A B-lectin receptor kinase gene conferring rice blast resistance

Rice blast, caused by the fungal pathogen Magnaporthe grisea, is one of the most devastating diseases in rice worldwide. The dominant resistance gene, Pi-d2 [previously named Pi-d(t)2], present in the rice variety Digu, confers gene-for-gene resistance to the Chinese blast strain, ZB15. Pi-d2 was previously mapped close to the centromere of chromosome 6. In this study, the Pi-d2 gene was isolated by a map-based cloning strategy. Pi-d2 encodes a receptor-like kinase protein with a predicted extracellular domain of a bulb-type mannose specific binding lectin (B-lectin) and an intracellular serine-threonine kinase domain. Pi-d2 is a single-copy gene that is constitutively expressed in the rice variety Digu. Transgenic plants carrying the Pi-d2 transgene confer race-specific resistance to the M. grisea strain, ZB15. The Pi-d2 protein is plasma membrane localized. A single amino acid difference at position 441 of Pi-d2 distinguishes resistant and susceptible alleles of rice blast resistance gene Pi-d2. Because of its novel extracellular domain, Pi-d2 represents a new class of plant resistance genes.  

The radish Rfo restorer gene of Ogura cytoplasmic male sterility encodes a protein with multiple pentatricopeptide repeats

A single radish nuclear gene, Rfo, restores Ogura (ogu) cytoplasmic male sterility (CMS) in Brassica napus. A map-based cloning approach relying on synteny between radish and Arabidopsis was used to clone Rfo. A radish gene encoding a 687-amino-acid protein with a predicted mitochondrial targeting pre-sequence was found to confer male fertility upon transformation into ogu CMS B. napus. This gene, like the recently described Petunia Rf gene, codes for a pentatricopeptide repeat (PPR)-containing protein with multiple, in this case 16, PPR domains. Two similar genes that do not appear to function as Rfo flank this gene. Comparison of the Rfo region with the syntenic Arabidopsis region indicates that a PPR gene is not present at the Rfo-equivalent site in Arabidopsis, although a smaller and related PPR gene is found about 40 kb from this site. The implications of these findings for the evolution of restorer genes and other PPR encoding genes are discussed.  

Construction and characterization of two rice bacterial artificial chromosome libraries from the parents of a permanent recombinant inbred mapping population

Rice is a leading grain crop and the staple food for over half of the world population. Rice is also an ideal species for genetic and biological studies of cereal crops and other monocotyledonous plants because of its small genome and well developed genetic system. To facilitate rice genome analysis leading to physical mapping, the identification of molecular markers closely linked to economic traits, and map-based cloning, we have constructed two rice bacterial artificial chromosome (BAC) libraries from the parents of a permanent mapping population (Lemont and Teqing) consisting of 400 F9 recombinant inbred lines (RILs). Lemont (japonica) and Teqing (indica) represent the two major genomes of cultivated rice, both are leading commercial varieties and widely used germplasm in rice breeding programs. The Lemont library contains 7296 clones with an average insert size of 150 kb, which represents 2.6 rice haploid genome equivalents. The Teqing library contains 14208 clones with an average insert size of 130 kb, which represents 4.4. rice haploid genome equivalents. Three single-copy DNA probes were used to screen the libraries and at least two overlapping BAC clones were isolated with each probe from each library, ranging from 45 to 260 kb in insert size. Hybridization of BAC clones with chloroplast DNA probes and fluorescent in situ hybridization using BAC DNA as probes demonstrated that both libraries contain very few clones of chloroplast DNA origin and are likely free of chimeric clones. These data indicate that both BAC libraries should be suitable for map-based cloning of rice genes and physical mapping of the rice genome.  

Map-based cloning of the ALK gene, which controls the gelatinization temperature of rice

As a primary crop in China, rice provides the staple food for more than 50% population in the world. With the increasing grain yield and improvement of living conditions, grain quality has drawn more and more attention. Gelatinization temperature (GT), an important parameter for rice cooking quality, is the critical temperature at which the starch granules start to lose crystallinity and birefringence by irreversible expanding and to change the starch surface from polarized to soluble state c…  

The broad-spectrum potato cyst nematode resistance gene (Hero) from tomato is the only member of a large gene family of NBS-LRR genes with an unusual amino acid repeat in the LRR region

The Hero gene of tomato is a broad spectrum resistance gene that confers a high level of resistance to all pathotypes of the potato cyst nematodes Globodera rostochiensis and partial resistance to G. pallida. The gene was identified by map-based cloning, sequencing and complementation analysis of two susceptible tomato lines with an array of 13 overlapping cosmids spanning a total distance of 135 kb. Hero encodes a protein with a nucleotide-binding site (NBS) and a leucine-rich-repeat (LRR) domain and is a member of a gene family of 14 highly homologous genes, which are clustered within a continuous 118-kb region. The isolated Hero gene displayed resistance to various G. rostochiensis pathotypes and partial resistance to G. pallida pathotype Pa2/3 in transgenic tomato lines. None of the Hero homologues conferred resistance to G. rostochiensis pathotypes. Hero can be distinguished from its homologues by the length of a compound hexanucleotide microsatellite, which codes for a charged and repetitive amino acid domain within the LRR. We propose that the expansion of this microsatellite may be involved in the evolution of the Hero resistance gene.  

