Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands.
PLoS One. 2022 Jul 1;17(7):e0270481. doi: 10.1371/journal.pone.0270481. eCollection 2022.
Arbuscular mycorrhizal fungi (AMF) are part of the most widespread fungal-plant symbiosis. They colonize at least 80% of plant species, promote plant growth and plant diversity. These fungi are multinucleated and contain either one or two haploid nuclear genotypes (monokaryon and dikaryon) identified by the alleles at a putative mating-type locus. This taxon has been considered as an ancient asexual scandal because of the lack of observable sexual structures. Despite identification of a putative mating-type locus and functional activation of genes related to mating when two isolates co-exist, it remains unknown if the AMF life cycle involves a sexual or parasexual stage. We used publicly available genome sequences to test if Rhizophagus irregularis dikaryon genomes display signatures of sexual reproduction in the form of reciprocal recombination patterns, or if they display exclusively signatures of parasexual reproduction involving gene conversion. We used short-read and long-read sequence data to identify nucleus-specific alleles within dikaryons and then compared them to orthologous gene sequences from related monokaryon isolates displaying the same putative MAT-types as the dikaryon. We observed that the two nucleus-specific alleles of the dikaryon A5 are more related to the homolog sequences of monokaryon isolates displaying the same putative MAT-type than between each other. We also observed that these nucleus-specific alleles displayed reciprocal recombination signatures. These results confirm that dikaryon and monokaryon isolates displaying the same putative MAT-type are related in their life-cycle. These results suggest that a genetic exchange mechanism, involving reciprocal recombination in dikaryon genomes, allows AMF to generate genetic diversity.
丛枝菌根真菌 (AMF) 是最广泛的真菌-植物共生体的一部分。它们至少可以定殖 80%的植物物种，促进植物生长和植物多样性。这些真菌是多核的，含有一个或两个单倍体核基因型（单核体和双核体），由假定的交配型位点的等位基因识别。由于缺乏可观察的有性结构，该分类群被认为是古老的无性丑闻。尽管在两个分离物共存时鉴定了假定的交配型位点和与交配相关的基因的功能激活，但仍不清楚 AMF 的生命周期是否涉及有性或准性阶段。我们使用公开可用的基因组序列来测试 Rhizophagus irregularis 双核体基因组是否以相互重组模式显示有性生殖的特征，或者它们是否仅显示涉及基因转换的准性生殖的特征。我们使用短读和长读序列数据来识别双核体中的核特异性等位基因，然后将它们与显示与双核体相同假定 MAT 类型的相关单核体分离物的同源基因序列进行比较。我们观察到双核体 A5 的两个核特异性等位基因与显示相同假定 MAT 类型的单核体分离物的同源序列更相关，而不是彼此之间。我们还观察到这些核特异性等位基因显示相互重组的特征。这些结果证实了显示相同假定 MAT 类型的双核体和单核体分离物在其生命周期中是相关的。这些结果表明，涉及双核体基因组中相互重组的遗传交换机制允许 AMF 产生遗传多样性。
