Varassas Stylianos P, Kouvelis Vassili N
Department of Genetics and Biotechnology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece.
Front Microbiol. 2022 Mar 21;13:821638. doi: 10.3389/fmicb.2022.821638. eCollection 2022.
Entomopathogenic fungi and more specifically genera and have been exploited for the biological control of pests. Genome analyses are important to understand better their mode of action and thus, improve their efficacy against their hosts. Until now, the sequences of their mitochondrial genomes were studied, but not at the level of transcription. Except of yeasts and , whose mt gene transcription is well described, in all other Ascomycota, i.e., Pezizomycotina, related information is extremely scarce. In this work, mt transcription and key enzymes of this function were studied. RT-PCR experiments and Northern hybridizations reveal the transcriptional map of the mt genomes of and species. The mt genes are transcribed in six main transcripts and undergo post-transcriptional modifications to create single gene transcripts. Promoters were determined in both mt genomes with a comparative analysis, including all known information from other fungal mt genomes. The promoter consensus sequence is 5'-ATAGTTATTAT-3' which is in accordance with the definition of the polycistronic transcripts determined with the experiments described above. Moreover, 5'-RACE experiments in the case of premature polycistronic transcript 1-4-8-6 revealed the 5' end of the RNA transcript immediately after the determined promoter, as also found in other fungal species. Since several conserved elements were retrieved from these analyses compared to the already known data from yeasts and , the phylogenetic analyses of mt RNA polymerase (Rpo41) and its transcriptional factor (Mtf1) were performed in order to define their evolution. As expected, it was found that fungal Rpo41 originate from the respective polymerase of T7/T3 phages, while the ancestor of Mtf1 is of alpha-proteobacterial origin. Therefore, this study presents insights about the fidelity of the mt single-subunit phage-like RNA polymerase during transcription, since the correct identification of mt promoters from Rpo41 requires an ortholog to bacterial sigma factor, i.e., Mtf1. Thus, a previously proposed hypothesis of a phage infected alpha-proteobacterium as the endosymbiotic progenitor of mitochondrion is confirmed in this study and further upgraded by the co-evolution of the bacterial (Mtf1) and viral (Rpo41) originated components in one functional unit.
昆虫病原真菌，尤其是某些属的真菌，已被用于害虫的生物防治。基因组分析对于更好地理解它们的作用模式从而提高其对宿主的防治效果至关重要。到目前为止，人们对它们线粒体基因组的序列进行了研究，但尚未涉及转录水平。除了酵母和某些物种，其线粒体基因转录已有详细描述外，在所有其他子囊菌门，即粪壳菌纲中，相关信息极为稀少。在这项工作中，对线粒体转录及其关键酶进行了研究。逆转录聚合酶链反应（RT-PCR）实验和Northern杂交揭示了相关物种线粒体基因组的转录图谱。线粒体基因转录为六个主要转录本，并经历转录后修饰以产生单基因转录本。通过比较分析在两个线粒体基因组中确定了启动子，该分析包括来自其他真菌线粒体基因组的所有已知信息。启动子共有序列为5'-ATAGTTATTAT-3'，这与上述实验确定的多顺反子转录本的定义一致。此外，对于早熟多顺反子转录本1-4-8-6的5'-末端快速扩增（5'-RACE）实验揭示了RNA转录本的5'末端紧接在确定的启动子之后，这在其他真菌物种中也有发现。由于与酵母和某些物种的已知数据相比，从这些分析中检索到了几个保守元件，因此对线粒体RNA聚合酶（Rpo41）及其转录因子（Mtf1）进行了系统发育分析以确定它们的进化。正如预期的那样，发现真菌Rpo41起源于T7/T3噬菌体的相应聚合酶，而Mtf1的祖先起源于α-变形菌。因此，这项研究揭示了线粒体单亚基噬菌体样RNA聚合酶在转录过程中的保真度，因为从Rpo41正确识别线粒体启动子需要一个与细菌σ因子直系同源的蛋白，即Mtf1。因此，本研究证实了先前提出的关于噬菌体感染的α-变形菌作为线粒体共生祖先的假说，并通过细菌（Mtf1）和病毒（Rpo41）起源成分在一个功能单元中的共同进化进一步完善了该假说。
