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Science, Japan

Ikeda Y.,GCOE Research Group | Ikeda Y.,French Institute of Health and Medical Research
Plant and Cell Physiology

Genomic imprinting is an epigenetic phenomenon found in mammals and flowering plants that leads to differential allelic gene expression depending on their parent of origin. In plants, genomic imprinting primarily occurs in the endosperm, and it is associated with seed development. The imprinted expression is driven by the epigenetic memory programmed in each lineage of female and male germlines. Several imprinted genes have been identified based on genetic studies in maize and Arabidopsis. Recent advances in genome-wide analyses made it possible to identify multiple imprinted genes including many nuclear proteins, such as transcription factors and chromatin-related proteins in different plant species. Some of these genes are conserved in Arabidopsis, rice and maize, but many are species specific. Genome-wide analyses also clarified the regulation mechanism of imprinted genes orchestrated by DNA methylation and histone methylation marks. Additionally, genetic analyses using Arabidopsis revealed new regulatory factors of DNA demethylation and imprinting and shed light on the more precise mechanisms. © 2012 The Author. Source

Craven M.J.,University of Abertay Dundee | Jimbo H.C.,GCOE Research Group
Groups, Complexity, Cryptology

We consider the multiple conjugacy search problem over a subclass of partially commutative groups and experimentally attack it with a genetic algorithm hybridised with a "length attack". We detail symbolic computation of words over the groups, constructing functions which measure certain statistics of those words. By experimentation, the hybrid algorithm is shown to be effective, showing that the standard conjugacy search problem is harder than the multiple conjugacy search problem for our groups. Moreover, some intuitive methods of increasing problem difficulty are overcome by the algorithm, and in fact make the problem easier to solve. We show our algorithm is efficient, comparing well with traditional approaches in groups that are statistically similar. Finally, via "approximation" of braid groups by our subclass, we consider implications of the attack on certain cryptosystems, pointing to further work in the discipline of group-theoretic cryptography. © 2012 by Walter de Gruyter Berlin Boston. Source

Ohnishi T.,GCOE Research Group | Yoshino M.,GCOE Research Group | Yamakawa H.,Japan National Agricultural Research Center | Kinoshita T.,GCOE Research Group
Plant and Cell Physiology

Oryza sativa is widely used as a model organism for many aspects of research in monocots and cereals. However, it has certain disadvantages as a model species compared with Arabidopsis thaliana, the eudicot species most widely used in plant sciences: first, it has a long cultivation time; and second, it requires considerably more space for growth. Here, we introduce a biotron breeding system, which allows rapid and reliable rice cultivation using a well-equipped artificial environmental chamber. This system involves use of regulation of CO 2 levels, removal of tillers and embryo rescue to overcome the disadvantages of rice cultivation. The rice cultivars Nipponbare, Koshihikari, Taichung 65 and Kasalath all showed vigorous growth and sufficient seed production in the biotron breeding system with accelerated flowering time. Nipponbare, which was the earliest among these cultivars, flowered at about 50 d after sowing. The life cycle of these plants could be further shortened using an embryo rescue technique on immature seeds at 7 d after pollination, thereby avoiding the lengthy process of seed maturation. Overall, it was possible to shorten the life cycle of Nipponbare to about 2 months under the controlled conditions. Furthermore, controlled crosses, which can be difficult with conventional cultivation methods, were easy to perform as we could control the exact timing of anther dehiscence. Thus, our biotron breeding system offers a valuable new approach to genetic and breeding studies in rice. © 2011 The Author. Source

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