Satoru Taura

Frequency and distribution in East Asia of 12 mutations identified in the SLC25A13 gene of Japanese patients with citrin deficiency

AbstractDeficiency of citrin, a liver-type mitochondrial aspartate-glutamate carrier (AGC), encoded by the SLC25A13 gene on chromosome 7q21.3, causes autosomal recessive disorders: adult-onset type II citrullinemia (CTLN2) and neonatal hepatitis associated with intrahepatic cholestasis (NICCD). So far, we have described 12 SLC25A13 mutations: 11 were from Japan and one from Israel. Three mutations found in Chinese and Vietnamese patients were the same as those in Japanese patients. In the present study, we identified a novel mutation IVS6+1G>C in a Japanese CTLN2 patient and widely screened 12 SLC25A13 mutations found in Japanese patients in control individuals from East Asia to confirm our preliminary results that the carrier frequency was high in Asian populations. Mutations 851-854del and 1638-1660dup were found in all Asian countries tested, and 851-854del associated with 290-haplotype in microsatellite marker D7S1812 was especially frequent. Other mutations frequently detected were IVS11+1G>A in Japanese and Korean, S225X in Japanese, and IVS6+5G>A in Chinese populations. We found a remarkable difference in carrier rates in China (including Taiwan) between north (1/940) and south (1/48) of the Yangtze River. We detected many carriers in Chinese (64/4169 = 1/65), Japanese (20/1372 = 1/69) and Korean (22/2455 = 1/112) populations, suggesting that over 80,000 East Asians are homozygotes with two mutated SLC25A13 alleles.

Chromosomal Location of HWA1 and HWA2, Complementary Hybrid Weakness Genes in Rice

Hybrid weakness phenomena in rice reportedly have two causes: those of HWC1 and HWC2 genes and those of HWA1 and HWA2 genes. No detailed study of the latter has been reported. For this study, we first produced crosses among cultivars carrying the weakness-causing allele on the HWA1 and HWA2 loci to confirm the phenotype of the hybrid weakness and the genotypes of the cultivars on the two loci, as reported earlier. We then confirmed that these cultivars belong to Indica. Subsequent linkage analysis of HWA1 and HWA2 genes conducted using DNA markers revealed that both genes are located in the 1,637-kb region, surrounded by the same DNA markers on the long arm of chromosome 11. The possibility of allelic interaction inducing hybrid weakness is discussed.

Identification and linkage analysis of a new rice bacterial blight resistance gene from XM14, a mutant line from IR24

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a chief factor limiting rice productivity worldwide. XM14, a rice mutant line resistant to Xoo, has been obtained by treating IR24, which is susceptible to six Philippine Xoo races and six Japanese Xoo races, with N-methyl-N-nitrosourea. XM14 showed resistance to six Japanese Xoo races. The F2 population from XM14 × IR24 clearly showed 1 resistant : 3 susceptible segregation, suggesting control of resistance by a recessive gene. The approximate chromosomal location of the resistance gene was determined using 10 plants with shortest lesion length in the F2 population from XM14 × Koshihikari, which is susceptible to Japanese Xoo races. DNA marker-assisted analysis revealed that the gene was located on chromosome 3. IAS16 line carries IR24 genetic background with a Japonica cultivar Asominori segment of chromosome 3, on which the resistance gene locus was thought to be located. The F2 population from IAS16 × XM14 showed a discrete distribution. Linkage analysis indicated that the gene is located around the centromeric region. The resistance gene in XM14 was a new gene, named XA42. This gene is expected to be useful for resistance breeding programs and for genetic analysis of Xoo resistance.

Chromosomal Location of HCA1 and HCA2, Hybrid Chlorosis Genes in Rice

Many postzygotic reproductive barrier forms have been reported in plants: hybrid weakness, hybrid necrosis, and hybrid chlorosis. In this study, linkage analysis of the genes causing hybrid chlorosis in F2 generation in rice, HCA1 and HCA2, was performed. HCA1 and HCA2 are located respectively on the distal regions of the short arms of chromosomes 12 and 11. These regions are known to be highly conserved as a duplicated chromosomal segment. The molecular mechanism causing F2 chlorosis deduced from the location of the two genes was discussed. The possibility of the introgression of the chromosomal segments encompassing HCA1 and/or HCA2 was also discussed from the viewpoint of Indica-Japonica differentiation.

