Compatibility and incompatibility in hyphal anastomosis of arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal fungi (AMF), which live in symbiosis with 80 % of plants, are not able to grow when separated from their hosts. Spore germination is not host-regulated and germling growth is shortly arrested in the absence of host roots. Germling survival chances may be increased by hyphal fusions (anastomoses), which allow access to nutrients flowing in the extraradical mycelium (ERM). Perfect anastomoses, occurring with high frequency among germlings and the ERM of the same isolate, show protoplasm continuity and disappearance of hyphal walls. A low frequency of perfect fusions has been detected among co-specific genetically different isolates, although fungal nuclei have been consistently detected in all perfect fusions, suggesting active nuclear migration. When plants of different taxa establish symbioses with the same AMF species, anastomoses between ERM spreading from single root systems establish a common mycelium, which is an essential element to plant nutrition and communication. The interaction among mycelia produced by different isolates may also lead to pre-fusion incompatibility which hinders anastomosis formation, or to incompatibility after fusion, which separates the hyphal compartments. Results reported here, obtained by analyses of hyphal compatibility/ incompatibility in AMF, suggest that anastomosis formation and establishment of protoplasm flow, fundamental to the maintenance of mycelial physiological and genetic continuity, may affect the fitness of these ecologically important biotrophic fungi.

Dynamic Phosphate Uptake in Arbuscular Mycorrhizal Roots Under Field Conditions

“…Early studies suggested that the AMF genomic structure is highly heterogeneous; in other words, their coenocytic mycelia and spores contain a mixture of thousands of genetically different nuclei, so they might be heterokaryons (Sanders and Croll, 2010). This is supported by the observation that, in laboratory in vitro studies, anastomosis (hyphal fusion) can occur between genetically different AMF types, suggesting the potential for genetic variability of AMF (Chagnon, 2014;Novais et al, 2017). However, in the fungal genetic system, the somatic incompatibility system usually triggers programmed cell death because nonself hyphal fusion is a risky endeavor that can rapidly disrupt cellular homeostasis (Strom and Bushley, 2016).…”

Beneficial Services of Arbuscular Mycorrhizal Fungi – From Ecology to Application

“…In particular, new beneficial mycorrhizal traits can result from this kind of breeding scheme ( Angelard et al, 2010 ). However, anastomosis is only possible between compatible AM fungal isolates of the same, or perhaps closely related species ( de Novais et al, 2017 ), indicating that it requires genetic compatibility factors. Based on these findings, AM fungi could potentially be bred for improved symbiotic traits by systematic genetic reshuffling between divergent (but compatible) AM fungal isolates, followed by screening for the most beneficial new strains among AM fungal segregants.…”

In vitro Propagation of Arbuscular Mycorrhizal Fungi May Drive Fungal Evolution

“…Similar to other heterothallic fungal groups (Asco- and Basidiomycotan), nucleotype diversity may be maintained through anastomosis in wild populations of closely related AMF (Giovannetti et al, 1999, 2001, 2003; Croll et al, 2008). For AM fungi, anastomosis has been observed among hyphae of the same isolates during the asymbiotic and symbiotic stage even when growing in different systems but also been observed between closely related isolates (Giovannetti et al, 2001; Croll et al, 2009; Purin and Morton, 2011; De la Providencia et al, 2013; de Novais et al, 2013; Barreto De Novais et al, 2017). During anastomosis, plasmogamy can occur, and mitochondria (De la Providencia et al, 2013) and nuclei (Croll et al, 2008) can be shared between partners.…”