Rye B chromosomes, which are supernumerary chromosomes dispensable for the host but increase in number by non-disjunction after meiosis, have been reported to affect meiotic homoeologous pairing in wheat-rye hybrids. The effect of a rye B chromosome (B) and its segments (B-9 and B-10) on homoeologous pairing was studied in hybrids between common wheat (2n = 42) and Aegilops variabilis (2n = 28), with reference to the Ph1 gene located on wheat chromosome 5B. The B-9 and B-10 chromosomes are derived from reciprocal translocations between a wheat and the B chromosomes, and the former had the B pericentromeric segment and the latter had the B distal segment. Both the B and B-9 chromosomes suppressed homoeologous pairing when chromosome 5B was absent. On the other hand, the B-9 and B-10 chromosomes promoted homoeologous pairing when 5B was present. On pairing suppression, B-9 had a greater effect in one dose than in two doses, and B-9 had a greater effect than B-10 had in one dose. These results suggested that the effect of the B chromosomes on homoeologous pairing was not confined to a specific region and that the intensity of the effect varied depending on the presence or absence of 5B and also on the segment and dose of the B chromosome. The mean chiasma frequency (10.23) in a hybrid (2n = 36) possessing 5B and one B-9 was considerably higher than that (2.78) of a hybrid (2n = 35) possessing 5B alone, and was comparable with that (14.09) of a hybrid (2n = 34) lacking 5B. This fact suggested that the B chromosome or its segment can be used in introducing alien genes into wheat by inducing homoeologous pairing between wheat and alien chromosome.

View full abstract

Common wheat (Triticum aestivum L.) is an allohexaploid that originated from natural hybridization between tetraploid wheat (Triticum turgidum) and diploid Aegilops tauschii. Ae. tauschii is considered one of the potential sources of new genetic variation in abiotic stress tolerance for improving common wheat. Abscisic acid (ABA) plays an important role in plant adaptation to environmental stresses. In this study, ABA responsiveness of 67 Ae. tauschii accessions and their synthetic hexaploid wheat lines, derived from crosses between T. turgidum cv. Langdon and the Ae. tauschii accessions, was evaluated based on growth inhibition by 20 μM ABA. Wide variation was found in ABA responsiveness for both synthetic wheat lines and their parental Ae. tauschii accessions. The variations due to D-genome found at the diploid level were also expressed in a hexaploid genetic background. Two pairs of synthetic wheat lines differing in ABA responsiveness were then selected for gene expression analysis and to test abiotic stress tolerance, because their parental Ae. tauschii accessions similarly exhibited the differential response to ABA. Gene expression of ABA inducible transcription factor, WABI5, and the downstream Cor/Lea genes (Wrab17, Wdhn13 and Wrab18) were analysed. In one pair, the highly responsive line exhibited higher induction of Wrab17 by ABA treatment, but no significant difference in dehydration or salinity tolerance was observed between these lines. In contrast, in the second pair, the highly ABA-responsive line showed higher levels of Wdhn13 expression and dehydration and salinity tolerance. In synthetic wheat lines, the difference in the ABA responsiveness of the lines appeared to be determined by the different sets of D-genome genes. Our findings suggest that highly ABA-responsive Ae. tauschii accessions should be valuable genetic resources for improving the abiotic stress tolerance of common wheat.

View full abstract

Some varieties of Brassica napus (rapeseed) and B. rapa contain a liner mitochondrial plasmid that is unique in that it can be inherited from the male parent through the pollen. We found that two rapeseed cultivars, Norin 16 and Westar, showed different rates of plasmid inheritance from the paternal parent (78.8% and 27.5%, respectively). To identify nuclear genes controlling the inheritance of the plasmid, we carried out quantitative trait locus (QTL) analyses using F₂ populations derived from a cross between these two cultivars. The F₁ plants transmitted the plasmid from the paternal plant at a frequency of approximately 60%; the transmission rates of the F₂ lines varied greatly, from 0 to 100%, with an average of 68.2%. A genetic map was constructed based on the segregation of 175 loci in the 102 F₂ plants. A total of 22 linkage groups were obtained, all of which could be assigned to the 19 rapeseed chromosomes. The total map length was 1374.7 cM, with an average distance of 7.9 cM between the markers. We found that three quantitative trait loci for plasmid paternal transfer, qPpt1, qPpt2 and qPpt3, located on chromosomes A5, C2 and C9, respectively, were significantly linked to the transmission frequency, whose the logarithm of odds (LOD) score were 4.97, 3.49 and 3.57, respectively. Their explained phenotypic variances were 25.0%, 22.2% and 37.1%, respectively. These results suggest that the paternal inheritance of the mitochondrial plasmid is controlled by a relatively small number of nuclear genes.

