Nakayashiki H, Ikeda K, Hashimoto Y, Tosa Y, Mayama S
Laboratory of Plant Pathology, Faculty of Agriculture, Kobe University, Kobe, 657-8501, Japan.
Nucleic Acids Res. 2001 Mar 15;29(6):1278-84. doi: 10.1093/nar/29.6.1278.
We have introduced the LTR-retrotransposon MAGGY into a naive genome of Magnaporthe grisea and estimated the copy number of MAGGY in a cell by serial isolation of fungal protoplasts at certain time intervals. The number of MAGGY elements rapidly increased for a short period following introduction. However, it did not increase geometrically and reached equilibrium at 20-30 copies per genome, indicating that MAGGY was repressed or silenced during proliferation. De novo methylation of MAGGY occurred immediately following invasion into the genome but the degree of methylation was constant and did not correlate with the repression of MAGGY. 5-Azacytidine treatment demethylated and transcriptionally activated the MAGGY element in regenerants but did not affect transpositional frequency, suggesting that post-transcriptional suppression, not methylation, is the main force that represses MAGGY proliferation in M.grisea. Support for this conclusion was also obtained by examining the methylation status of MAGGY sequences in field isolates of M.grisea with active or inactive MAGGY elements. Methylation of the MAGGY sequences was detected in some isolates but not in others. However, the methylation status did not correlate with the copy numbers and activity of the elements.
我们已将LTR逆转座子MAGGY导入稻瘟病菌的原始基因组，并通过在特定时间间隔连续分离真菌原生质体来估算细胞中MAGGY的拷贝数。导入后，MAGGY元件的数量在短时间内迅速增加。然而，它并非呈几何级数增加，而是在每个基因组达到20 - 30个拷贝时达到平衡，这表明MAGGY在增殖过程中受到抑制或沉默。MAGGY在侵入基因组后立即发生从头甲基化，但甲基化程度保持不变，且与MAGGY的抑制无关。5-氮杂胞苷处理使再生体中的MAGGY元件去甲基化并转录激活，但不影响转座频率，这表明转录后抑制而非甲基化是抑制稻瘟病菌中MAGGY增殖的主要力量。通过检测具有活跃或不活跃MAGGY元件的稻瘟病菌田间分离株中MAGGY序列的甲基化状态，也获得了对这一结论的支持。在一些分离株中检测到了MAGGY序列的甲基化，但在其他分离株中未检测到。然而，甲基化状态与元件的拷贝数和活性无关。
