Conlon Benjamin H, Gostinčar Cene, Fricke Janis, Kreuzenbeck Nina B, Daniel Jan-Martin, Schlosser Malte S L, Peereboom Nils, Aanen Duur K, de Beer Z Wilhelm, Beemelmanns Christine, Gunde-Cimerman Nina, Poulsen Michael
Section for Ecology and Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark.
Department of Biology, Biotechnical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia.
iScience. 2021 Jun 1;24(6):102680. doi: 10.1016/j.isci.2021.102680. eCollection 2021 Jun 25.
Insights into the genomic consequences of symbiosis for basidiomycete fungi associated with social insects remain sparse. Capitalizing on viability of spores from centuries-old herbarium specimens of free-living, facultative, and specialist termite-associated fungi, we obtained genomes of 10 specimens, including two type species described by Linnaeus >240 years ago. We document that the transition to termite association was accompanied by significant reductions in genome size and gene content, accelerated evolution in protein-coding genes, and reduced functional capacities for oxidative stress responses and lignin degradation. Functional testing confirmed that termite specialists perform worse under oxidative stress, while all lineages retained some capacity to cleave lignin. Mitochondrial genomes of termite associates were significantly larger; possibly driven by smaller population sizes or reduced competition, supported by apparent loss of certain biosynthetic gene clusters. Our findings point to relaxed selection that mirrors genome traits observed among obligate endosymbiotic bacteria of many insects.
对于与社会性昆虫相关的担子菌纲真菌而言，共生在基因组层面产生的影响仍鲜为人知。我们利用来自数百年前植物标本馆标本的自由生活、兼性和专性白蚁相关真菌孢子的活力，获得了10个标本的基因组，其中包括240多年前由林奈描述的两个模式种。我们记录到，向白蚁共生的转变伴随着基因组大小和基因含量的显著减少、蛋白质编码基因的加速进化，以及氧化应激反应和木质素降解功能能力的降低。功能测试证实，白蚁专性真菌在氧化应激下表现较差，而所有谱系仍保留了一定的木质素裂解能力。白蚁共生真菌的线粒体基因组明显更大；这可能是由较小的种群规模或竞争减少所驱动，某些生物合成基因簇的明显缺失也支持了这一点。我们的研究结果表明，选择压力有所放松，这与许多昆虫专性内共生细菌中观察到的基因组特征相似。
