was bracketed between flanking RFLP markers at 0.5 cM on the centromeric side, and 1.9 cM on the telomeric side. The centromeric and telomeric limits of the indica regions of NILs BL-1 and BL-7 were closer to Pi-b than the flanking nucleic markers on each side, respectively, providing better (< 0.5 and < 1.9 cM) delineating markers. A long-range Southern blot with rare-cutter restriction enzymes revealed an 85-kb common band between the two 0-cM markers. These markers provide an excellent environment for the positional cloning of Pi-b.