Naito Mizue, Pawlowska Teresa E
Graduate Field of Microbiology, Cornell University, Ithaca, New York, USA.
School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, New York, USA
mBio. 2016 Jun 21;7(3):e02057-15. doi: 10.1128/mBio.02057-15.
Heritable endobacteria, which are transmitted from one host generation to the next, are subjected to evolutionary forces that are different from those experienced by free-living bacteria. In particular, they suffer consequences of Muller's ratchet, a mechanism that leads to extinction of small asexual populations due to fixation of slightly deleterious mutations combined with the random loss of the most-fit genotypes, which cannot be recreated without recombination. Mycoplasma-related endobacteria (MRE) are heritable symbionts of fungi from two ancient lineages, Glomeromycota (arbuscular mycorrhizal fungi) and Mucoromycotina Previous studies revealed that MRE maintain unusually diverse populations inside their hosts and may have been associated with fungi already in the early Paleozoic. Here we show that MRE are vulnerable to genomic degeneration and propose that they defy Muller's ratchet thanks to retention of recombination and genome plasticity. We suggest that other endobacteria may be capable of raising similar defenses against Muller's ratchet.
可遗传的内共生菌会从一代宿主传递到下一代，它们所经历的进化力量与自由生活的细菌不同。特别是，它们会受到穆勒棘轮效应的影响，这是一种机制，由于轻微有害突变的固定以及最适应基因型的随机丢失，导致小型无性繁殖种群灭绝，而没有重组就无法重新创造出最适应的基因型。支原体相关内共生菌（MRE）是来自两个古老谱系（球囊菌门（丛枝菌根真菌）和毛霉亚门）真菌的可遗传共生体。先前的研究表明，MRE在其宿主内维持着异常多样的种群，并且可能在早古生代就已与真菌相关联。在这里，我们表明MRE易受基因组退化的影响，并提出它们由于保留了重组和基因组可塑性而能抵御穆勒棘轮效应。我们认为其他内共生菌可能也有能力对穆勒棘轮效应提出类似的防御。
