Extensive biochemical and structural analyses have been performed on the putative DNA repair proteins of hyperthermophilic archaea, in contrast to the few genetic analyses of the genes encoding these proteins. Accordingly, little is known about the repair pathways used by archaeal cells at high temperature. Here, we attempted to disrupt the genes encoding the potential repair proteins in the genome of the hyperthermophilic archaeon Thermococcus kodakaraensis. We succeeded in isolating null mutants of the hjc, hef, hjm, xpb, and xpd genes, but not the radA, rad50, mre11, herA, nurA, and xpg/fen1 genes. Phenotypic analyses of the gene-disrupted strains showed that the xpb and xpd null mutants are only slightly sensitive to ultraviolet (UV) irradiation, methyl methanesulfonate (MMS) and mitomycin C (MMC), as compared with the wild-type strain. The hjm null mutant showed sensitivity specifically to mitomycin C. On the other hand, the null mutants of the hjc gene lacked increasing sensitivity to any type of DNA damage. The Hef protein is particularly important for maintaining genome homeostasis, by functioning in the repair of a wide variety of DNA damage in T. kodakaraensis cells. Deletion of the entire hef gene or of the segments encoding either its nuclease or helicase domain produced similar phenotypes. The high sensitivity of the Δhef mutants to MMC suggests that Hef performs a critical function in the repair process of DNA interstrand cross-links. These damage-sensitivity profiles suggest that the archaeal DNA repair system has processes depending on repair-related proteins different from those of eukaryotic and bacterial DNA repair systems using homologous repair proteins analyzed here.

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After landing on the stigma, the pollen grain germinates and elongates a tube to deliver its generative nuclei to the egg cell of the ovule. The molecular mechanisms involved in the drastic morphological changes in the pollen grain during this fertilization process remain largely unknown. In this study, the expression of 732 randomly selected genes in petunia pollen and pollen tubes was analyzed by microarray and quantitative PCR analyses. We found no evidence for up-regulation of any of these genes in the pollen tube. Our findings provide support at the gene level for the longstanding hypothesis that pollen germination and tube growth are not dependent on new RNA synthesis and that the large number of RNAs required for germination and tube growth are stored in mature pollen grains.

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It is known that the common cultivated rice (Oryza sativa) was domesticated from Asian wild rice, O. rufipogon. Among the morphological differences between them, loss of seed shattering is one of the striking characters specific for the cultivated forms. In order to understand the genetic control on shattering habit, QTL analysis was carried out using BC₂F₁ backcross population between O. sativa cv. Nipponbare (a recurrent parent) and O. rufipogon acc. W630 (a donor parent). As a result, two strong QTLs were detected on chromosomes 1 and 4, and they were found to be identical to the two major seed-shattering loci, qSH1 and sh4, respectively. The allelic interaction at these loci was further examined using two sets of backcross populations having reciprocal genetic backgrounds, cultivated and wild. In the genetic background of cultivated rice, the wild qSH1 allele has stronger effect on seed shattering than that of sh4. In addition, the wild alleles at both qSH1 and sh4 loci showed semi-dominant effects. On the other hand, in the genetic background of wild rice, non-shattering effects of Nipponbare alleles at both loci were examined to inspect rice domestication from a viewpoint of seed shattering. It was serendipitous that the backcross plants individually having Nipponbare homozygous alleles at either shattering locus (qSH1 or sh4) shed all the seeds. This fact strongly indicates that the non-shattering behavior was not obtained by a single mutation in the genetic background of wild rice. Probably, some other minor genes are still associated with the formation or activation of abscission layer, which enhance the seed shattering.

