Department of Ecology and Evolution, University of Lausanne, Lausanne, 1015, Switzerland.
BMC Genomics. 2024 Sep 20;25(1):888. doi: 10.1186/s12864-024-10770-9.
Arbuscular mycorrhizal fungi (AMF) form mutualistic partnerships with approximately 80% of plant species. AMF, and their diversity, play a fundamental role in plant growth, driving plant diversity, and global carbon cycles. Knowing whether AMF are sexual or asexual has fundamental consequences for how they can be used in agricultural applications. Evidence for and against sexuality in the model AMF, Rhizophagus irregularis, has been proposed. The discovery of a putative mating-type locus (MAT locus) in R. irregularis, and the previously suggested recombination among nuclei of a dikaryon R. irregularis isolate, potentially suggested sexuality. Unless undergoing frequent sexual reproduction, evolution of MAT-locus diversity is expected to be very low. Additionally, in sexual species, MAT-locus evolution is decoupled from the evolution of arbitrary genome-wide loci.
We studied MAT-locus diversity of R. irregularis. This was then compared to diversification in a phosphate transporter gene (PTG), that is not involved in sex, and to genome-wide divergence, defined by 47,378 single nucleotide polymorphisms. Strikingly, we found unexpectedly high MAT-locus diversity indicating that either it is not involved in sex, or that AMF are highly active in sex. However, a strongly congruent evolutionary history of the MAT-locus, PTG and genome-wide arbitrary loci allows us to reject both the hypothesis that the MAT-locus is involved in mating and that the R. irregularis lineage is sexual.
Our finding shapes the approach to developing more effective AMF strains and is highly informative as it suggests that introduced strains applied in agriculture will not exchange DNA with native populations.
丛枝菌根真菌（AMF）与大约 80%的植物物种形成共生关系。AMF 及其多样性在植物生长、驱动植物多样性和全球碳循环中发挥着基础性作用。了解 AMF 是否具有有性或无性生殖，对于它们在农业应用中的使用方式具有根本影响。在模式 AMF 泡囊丛枝菌（Rhizophagus irregularis）中，已经提出了有性和无性生殖的证据。在 R. irregularis 中发现了一个假定的交配型基因座（MAT 基因座），以及之前在 R. irregularis 二倍体核之间的重组，这可能表明存在有性生殖。除非频繁进行有性生殖，否则 MAT 基因座多样性的进化预计非常低。此外，在有性物种中，MAT 基因座的进化与任意基因组范围内基因座的进化是解耦的。
我们研究了 R. irregularis 的 MAT 基因座多样性。然后将其与磷酸盐转运蛋白基因（PTG）的多样化进行比较，PTG 不参与性，与不涉及性的基因组广泛分化进行比较，由 47378 个单核苷酸多态性定义。令人惊讶的是，我们发现了出乎意料的高 MAT 基因座多样性，这表明它要么不参与性，要么 AMF 在性方面非常活跃。然而，MAT 基因座、PTG 和基因组广泛的任意基因座的强烈一致的进化历史使我们能够拒绝 MAT 基因座参与交配和 R. irregularis 谱系有性生殖的假说。
我们的发现改变了开发更有效的 AMF 菌株的方法，并且非常有启发性，因为它表明在农业中应用的引入菌株不会与本地种群交换 DNA。
