Cytology of Non-self Hyphal Fusions and Somatic Incompatibility in Phanerochaete velutina

Abstract

The somatic incompatibility reaction occurring at sites of fusion between hyphae of genetically different secondary mycelia of Phanerochaete velutina has been examined using combined light and electron microscopy. Hyphal compartments affected by incompatibility rapidly showed increased vacuolation and the development of autophagic bodies throughout the cytoplasm. Dense osmiophilic spherical bodies that developed within the vacuole lumen characterized the early and highly regulated phase of the reaction. Eventually, as expansion of the vacuolar system proceeded, more widespread degeneration began in the remaining cytoplasm, nuclei and mitochondria. The large microtubule bundles present within this species showed variable behaviour during degeneration of the cell compartments, either breaking down early on in the process or persisting intact during breakdown of the other cell components. The incompatibility finally caused extensive disruption and death of the compartments engaged in fusion and often contiguous cells. Plugging of dolipore septa apparently restricted spread of the incompatibility response along the fused hyphae. 0001-2925 0 1986 SGM

Cytological analysis of mycelial incompatibility in Rosellinia necatrix

“…Although the cytological studies for heterogenic incompatibility were reported in numerous articles, there were a few reports concerning about the time course of the death (Aylmore & Todd 1986;Newhouse & MacDonald 1991;Jacobson et al 1998). Our ultrastructural study revealed that collapse of cellular components began with the tonoplast and subsequently continued with the plasma and nuclear membranes.…”

“…In the incompatibility reaction of P. anserina, autophagy-related genes were up-regulated, suggesting that PCD as a result of incompatibility in P. anserina is autophagic type II PCD (Pinan-Lucarr e et al 2003). Although the increased vacuolization was reported in various heterogenic incompatibility systems (Ainsworth & Rayner 1986;Aylmore & Todd 1986;Saupe 2000;Glass & Kaneko 2003), it was not clear whether the increased vacuolization was correlated with tonoplast collapse because the vacuolation was not prominent in R. necatrix.…”

Programmed Cell Death and Apoptosis in Fungi

“…Many fungi undergo a vegetative or heterokaryon incompatibility response (Leslie and Zeller 1996;Glass et al 2000) which has been likened to apoptosis in animals (Aylmore and Todd 1986;Ainsworth et al 1990;Jacobson et al 1998;Ramsdale 1998). PCD in this situation is linked to the recognition of non-self (indicated by allelic differences at so-called vegetative or heterokaryon incompatibility loci), which may operate to prevent non-self takeover reactions (Rayner 1991) or to prevent the spread of harmful genetic elements such as viruses (Hartl et al 1975;Anagnostakis and Day 1979;Debets et al 1994;van Diepeningen et al 1997).…”

“…Somatic incompat-ibility is often associated with the generation of ROS (possibly through the action of phenoloxidase enzyme systems such as laccase) and an increase in proteolytic activity (Esser and Blaich 1994). EM studies of rejection responses reveal nuclear degradation (which is often restricted to one partner in an interaction; Aylmore and Todd 1986) and the accumulation of vesicular bodies. Marek et al (2003) examined the cytology of the heterokaryon incompatibility responses and senescence in Neurospora crassa and were able to demonstrate TUNEL-positive nuclei in transformants containing incompatible het-c alleles.…”

Living apart together: modelling the consequences of the dikaryotic life cycle of mushroom-forming fungi for genomic conflict

“…Di-mon mating, clearly impossible for a diploid organism, has been thought to be the main benefit of the dikaryotic lifestyle (Raper, 1966 p.264). The exchange of nuclei between dikaryons is thought to be prevented in nature since fusion of two dikaryons triggers nonself recognition followed by apoptosis, quickly killing the fused cell (Auxier et al, 2021;Aylmore & Todd, 1986). The prolonged mating opportunities of the dikaryon allow a nuclear genotype increased access to resources, as it retains its share of resources in the original dikaryon, and gains access to additional resources of the newly fertilized dikaryon.…”