Evidence of non-tandemly repeated rDNAs and their intragenomic heterogeneity in<i>Rhizophagus irregularis</i>

<jats:title>Abstract</jats:title><jats:p>Arbuscular mycorrhizal fungus (AMF) species are one of the most widespread symbionts of land plants. Our substantially improved reference genome assembly of a model AMF,<jats:italic>Rhizophagus irregularis</jats:italic>DAOM-181602 (total contigs = 210), facilitated discovery of repetitive elements with unusual characteristics.<jats:italic>R. irregularis</jats:italic>has only ten or eleven copies of complete 45S rDNAs, whereas the general eukaryotic genome has tens to thousands of rDNA copies.<jats:italic>R. irregularis</jats:italic>rDNAs are highly heterogeneous and lack a tandem repeat structure. These findings provide evidence for the hypothesis that rDNA heterogeneity depends on the lack of tandem repeat structures. RNA-Seq analysis confirmed that all rDNA variants are actively transcribed. Observed rDNA/rRNA polymorphisms may modulate translation by using different ribosomes depending on biotic and abiotic interactions. The non-tandem repeat structure and intragenomic heterogeneity of AMF rDNA/rRNA may facilitate adaptation to a various environmental condition including the broad host range.</jats:p>