Giese H, Lyngkjaer M F, Stummann B M, Grell M N, Christiansen S K
Department of Ecology, Section of Genetics and Microbiology, Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, Frederiksberg C, 1871 Copenhagen, Denmark.
Mol Genet Genomics. 2003 Aug;269(5):699-705. doi: 10.1007/s00438-003-0876-5. Epub 2003 Jun 28.
A linear plasmid is widespread among isolates of the obligate biotrophic fungus Blumeria graminis f.sp. hordei (synonym Erysiphe graminis) (Bgh), the organism that causes the disease powdery mildew on barley. We cloned and sequenced the entire plasmid of 7965 bp. The plasmid contains two identical terminal inverted repeats (TIR) of 610 bp. Two ORFs are present on opposite strands, one encoding a phage-type DNA polymerase and the other a phage-type RNA polymerase. Two large transcripts of approximately 4.2 and 5.6 kb were identified in conidia, germinating conidia and Bgh -infected barley leaves, indicating that the polymerases are transcribed at most stages of the lifecycle. The transcription start sites were localised within the TIR regions, where a putative 11-bp ARS consensus sequence was also identified. To follow the sexual transmission of the plasmid we screened 27 Bgh isolates for mitochondrial polymorphisms. One polymorphism allowed us to carry out a cross between two isolates that differed in both mitochondrial genotype and presence/absence of the Bgh plasmid. The plasmid was transmitted independently of the origin of the mitochondria. No transfer of the plasmid was observed between two Bgh isolates that were co-cultivated for 1.5 years on a common susceptible barley variety. The plasmid appears to be an autonomous replicon with no phenotypic effect on Bgh.
一种线性质粒在大麦白粉病菌（Blumeria graminis f.sp. hordei，同义词为Erysiphe graminis，简称Bgh）的分离菌株中广泛存在，该病菌可引发大麦白粉病。我们克隆并测序了这个7965 bp的完整质粒序列。该质粒含有两个610 bp的相同末端反向重复序列（TIR）。两条互补链上各有一个开放阅读框（ORF），一个编码噬菌体类型的DNA聚合酶，另一个编码噬菌体类型的RNA聚合酶。在分生孢子、正在萌发的分生孢子以及被Bgh感染的大麦叶片中，鉴定出了两条大约4.2 kb和5.6 kb的大转录本，这表明在生命周期的大多数阶段，这些聚合酶都在转录。转录起始位点位于TIR区域内，在该区域还鉴定出了一个推测的11 bp的自主复制序列（ARS）共有序列。为了追踪该质粒的有性传播，我们对27个Bgh分离菌株进行了线粒体多态性筛选。一种多态性使我们能够在两个线粒体基因型以及是否存在Bgh质粒都不同的分离菌株之间进行杂交。该质粒的传播独立于线粒体的来源。在一个共同的感病大麦品种上共同培养1.5年的两个Bgh分离菌株之间未观察到质粒的转移。该质粒似乎是一个自主复制子，对Bgh没有表型影响。