Suppressed recombination around the MXC3 locus, a major gene for resistance to poplar leaf rust

A positional cloning strategy is being implemented in Populus for the isolation of the dominant MXC3 allele, which confers resistance to poplar leaf rust caused by Melampsora×columbiana (pathotype 3). AFLP markers were used to saturate the chromosomal region around the MXC3 locus in a large (n=1,902) Populus trichocarpa×P. deltoides (T×D) mapping pedigree segregating 1:1 for rust resistance and susceptibility. The high-resolution linkage map developed around the MXC3 locus contains 19 AFLP markers and spans a genetic distance of 2.73 cM. Of the 19 AFLP markers, seven were found to co-segregate with the locus. One co-segregating AFLP marker, CCG.GCT_01, was converted to an STS marker (BVS1) and used to identify a physical contig of overlapping BAC clones from the MXC3 region. Genetic and physical mapping of markers isolated from the BAC contig failed to delimit the MXC3 locus within a 300-kb interval defined by the overlapping BAC clones. This result indicates a >25-fold reduction in recombination frequency in the MXC3 region compared to the average rate of recombination for the Populus genome. Received: 8 December 2000 / Accepted: 1 March 2001  

植物基因的图位克隆

图位克隆是基因的有效方法，本文概述了植物基因图位克隆的研究进展，主要包括图位克隆的一般策略、相关技术、发展前景和其它基因组领域研究于其带来的有益借鉴。  

Rice Chlorina-1 and Chlorina-9 encode ChlD and ChlI subunits of Mg-chelatase, a key enzyme for chlorophyll synthesis and chloroplast development

Photosynthetic organisms exhibit a green color due to the accumulation of chlorophyll pigments in chloroplasts. Mg-protoporphyrin IX chelatase (Mg-chelatase) comprises three subunits (ChlH, ChlD and ChlI) and catalyzes the insertion of Mg²⁺ into protoporphyrin IX, the last common intermediate precursor in both chlorophyll and heme biosyntheses, to produce Mg-protoporphyrin IX (MgProto). Chlorophyll deficiency in higher plants results in chlorina (yellowish-green) phenotype. To date, 10 chlorina (chl) mutants have been isolated in rice, but the corresponding genes have not yet been identified. Rice Chl1 and Chl9 genes were mapped to chromosome 3 and isolated by map-based cloning. A missense mutation occurred in a highly conserved amino acid of ChlD in the chl1 mutant and ChlI in the chl9 mutant. Ultrastructural analyses have revealed that the grana are poorly stacked, resulting in the underdevelopment of chloroplasts. In the seedlings fed with aminolevulinate-dipyridyl in darkness, MgProto levels in the chl1 and chl9 mutants decreased up to 25% and 31% of that in wild-type, respectively, indicating that the Mg-chelatase activity is significantly reduced, causing the eventual decrease in chlorophyll synthesis. Furthermore, Northern blot analysis indicated that the nuclear genes encoding the three subunits of Mg-chelatase and LhcpII in chl1 mutant are expressed about 2-fold higher than those in WT, but are not altered in the chl9 mutant. This result indicates that the ChlD subunit participates in negative feedback regulation of plastid-to-nucleus in the expression of nuclear genes encoding chloroplast proteins, but not the ChlI subunit.Haitao Zhang and Jinjie Li contributed equally to this work  

作物数量性状基因图位克隆研究进展

对数量性状基因(QTL)的鉴定和克隆不仅有利于从分子水平上阐明作物重要农艺性状的形成机理,而且对于有效开展这些性状的分子育种,进一步提高作物增产潜力具有重要意义.近年来作物QTL图位克隆取得了重要突破,一批QTL被成功克隆,而模式植物基因组研究的快速发展则为作物QTL图位克隆技术带来了新的策略和方法.本文就相关研究的主要进展和发展趋势进行了综述.  

The eukaryotic translation initiation factor 4E confers multiallelic recessive Bymovirus resistance in Hordeum vulgare (L.)

Virus diseases are widespread threats for crop production, which can, in many cases, be controlled efficiently by exploiting naturally occurring resistance. Barley, an important cereal species of the Triticeae, carries two genes, rym4 and rym5 , which are located in the telomeric region of chromosome 3HL and confer recessive resistance to various strains of the Barley yellow mosaic virus complex. The barley 'eukaryotic translation initiation factor 4E' ( Hv-eIF4E ) was identified as a candidate for resistance gene function by physical mapping on a 650 kb contig. It is located in a chromosomal region characterized by suppressed recombination, in a position collinear to its homologue on rice chromosome 1L. Sequence diversity in the coding region of Hv-eIF4E , as calculated from a collection of unrelated barley accessions, revealed non-silent single nucleotide polymorphisms (SNPs) in four of its five exons. Stable transformation of a resistant barley genotype with a genomic fragment or a full-length cDNA of Hv-eIF4E derived from susceptible cultivars induced susceptibility to Barley mild mosaic virus . Moreover, the identification of SNPs diagnostic for rym4 and rym5 provides evidence that these are two alleles, which confer different resistance specificities. These findings demonstrate that variants of Hv-eIF4E confer multiallelic recessive virus resistance in a monocot species. The identification of eIF4E as the causal host factor for bymovirus resistance illustrates that mutations in this basic component of the eukaryotic translation complex form a seminal mechanism for recessive virus resistance in both dicot and monocot plants.