Reciprocal recombination reflects sexual reproduction in symbiotic arbuscular mycorrhizal fungi

Abstract

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 display either one or two nucleus genotypes (monokaryon and dikaryon) determined by a putative mating-type locus. This taxon has been considered as an ancient asexual scandal because of the lack of observable sexual structures. Despite the identification of a putative mating-type (MAT-type) locus and the functional activation of genes related to mating when two isolates co-exist, it is still unknown if AMF display a sexual or a parasexual life cycle. To test if AMF genomes display signatures of a sexual life-cycle involving the putative MAT-locus, we used publicly available genome sequences to test if recombining nucleotype-specific haplotypes could be identified using short-read Illumina sequences. We identified nucleus genotype-specific haplotypes within dikaryons and compared them to orthologous gene sequences from related monokaryon isolates displaying similar putative MAT-types. We show that haplotypes within a dikaryon isolate are more similar to homologue sequences of isolates having the same MAT-type than among them. We demonstrate that these genotype-specific haplotypes are recombinant, and are not consistently most similar to the monokaryon isolate sharing the same mating-type allele. These results are consistent with a sexual origin of the dikaryon rather than a parasexual origin and provides an important step to understand the life cycle of these globally important symbiotic fungi.

Unraveling the genetic diversity and evolution of Arbuscular Mycorrhizal Fungi (AMF)

“…The researchers conducted a comparison of various isolates of AMF with similar putative mat-types, which are genes responsible for mating compatibility. They observed that isolates sharing putative mat-types exhibited similarities in their life-cycle, implying the involvement of a genetic exchange mechanism [24]. The findings have substantial implications for our comprehension of AMF biology and evolution.…”

“…Found that a genetic exchange mechanism involves reciprocal recombination in AMF genomes [24] Established 19 fungal genes transferred between fungi and bacterial plants [25] These network characteristics foster mutual reliance and equilibrium within ecosystems. The high level of connectance ensures the efficient exchange of nutrients between plants and AMF, thereby enhancing their mutualistic relationship.…”

“…In the study conducted by Mateus et al, publicly accessible genome sequences were utilized to examine whether AMF (arbuscular mycorrhizal fungi) genomes demonstrate indications of sexual or parasexual reproduction. The study's findings showed a close relationship in the life-cycle of dikaryon and monokaryon isolates with the same putative mattype, suggesting a genetic exchange mechanism involving reciprocal recombination in AMF genomes [24] [Table 1]. AMF consist of a range of fungi that form mutually beneficial relationships with the roots of most land-dwelling plants.…”