Cloning, expression, and efficient purification in Escherichia coli of a halophilic nucleoside diphosphate kinase from the moderate halophile Halomonas sp. #593

Most typical halophilic enzymes from extremely halophilic archaea require high concentrations of salt for their activity and stability. These enzymes are inactive in Escherichia coli unless refolded in the presence of salts in vitro. In this report, we describe cloning of the ndk gene of nucleoside diphosphate kinase from a moderately halophilic eubacterium and overexpression of the protein in E. coli as an N-terminal hexa-His fusion to facilitate its purification on Ni-NTA affinity resin. We demonstrate evidence that the protein is properly folded and exhibits the same specific activity and stability as the native protein from Halomonas cells.

Secretion of Escherichia coli DsbA and DsbC proteins from Brevibacillus choshinensis: stimulation of human epidermal growth factor production

DsbA and DsbC, members of the thioredoxin super-family of redox proteins, which are expressed in the periplasmic space of Escherichia coli, were cloned into and successfully secreted from Brevibacillus choshinensis at ∼100 μg ml−1. Both proteins were active in exchanging disulfide bonds of bovine insulin in vitro. Furthermore, DsbA secreted by B. choshinensis promoted the conversion of non-native human epidermal growth factor to the native form.

Genetic analysis of ion-beam induced extremely late heading mutants in rice.

Two extremely late heading mutants were induced by ion beam irradiation in rice cultivar ‘Taichung 65’: KGM26 and KGM27. The F2 populations from the cross between the two mutants and Taichung 65 showed clear 3 early: 1 late segregation, suggesting control of late heading by a recessive gene. The genes identified in KGM26 and KGM27 were respectively designated as FLT1 and FLT2. The two genes were mapped using the crosses between the two mutants and an Indica cultivar ‘Kasalath’. FLT1 was located on the distal end of the short arm of chromosome 8. FLT2 was located around the centromere of chromosome 9. FLT1 might share the same locus as EHD3 because their chromosomal location is overlapping. FLT2 is inferred to be a new gene because no gene with a comparable effect to that of this gene was mapped near the centromere of chromosome 9. In crosses with Kasalath, homozygotes of late heading mutant genes showed a large variation of days to heading, suggesting that other genes affected late heading mutant genes.

High-resolution mapping and characterization of xa42, a resistance gene against multiple Xanthomonas oryzae pv. oryzae races in rice (Oryza sativa L.)

Improvement of resistance against rice bacterial blight (BB) disease is an important breeding strategy in breeding programs across the world, especially in Africa and southern Asia where BB is more prevalent. This report describes a high-resolution map and characterization of xa42 at XA42 locus, a rice BB resistance gene in XM14, a mutant line originating from IR24. The candidate gene region was narrowed down from 582 kb, which had been obtained in our previous study, to 57 kb. XM14 shows brown spots in its leaves like lesion mimic mutants. This line also shows a shorter stature than the original cultivar IR24. In XA42 gene segregating populations, homozygotes of xa42 allele were consistently resistant to the six Japanese Xanthomonas oryzae pv. oryzae races used for this study. They also showed brown spots and markedly short stature compared with the other genotypes, suggesting that xa42 gene exhibits pleiotropic effects.

Distribution of Hwc2-1, a causal gene of a hybrid weakness, in the World Rice Core collection and the Japanese Rice mini Core collection: its implications for varietal differentiation and artificial selection

A pair of complementary genes, Hwc1-1 at HWC1 locus and Hwc2-1 at HWC2 locus, cause a weakness phenomenon in rice. For this study, we performed haplotype analysis around the HWC2 locus in two core collections comprising 119 accessions. We also examined reactions to phenol and Xanthomonas oryzae pv. oryzae (Xoo) Japanese race I. To elucidate the genetic relations among all accessions, we analyzed their banding patterns of 40 Indel markers covering the rice genome. The classification by Indel markers was almost consistent with that using 4,357 SNPs. The testcross with Hwc1-1 carrier indicated that 37 accessions carried Hwc2-1 allele, whereas 82 carried hwc2-2 allele. Strong association between HWC2 and Ph genes was observed. Based on 14 DNA markers around HWC2 locus and Ph genotype, the 119 accessions were divided into 50 haplotypes. To examine the HWC2 candidate chromosomal region specifically, the ‘haplotype group’ characterized by the six DNA markers closely linked with HWC2 were analyzed. Hwc2-1 carriers had the same haplotype group. Some hwc2-2 haplotype groups were associated with resistance against the Xoo race. The relation between varietal differentiation and haplotypes around the HWC2 locus was discussed, along with its breeding significance.