Activation and epigenetic regulation of DNA transposon nDart1 in rice

• Published in: Plant and cell physiology 2012-05, Vol.53 (5), p.857-868
• Main Authors: Eun, Chang-Ho, Takagi, Kyoko, Park, Kyeung-Il, Maekawa, Masahiko, Iida, Shigeru, Tsugane, Kazuo
• Format: Article
• Language: English
• Subjects: Azacitidine - pharmacology; Azacytidine; chromosome 6; Conserved sequence; Cytosine; DNA methylation; DNA Methylation - drug effects; DNA Methylation - genetics; DNA Transposable Elements - genetics; DNA, Plant - genetics; Epigenesis, Genetic - drug effects; epigenetics; Gene Expression Regulation, Plant - drug effects; Genes, Plant - genetics; genomics; Hydroxamic Acids - pharmacology; Insertion; Long interspersed nucleotide elements; Mutation - genetics; Oryza - drug effects; Oryza - genetics; Oryza sativa; Promoters; Seeds - drug effects; Seeds - genetics; Sequence Analysis, DNA; Somaclonal variation; transposase; transposase gene; Transposases - genetics; Transposases - metabolism; Transposition; Transposons
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcs060

A large part of the rice genome is composed of transposons. Since active excision/reintegration of these mobile elements may result in harmful genetic changes, many transposons are maintained in a genetically or epigenetically inactivated state. However, some non-autonomous DNA transposons of the nDart1-3 subgroup, including nDart1-0, actively transpose in specific rice lines, such as pyl-v which carries an active autonomous element, aDart1-27, on chromosome 6. Although nDart1-3 subgroup elements show considerable sequence identity, they display different excision frequencies. The most active element, nDart1-0, had a low cytosine methylation status. The aDart1-27 sequence showed conservation between pyl-stb (pyl-v derivative line) and Nipponbare, which both lack autonomous activity for transposition of nDart1-3 subgroup elements. In pyl-v plants, the promoter region of the aDart1-27 transposase gene was more hypomethylated than in other rice lines. Treatment with the methylation inhibitor 5-azacytidine (5-azaC) induced transposition of nDart1-3 subgroup elements in both pyl-stb and Nipponbare plants; the new insertion sites were frequently located in genic regions. 5-AzaC treatment principally induced expression of Dart1-34 transposase rather than the other 38 aDart1-related elements in both pyl-stb and Nipponbare treatment groups. Our observations show that transposition of nDart1-3 subgroup elements in the nDart1/aDart1 tagging system is correlated with the level of DNA methylation. Our system does not cause somaclonal variation due to an absence of transformed plants, offers the possibility of large-scale screening in the field and can identify dominant mutants. We therefore propose that this tagging system provides a valuable addition to the tools available for rice functional genomics.