| Summary: | 碩士 === 國立臺灣大學 === 植物病理學研究所 === 90 === A wide variety of organisms have retrotransposons present in the genome, and it is the same in the genome of Phytophthora parasitica, a phytopathogenic fungus. PARTN1 was one retrotransposon found in the genome of P. parasitica, and another one (PARTN1h) in this study was found to be nearly identical to PARTN1. They shared many similarities including genome structure and arrangement (Ty1-copia retrotransposons), nucleotide identity 96.5%, and conserved domains in polyprotein. In both genomes of PARTN1 and PARTN1h, many stop codons were found, and it showed that they were inactive copies in the genome.
Our study was trying to find out if there was any characteristic in the insertion site of PARTN1 retrotransposon. From 12 phage clones analyzed, 7 showed that PARTN1 had a preferential tendency to insert into retrotransposons, including itself. It is also been found in the case of BARE, a retrotransposon in barley, Skipper of Dictyostelium, and Zdel and Opie of maize. Retrotransposons choosing to insert into retroelements could avoid generating mutations in the genome of hosts, thus natural selection might act on host factors to favor such an insertion on retrotransposons. One clone was found the preference of PARTN1 in insertion was to transposon, and the same selection forces mentioned above could have taken place in this case.
From the results of insertion site of PARTN1, target site duplication (TAT) was seen in 4 clones. There were another 4 clones with only one flanking region sequenced also had these three codons TAT present in flanking side. It has been reported that MAGGY, a retrotransposon in Magnaporthe grisea, targets in AT-rich region. In our study, it showed similar result. However, there were two extra codons, GT, found between sequences of LTR and TSD in clones 7-5 and 8-1. It was not sure whether their TSD did contain 5 codons, GTTAT, or not because only one flanking side was sequenced out or these two extra codons did exist on one flanking side only. It needs further information to be able to give an assumption on it.
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