Analysis of transposition mechanisms of the active transposon firstly identified in rice

用伽玛射线辐照诱导金伯祖种子获得一个细长变异体突变体（品系：IM294）。这种突变性状是由一个隐性突变基因控制的，尽管反复自繁殖，但从未固定过。我们之前的研究表明，这种突变是由于精确切除了插入野生型等位基因Rurm1（水稻泛素相关修饰因子1）位点的一个微型倒置重复转座元件mPing而引起的。本研究证实了这一点，同时也表明缺少编码区的mPing是一个5.2 kb的元素Ping的缺失衍生物。在水稻基因组中，有一个与Ping相关的元素被命名为Pong。这两个元素都包含两个开放阅读框架（orf）。ORF1的功能是未知的，而ORF2被认为编码转座酶。比较了2个品种和IM294在6个mPing插入位点的切除频率。金宝祖和日本裸未发现切除，而IM294在两个地点观察到6例切除事件。这表明Rurm1的失活可能会影响mPing的转位活性。我们通过实时定量PCR检测了rumm1等位基因和Ping、Pong两个orf的转录活性，发现Ping orf和Pong ORF1的转录活性在IM294中显著增加。这表明rumm1 ^+抑制Ping和mPing的转录和扩增同时发生在金伯祖基因组中。伽马射线辐照显著增加了金伯祖基因组中Ping基因的拷贝数。这些结果表明，金伯祖的遗传背景和rumm1位点的罕见突变将为螨在几种生物中的扩增提供基础模型。

A mutable slender mutant (line : IM294) was induced with gamma-ray irradiation to seeds of the rice variety Gimbozu. This mutant character is governed by a recessive mutant gene and has never been fixed in spite of repeated self-propagation. Our previous study suggested that the mutability is caused by the precise excision of a MITE (Miniature Invereted-repeat Transposable Element mPing) that was inserted in the wild type allele at the Rurm1(Rice ubiquitin related modifier 1) locus. The present study confirmed this point, and also indicated that mPing, which lacks coding region, is a deletion derivative of a 5.2-kb element named Ping. There was a related element of Ping named Pong in the rice genom. Both elements contained two open reading frames(ORFs). The function of ORF1 is unknown, while the ORF2 is assumed to encode the transposase. The excision frequencies of mPing at six mPing insertion sites were compared among two varieties and IM294. No excision was found in Gimbozu and Nipponbare, while in IM294 six excision events were observed at the two sites. This indicates that the inactivation of Rurm1 might affect the transposition activity of mPing. We investigated transcription activities of Rurm1 alleles and the two ORFs of Ping and Pong by real time quantitative PCR and found that the activities of Ping ORFs and Pong ORF1 showed a significant increase in IM294. This suggests that Rurm1^+ inhibits the transcription and amplification of Ping and mPing occurred simultaneously in the Gimbozu genome. A gamma-ray irradiation significantly increased the copy number of Ping in the Gimbozu genome. These results indicate that Gimbozu genetic background and the rare mutation at the Rurm1 locus will provide a basic model for the amplification of MITE in several organisms.