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In the near future, global average temperature is expected to increase due to the accumulation of greenhouse gases, and increased temperatures will cause severe sterility in many crop species. In rice, since wild species show high genetic variation, they may have the potential to improve the flowering characters of cultivars. In this study, we investigated flowering characters under natural conditions by comparing an Asian wild rice accession of Oryza rufipogon W630 (originated from Myanmar) with a Japanese rice cultivar, O. sativa Japonica cv. Nipponbare. Further, QTL analysis for days to heading (DH) and spikelet opening time (SOT: the time of day when the spikelet opens) was carried out using BC₂F₈ backcross population derived from the cross between them. Regarding DH, four QTLs were detected, and two of them were found to have wild alleles with strong effects leading to longer days to heading during the Japanese summer. These wild alleles may be used to produce late-heading cultivars that do not flower during the high summer temperatures anticipated in the future. As for SOT, two parameters of SOTb (beginning time when the first spikelet opens) and SOTm (median time when 50% of the spikelets open) were recorded and the time differences from Nipponbare were investigated. Two QTLs on chromosomes 5 and 10 and two QTLs on chromosomes 4 and 5 were detected for SOTb and SOTm, respectively. The wild alleles were responsible for early spikelet opening time at all loci. If the wild alleles detected in this study have the same effects in the genetic background of other cultivars, they will be very useful in producing early-flowering rice cultivars that complete fertilization in the morning before the temperature rises.

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Psathyrostachys huashanica Keng (2n = 14; N^hN^h) is an endangered wheat-related species, with a distribution in the Huashan region of central China. It has many agronomically promising characters including resistance to disease and drought and winter hardiness. We produced hybrids between common wheat as the female parent and P. huashanica as the male parent. From the offspring, we selected chromosome addition lines of common wheat carrying each of all seven chromosomes of P. huashanica. Four chromosomes (B, D, E and F) were recovered in disomic lines and three (A, C and G) in monosomic addition lines. These alien chromosomes were distinguished from each other by cytological analyses. Chromosome A was characterized by a 45S rDNA site in the subtelomeric region of the short arm. Chromosome B carried one 5S and one 45S rDNA sites co-localized in an interstitial region of the short arm, and the expression of the alien high-molecular-weight glutenin was observed in the endosperm of line B. Chromosome D had a 45S rDNA signal in the interstitial region of the long arm. Chromosomes C, E, and F were distinguished by the EST-SSR markers Ltc0464, Ltc0096, and Xcfe175, respectively. The homoeologous group of each alien chromosome was implied from the results above, and the utilization of these addition lines for wheat breeding was discussed.

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The oxidized nucleotide precursors 7, 8-dihydro-8-oxo-dGTP (8-oxo-dGTP) and 1, 2-dihydro-2-oxo-dATP (2-oxo-dATP) are readily incorporated into nascent DNA strands during replication, which would cause base substitution mutations. E. coli MutT and human homologue hMTH1 hydrolyze 8-oxo-dGTP, thereby preventing mutations. In this study, we searched for hMTH1 homologues in the ascidian Ciona intestinalis using the NCBI-BLAST database. Among several candidates, we focused on one open reading frame, designated as CiMutT, because of its high degree of identity (41.7%) and similarity (58.3%) to the overall amino acid sequence of hMTH1, including the Nudix box. CiMutT significantly suppressed the mutator activity of E. coli mutT mutant. Purified CiMutT had a pyrophosphohydrolase activity that hydrolyzed 8-oxo-dGTP to 8-oxo-dGMP and inorganic pyrophosphate. It had a pH optimum of 9.5 and Mg⁺⁺ requirement with optimal activity at 5 mM. The activity of CiMutT for 8-oxo-dGTP was comparable to that of hMTH1, while it was 100-fold lower for 2-oxo-dATP than that of hMTH1. These facts indicate that CiMutT is a functional homologue of E. coli MutT. In addition, the enzyme hydrolyzed all four of the unoxidized nucleoside triphosphates, with a preference for dATP. The specific activity for 8-oxo-dGTP was greater than that for unoxidized dATP and dGTP. These results suggest that CiMutT has the potential to prevent mutations by 8-oxo-dGTP in C. intestinalis.

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