Nuclear Dynamics in the Arbuscular Mycorrhizal Fungi

Host identity influences nuclear dynamics in arbuscular mycorrhizal fungi

“…Our findings are based on very complex nuclear dynamics that involves thousands of nuclei coexisting and moving bi-directionally in hyphae and spores. 6,[27][28][29] Thus, this study reveals a remarkable orchestration of nuclear movements within cells, as necessary to produce spores with nuclei at a ratio of 1:1 or to ensure that one nucleotype always dominates another, depending on the strain or host identity. As we find no evidence that the two nucleotypes are in physical contact or fused with one another, as observed in other fungal dikaryons, 30 how this system functions in AMF is presently unclear.…”

“…1 Knowledge of even basic elements of AM fungal biology is still poor, with the discovery that AMF may in fact have a sexual life cycle being only very recently reported. [2][3][4][5] AMF produce asexual spores that contain up to several thousand individual haploid nuclei 6 of either largely uniform genotypes (AMF homokaryons) or nuclei originating from two parental genotypes [2][3][4][5] (AMF dikaryons or heterokaryons). In contrast to the sexual dikaryons in the phyla Ascomycota and Basidiomycota, 7,8 in which pairs of nuclei coexist in single hyphal compartments, AMF dikaryons carry several thousand nuclei in a coenocytic mycelium.…”

“…Arbuscular mycorrhizal fungi are highly unusual entities in which aseptate hyphae (also known as coenocytic mycelia, where the mycelium is continuous and considered as a single cell) and spores may encode tens of thousands of independent nuclei that are capable of bidirectional movement across a single organism. 6 The recent discovery that a subset of AMF strains carries a stable population of two divergent nucleotypes, each presumably originating from a ''parental'' strain, reconciles prevailing controversies and debate surrounding the genomic organization of these widespread plant symbionts while also providing compelling evidence that AMF may exist as dikaryotic organisms. 2,4 Until now, it was entirely unknown whether the multinucleate state of the AMF dikaryotic spores and mycelia results in (and from) random nuclear dynamics or whether the composition of the nucleotype population (i.e., total abundance and relative proportion of parental nucleotypes) is subject to active regulation and is responsive to environmental conditions.…”

“…It could, however, involve synchronous or parasynchronous mitotic divisions, something that has never been observed to date in AMF. 6 Fluorescence in situ hybridization (FISH) techniques may be useful in addressing this question and would be key to identify how nucleotypes are distributed spatially within the spores and mycelium of AMF dikaryons.…”

Global drivers of obligate mycorrhizal symbionts diversification

“…The species concept is difficult to apply in AMF, which are poorly differentiated morphologically and mainly characterized by environmental sequences [16]. In addition, their reproduction mode is not well known and they have unique nuclear dynamics in their spores and hyphae [61]. Our GMYC analyses suggest that biologically relevant AMF species-like units correspond to SSU rRNA haplotypes with a sequence similarity between 98.5 and 99%.…”