Homo- and Dikaryons of the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis Differ in Life History Strategy

Abstract

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that have the potential to improve crop yield. These multinucleate organisms are either “homokaryotic” or “dikaryotic”. In AMF dikaryons, thousands of nuclei originating from two parental strains coexist in the same cytoplasm. In other fungi, homokaryotic and dikaryotic strains show distinct life history traits (LHTs), such as variation in growth rates and fitness. However, how such traits compare between dikaryons and homokaryons of AMF is unknown. To address this, we measured 20 LHT of four dikaryons and five homokaryons of the model fungus Rhizophagus irregularis across root organ cultures of three host plants (carrot, chicory, and tobacco). Our analyses show that dikaryons have clearly distinct life history strategies (LHSs) compared to homokaryons. In particular, spores of homokaryons germinate faster and to a higher proportion than dikaryons, whereas dikaryons grow significantly faster and create a more complex hyphal network irrespective of host plant species. Our study links AMF nuclear status with key LHT with possible implications for mycorrhizal symbiotic functioning.

The effects of arbuscular mycorrhizal fungal species and taxonomic groups on stressed and unstressed plants: a global meta‐analysis

“…irregularis (Chen et al ., 2018; Serghi et al ., 2021) that may have consequences for the symbiotic functions of the fungus. For example, it has been shown that the proportion and speed of spore germination are higher in homokaryons, while the hyphal network structure is more complex in dikaryons (Serghi et al ., 2021). In any case, the physiological mechanisms underlying the differences between AMF species is an aspect of Glomeromycotan biology that requires further study.…”

“…Other efforts aimed to disentangle the genetic basis of intra‐specific trait variability of R . irregularis (Chen et al ., 2018; Serghi et al ., 2021) that may have consequences for the symbiotic functions of the fungus. For example, it has been shown that the proportion and speed of spore germination are higher in homokaryons, while the hyphal network structure is more complex in dikaryons (Serghi et al ., 2021).…”

“…Biotic stress is caused by other organisms such as insects, microbial pathogens, nematodes, and/or other plants (e.g. Bonaventure, 2018;Horvath et al, 2018;Marro et al, 2018;Shine et al, 2019). Meanwhile, the most studied abiotic stressors are drought, salinity, extreme temperatures, nutrient deficiency or heavy metals (Da Silva et al, 2011;Gupta et al, 2013;Parihar et al, 2015;Salehi-Lisar & Bakhshayeshan-Agdam, 2016;Mathur & Jajoo, 2020).…”

Arbuscular mycorrhizal fungal‐induced tolerance is determined by fungal identity and pathogen density

“…Although both Rhizophagus and Funneliformis are considered generalists (Öpik et al, 2006;Smith & Read, 2008), Funneliformis may be better suited for the crops preceding potato on this land (wheat, kale, leeks, kale and pea), hence its presence in the field. Additionally, host status is not as simple as previously thought as the strain of fungal species can impact its generalist nature (Serghi et al, 2021). This can be driven by the diversity of cropping, with polycultures promoting the largest diversity of AMF (Guzman et al, 2021) and possibly establishing a richer community for future crops.…”

Network traits predict ecological strategies in fungi

“…Early work measured fractal dimensions of mycelia at both micro- and macro-scales, and quantified their variation under different growth conditions or biotic interactions [ 15 , 16 ]. More recently, some researchers have systematically measured simple morphological traits (e.g., hyphal number and length, spore counting or branching frequency) and continuous growth parameters (e.g., hyphal extension rate and branching rates) using automated techniques to characterize trade-offs in hyphal morphology [ 17 ], life history [ 18 ], hyphal space-searching strategies [ 19 , 20 ] or to parametrize mathematical models of fungal colony growth [ 21 – 24 ].…”