View full abstract

We examined pelage color variation in wild populations of black rats (the Rattus rattus species complex) in the Yambaru forest area, northern Okinawa Island, Ryukyu Archipelago, Japan. Our field study revealed that 8.7% (38/438) and 0.2% (4/2500) of rats exhibited two types of coat color: white spotting and melanism, respectively. Using 34 representative animals, the phylogeography of the population was inferred using a nuclear gene marker, i.e., sequences (954 bp) of the melanocortin-1 receptor (Mc1r) gene responsible for the melanistic form in black rats. Four sequences from Okinawa were characterized as R. tanezumi, the Asian strain of black rat. Notably, neither of the phenotypic characters of white spotting or melanism was associated with the Mc1r haplotypes. Analysis of mitochondrial cytochrome b (Cytb) sequences (1140 bp) revealed that four haplotypes recovered from Okinawa clustered with the clade of R. tanezumi and differed by one or more bases from haplotypes at other localities in Japan and Asian countries. Thus, both variants may have arisen in the native rat population of Okinawa without interaction with the lineage of R. rattus, which exhibits a worldwide distribution and displays such coat color variants. The Yambaru population of black rats has thus experienced its own evolutionary history in allopatry for a substantial period of time (e.g., 10,000 years), which has preserved valuable genetic polymorphisms and will be useful for assessing the ecological consequences of genetic variation in natural populations.

View full abstract

Crocodile newts, which constitute the genera Echinotriton and Tylototriton, are known as living fossils, and these genera comprise many endangered species. To identify mitochondrial (mt) genes suitable for future population genetic analyses for endangered taxa, we determined the complete nucleotide sequences of the mt genomes of the Japanese crocodile newt Echinotriton andersoni and Himalayan crocodile newt Tylototriton verrucosus. Although the control region (CR) is known as the most variable mtDNA region in many animal taxa, the CRs of crocodile newts are highly conservative. Rather, the genes of NADH dehydrogenase subunits and ATPase subunit 6 were found to have high sequence divergences and to be usable for population genetics studies. To estimate the inter-population divergence ages of E. andersoni endemic to the Ryukyu Islands, we performed molecular dating analysis using whole and partial mt genomic data. The estimated divergence ages of the inter-island individuals are older than the paleogeographic segmentation ages of the islands, suggesting that the lineage splits of E. andersoni populations were not caused by vicariant events. Our phylogenetic analysis with partial mt sequence data also suggests the existence of at least two more undescribed species in the genus Tylototriton. We also found unusual repeat sequences containing the 3′ region of cytochrome apoenzyme b gene, whole tRNA-Thr gene, and a noncoding region (the T-P noncoding region characteristic in caudate mtDNAs) from T. verrucosus mtDNA. Similar repeat sequences were found in two other Tylototriton species. The Tylototriton taxa with the repeats become a monophyletic group, indicating a single origin of the repeat sequences. The intra-and inter-specific comparisons of the repeat sequences suggest the occurrences of homologous recombination-based concerted evolution among the repeat sequences.

View full abstract

Imprinted genes have important effects on the regulation of fetal growth, development, and postnatal behavior. However, the study of imprinted genes has been limited in mammalian species other than human and mouse. Therefore, the study of porcine imprinted genes is useful for defining the extent of conservation of genomic imprinting among different species. In this study, the imprinting status of porcine NDN, MAGEL2 and MEST genes was determined by direct sequencing of the cDNAs and detection of single nucleotide polymorphisms (SNPs) identified in individuals from reciprocal crosses between Meishan and Large White pigs for allele discrimination. The analysis was carried out in 13 different tissues (skeletal muscle, fat, pituitary gland, heart, lung, liver, kidney, spleen, stomach, small intestine, uterus, ovary and testis) from 12 two-month-old piglets. Imprinting analysis showed that NDN and MAGEL2 were paternally expressed in all tissues where the genes were expressed as in human and mouse. Interestingly, MEST showed tissue-specific imprinting, being paternally expressed in skeletal muscle, fat, pituitary gland, heart, kidney, lung, stomach and uterus, and maternally expressed in spleen and liver.

View full abstract

HLA class II haplotypes often contain a second expressed HLA-DRB locus tightly linked to the classical HLA-DRB1 locus on the haplotype, which can be either HLA-DRB3, -DRB4 or -DRB5. These encode the HLA-DR51, -DR52 or -DR53 supertypic specificities and mark the ancestral lineages. HLA-DRB3/B4/B5 heterozygote excess in Welsh male newborns has been reported, suggesting a possibility of male-specific major histocompatibility complex (MHC)-mediated prenatal selection. However, it has not been confirmed in newborns of other ethnic groups or in adult populations. We analyzed the HLA-DRB1 and HLA-DRB3/B4/B5 genes in Korean newborns and healthy adults to examine whether MHC-mediated prenatal or postnatal selection exists. A total of 1,038 newborns (cord blood registry, 516 males and 522 females) and 2,082 healthy adults (hematopoietic stem cell donor registry, 1,111 males and 971 females) were HLA typed. HLA-DRB1/B3/B4/B5 DNA typing was performed using Dynal RELI^TM HLA-DRB SSO Kit (Dyanl Biotech, Wirral, U.K.). Genotype frequencies and homozygosity and heterozygosity rates for DRB3/B4/B5 supertypic loci were compared between males and females in newborns and adults. There were no significant differences in the HLA-DRB3/B4/B5 homozygosity and heterozygosity rates between males and females in both newborns and adults. In the comparison between newborns and adults, homozygosity rate was significantly higher in newborn females than in adult females (31.0% vs 25.0%, p = 0.01). Whether there is an age-related change from newborns toward adults has not been well studied in other populations, and further studies are warranted. In conclusion, male-specific heterozygosity excess reported in Welsh newborns has not been observed in Korean population, and there might be some ethnic differences in the gender-specific prenatal selection events.

View full abstract