Studies on transposition and dispersion of tandem repeat sequences (TrsA) in rice genome

我们这个项目的最终目标是阐明串联重复序列TRSA在水稻染色体上的分散机制。(1)转座参与了水稻基因组中串联重复序列(Trsa)的分散，我们用一对与trsAs杂交的引物和非trsA序列的侧翼进行了聚合酶链式反应，结果表明，TRSA序列位于两个独立的基因座trsA1和trsA2上，侧翼是染色体序列的长直接重复序列。这些结果可能支持这样的观点，即TRSA序列通过转座插入到每个基因座中，导致用作靶标的染色体序列重复。我们还发现trsA2上的靶序列特异地存在于水稻染色体中。克隆和测序发现，该序列是水稻…中一个新的反转录转座子重复序列更多染色体(2)利用FISH技术定位水稻染色体上的TRSA序列。在6、12号染色体长臂远端和5、7、8、9、10、11号染色体长臂远端检测到FISH信号。在非洲栽培稻中，在第5、6和7号染色体的长臂末端检测到了FISH信号。已知野生型水稻南方野生稻的TRSA拷贝数几乎是栽培稻的10倍。FISH分析表明，除12条染色体外，其余所有水稻染色体的长臂末端均检测到杂交信号。这些结果表明，TRSA在染色体上的数量和位置具有不同水稻品种的特点。值得注意的是，所有的信号都在染色体长臂的末端检测到，只有一条染色体(4号染色体到子午沙眼)除外。这些结果表明，染色体具有极性，这可能在染色体采集中发挥重要作用。较少

Our final goal of this project is to elucidate the dispersion mechanism of the tandem repeat sequences, TrsA,on rice chromosomes. The results we obtained in the past two years can be summarized as follows :(1) Involvement of transposition in dispersion of tandem repeat sequences (TrsA) in rice genome.We carried out PCR using a pair of primers that hybridize to TrsAs and flanking non-TrsA sequences, and obtained the results suggesting that TrsA sequences present at two independent loci, trsAl and trsA2, are flanked by long direct repeats of chromosomal sequences. These results may support the idea that the TrsA sequences have been inserted into each locus by transposition, resulting in duplication of chromosomal sequence used as target. We also found that the target sequence at trsA2 was present specifically in the indica rice chromosomes. Cloning and sequencing the target site of 440 bp at trsA2 revealed that this sequence was an LTR sequence of a novel retrotransposon repeated in rice … More chromosomes(2) Mapping of TrsA sequences on rice chromosomes by FISH.We mapped the TrsA sequences on the somatic prometaphase chromosomes of two O.sativa cultivars by using an improved FISH method. The FISH signals were detected at the distal ends of long arms of chromosome 6 and 12 in the japonica rice and at the distal ends of long arms of chromosome 5,7,8,9,10, and 11 in indica rice. In O.glaberrima, an African cultivated rice, the FISH signals were detected at the distal ends of long arms of chromosome 5,6 and 7. It has been known that the copy numbers of TrsA in O.meridionalis, a wild type rice, are almost ten times higher than those in O.sativa. FISH analysis showed that the hybridization signals were detected at the distal ends of long arms of all the chromosomes except 12. These results suggest that the numbers and locations of the TrsA on the chromosomes are characteristic to each rice species. It should be noticed that all the signals were detected at the distal ends of long arms of chromosomes except one (chromosome 4 to O.meridionalis). These results indicate that chromosomes have polarity which may play an important role in gathering chromosomes. Less