|Budget Amount *help
¥16,100,000 (Direct Cost : ¥16,100,000)
Fiscal Year 2005 : ¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 2004 : ¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 2003 : ¥9,900,000 (Direct Cost : ¥9,900,000)
In plants, phenotypic variations have generally been found to be caused by genetic changes. However, it has recently been shown that phenotypic variations can also be potentially caused by epigenetic changes due to aberrant methylation states. Unlike that in mammalian genomes, DNA methylation in the plant genome was found to be heritably maintained during both meiotic and mitotic phases. Therefore, an altered methylation state in a plant genomic segment might be transmitted and maintained in the progeny. This study consists of two parts to identify presence of genetic segments with variable methylation state and to understand its mechanism. Firstly, we surveyed genomic segments that change methylation state among different nine rice strains including Japonica, Indica and wild rices. Second, we analyzed demethylation process in Antirrhinum transposon Tam3, of which activity is tightly controlled by temperature and appears to be correlated with its methylation state.
On the first issue, our results showed that the occurrence of epigenetic (epi)-markers in non-polymorphic fragments appeared to be correlated with the genetic distance between any two of the nine rice strains examined. In contrast, the proportion of epi-markers in the total number of fragments, including polymorphic and non-polymorphic fragments, was constant (2-3%) in all the pairs. We assume that the epigenetic differences in methylation among the rice genomes influence certain phenotypic variations.
On the second issue, we found that the methylation level of Tam3 in Antirrhinum is regulated by the Tam3 activity. It is the activity of Tam3, which is dependent on the ability of its transposase to bind DNA, which is affected by growing temperature and the methylation/demethylation of Tam3 is the consequence, not the cause, of transposition.