Haploid vegetative mycelia of Armillaria gallica show among-cell-line variation for growth and phenotypic plasticity

Abstract

Vegetative mycelial cells of Armillaria are expected to have diploid nuclei. Cells from a single mycelium therefore would not be expected to differ from one another for ecologically relevant quantitative traits. We isolated two sets of basidiome cell lines (from spores and stipe cells) and one set of vegetative cell lines (from an attached rhizomorph) from a single contiguous Armillaria gallica mycelium. We isolated a second set of vegetative cell lines from the soil 20 cm from the above basidiome-rhizomorph complex. In all four sets of cell lines in situ DAPI-DNA measurements showed cells are haploid and quantitative-trait analyses of cell lines grown at different water potentials revealed high levels of among-cell-line genetic variation for both growth and phenotypic plasticity. Haploidy and the existence of ecologically relevant genetic variation within vegetative individuals are unexpected and mean that a process similar to evolutionary adaptation could take place within the soma of a genetic individual. We believe this is a key to understanding how large A. gallica mycelia survive exposure to variation in ecological conditions during lives that potentially span several tree (host) generations.

Phenotypic plasticity in fungi: a review with observations onAureobasidium pullulans

“…Experimental investigations of basic environmental signals, such as temperature, nutrients, pH, osmotic pressure, water potential, light and their interactions, also are possible (Wickerham and Kurtzman 1975;Hallsworth and Magan 1996;Peabody et al 2003Peabody et al , 2005Bago et al 2004). In addition complex signals, such as those that are involved in symbiotic associations, host immune mechanisms, virulence, pathogenesis and antigen-antibody interaction (i.e.…”

Genetic Diversity within an Italian Population of Forest Armillaria gallica Isolates as Assessed by RAPD‐PCR Analysis

“…Although there is evidence supporting genomic stability among individuals within the same population of A. gallica (Smith et al, 1992;Hodnett and Anderson, 2000), a recent discussion focused on adaptation strategies implemented by this species to face external changes over long periods of time and large areas. Somatic hyphae of A. gallica were lately found subject to a phenomenon known as genetic mosaicism, based on a frequent and regular genetic recombination owing to extrabasidial haploidizations, thus increasing variability and heterogeneity within individuals and, consequently, enabling the fungus to escape unfavourable environmental variations and stress conditions (Peabody et al, 2000(Peabody et al, , 2003(Peabody et al, , 2005. If these findings are exclusive for A. gallica, they could explain why the results of RAPD analysis here reported did not match the VC groups of isolates previously obtained from the same population of this species.…”

Mosaic fungal individuals have the potential to evolve within a single generation

“…Our earlier studies 7,8 are consistent with the existence of HGM in A. gallica; but analyses were limited to isozyme loci, mating-type loci, and a restriction fragment length polymorphism (RFLP) of IGS-1 in stipes. IGS-1 analyses were instructive but limited to one locus in one tissue type of a single individual 7,8 . In the present study RFLP analyses were expanded to include five loci in three tissue types from seven geographically distinct sites in southeastern Massachusetts, USA.…”

“…Raynham spore nuclei (N = 100), soil mycelium nuclei (N = 100), and rhizomorph hyphal filament nuclei (N = 100) were shown to be haploid in an earlier study of A. gallica growth responses to water potential 8 . To confirm haploidy of the current study's cultured rhizomorph hyphal filament lines, multiple nuclei were measured for nuclear DNA content in each of 10 lines in the Raynham and Bridgewater genets.…”

“…For comparison, cultured lines were compared to samples fixed in 95% ethanol within 2 h of collection from nature. These samples included 30 prophase I basidia nuclei, 30 spore nuclei, and 50 rhizomorph and soil mycelia (vegetative-stage) nuclei 8,17,18 (Supplementary Table S1). Because vegetative-stage nuclei and cultured rhizomorph nuclei were not normally distributed ( Fig.…”