Arbuscular mycorrhizal fungi (AMF) are of great ecological importance because of their effects on plant growth. Closely related genotypes of the same AMF species coexist in plant roots. However, almost nothing is known about the molecular interactions occurring during such coexistence. We compared in planta AMF gene transcription in single and coinoculation treatments with two genetically different isolates of Rhizophagus irregularis in symbiosis independently on three genetically different cassava genotypes. Remarkably few genes were specifically upregulated when the two fungi coexisted. Strikingly, almost all of the genes with an identifiable putative function were known to be involved in mating in other fungal species. Several genes were consistent across host plant genotypes but more upregulated genes involved in putative mating were observed in host genotype (COL2215) compared with the two other host genotypes. The AMF genes that we observed to be specifically upregulated during coexistence were either involved in the mating pheromone response, in meiosis, sexual sporulation or were homologs of MAT-locus genes known in other fungal species. We did not observe the upregulation of the expected homeodomain genes contained in a putative AMF MAT-locus, but observed upregulation of HMG-box genes similar to those known to be involved in mating in Mucoromycotina species. Finally, we demonstrated that coexistence between the two fungal genotypes in the coinoculation treatments explained the number of putative mating response genes activated in the different plant host genotypes. This study demonstrates experimentally the activation of genes involved in a putative mating response and represents an important step towards the understanding of coexistence and sexual reproduction in these important plant symbionts.

丛枝菌根真菌（AMF）因其对植物生长的影响而具有重要的生态意义。同一 AMF 物种的密切相关基因型共存于植物根中。然而，对于这种共存期间发生的分子相互作用几乎一无所知。我们比较了两种遗传不同的不规则根噬菌分离株在三种遗传不同的木薯基因型上独立共生的单一接种和共接种处理中的植物AMF 基因转录。当两种真菌共存时，很少有基因被特异性上调。引人注目的是，几乎所有具有可识别推定功能的基因都与其他真菌物种的交配有关。一些基因在宿主植物基因型中是一致的，但与其他两种宿主基因型相比，在宿主基因型（COL2215）中观察到更多参与推定交配的上调基因。我们观察到在共存期间特异性上调的 AMF 基因要么参与交配信息素反应、减数分裂、有性孢子形成，要么是其他真菌物种中已知的 MAT 位点基因的同源物。我们没有观察到假定的 AMF MAT 位点中包含的预期同源域基因的上调，但观察到与已知参与毛霉菌亚门交配的基因类似的 HMG-box 基因的上调。最后，我们证明了两种真菌基因型在共接种处理中的共存解释了在不同植物宿主基因型中激活的推定交配反应基因的数量。 这项研究通过实验证明了参与假定交配反应的基因的激活，并代表着朝着理解这些重要植物共生体的共存和有性繁殖迈出的重要一步。