Heterokaryosis and diploid formation among Brazilian isolates of Macrophomina phaseolina

Abstract

Heterokaryosis is the association of genetically distinct nuclei in a common hyphal cytoplasm, and is a process involved in the generation of fungal variation. The fusion of the distinct nuclei within a heterokaryotic hypha produces a heterozygous diploid nucleus and is one of the stages of the parasexual cycle. A heterokaryon's viability depends on the isolates’ genetic constitution with regard to loci called het (heterokaryon incompatibility) or vic (vegetative incompatibility). The current study evaluates for the first time the diversity of vegetative compatibility reactions in isolates of Macrophomina phaseolina from different hosts. Complementary nit (nitrate non‐utilizing) mutants of each isolate were obtained and paired in all possible combinations. Isolates were classified in vegetative compatibility groups (VCG) according to their ability to form viable heterokaryons. Ten VCGs were identified, two of them containing two isolates, and the remainder containing a single isolate. When grown on basal medium, heterokaryons produced both (i) auxotrophic segregants exhibiting the same phenotype as the paired mutants; and (ii) a fast‐growing sector, characterized as a heterozygous diploid sector, named D653, which showed a nit+ phenotype with a growth rate similar to the original wild isolate. When grown in the presence of benomyl, a haploidizing agent, D653 produced auxotrophic haploid segregants exhibiting the nit phenotypes of the crossed mutants. The results demonstrate for the first time the ability of M. phaseolina isolates to form viable heterokaryons and heterozygous diploid nuclei, suggesting that the parasexual cycle may be an alternative source of genetic variability in this species.

Population genomic analysis reveals geographic structure and climatic diversification for Macrophomina phaseolina isolated from soybean and dry bean across the United States, Puerto Rico, and Colombia

“…These models have been used to describe the population structure of plant pathogens with mixed modes of reproduction or inferred recombination ( Grünwald and Hoheisel, 2006 ; Milgroom et al, 2014 ; 2016 ; Milgroom, 2015 ). While little is known about the occurrence of recombination in M. phaseolina , recent studies have started to shed light on potential recombination mechanisms involving parasexuality ( Pereira et al, 2018 ) and horizontal gene transfer mediated by giant mobile genetic elements ( Gluck-Thaler et al, 2022 ). Whether other potential recombination mechanisms occur, and the frequency of recombination in M. phaseolina remains an important and exciting area of study.…”

Limitation of nitrogen source facilitated the production of nonmeiotic recombinants in Aspergillus nidulans

“…Heterokaryons and nonmeiotic recombinants were inoculated in different culture media: (a) sodium nitrate‐low medium (basal medium, BM): 1,000 ml distilled H 2 O; 10 g sucrose; 2 g NaNO 3 ; 1 g KH 2 PO 4 ; 0.5 g MgSO 4 ·7 H 2 O; 0.5 g KCl; 10 mg FeSO 4 ·7 H 2 O; 15 g agar; 0.2 ml trace element solution (95 ml distilled H 2 O; 5 g citric acid; 1 g Fe(NH 4 ) 2 (SO 4 ) 2 ·6 H 2 O; 0.25 g CuSO 4 ·5 H 2 O; 50 mg MnSO 4 ·H 2 O; 50 mg H 3 BO 3 ; and 50 mg Na 2 MoO 4 ·2 H 2 O); (b) sodium nitrate‐rich medium (minimal medium, MM): 1,000 ml distilled H 2 O; 10 g glucose, 6 g NaNO 3 ; 0,52 g KCl; 1.52 g KH 2 PO 4 ; 0.52 g MgSO 4· 7 H 2 O; 2 mg FeSO 4· 7 H 2 O; 1 mg ZnSO 4 ·7H 2 O; 1 mg CuSO 4 ·5 H 2 O; 15 g agar; (c) selective medium (SM) consisting of MM supplemented with nutritional requirements of the crossing strains with the omission of one of them, in each type of medium; (d) complete medium (CM) . A. nidulans 's master strains used to form heterokaryons and the nonmeiotic recombinants obtained from such heterokaryons are described in Table S1.…”

“…Furthermore, errors may occur during mitotic divisions of the diploid nucleus, causing sequential losses of chromosomes previously present in the two copies, and resulting in the production of recombinant haploid nuclei. The sequence of events that yield such recombinant nuclei constitutes the parasexual cycle that provides an effective pathway to increase genetic variability in fungi, especially those with no sexual cycle .…”

“…Heterokaryons and nonmeiotic recombinants were inoculated in different culture media: (a) sodium nitratelow medium (basal medium, BM): 1,000 ml distilled H 2 O; 10 g sucrose; 2 g NaNO 3 ; 1 g KH 2 [7]. A. nidulans's master strains used to form heterokaryons and the nonmeiotic recombinants obtained from such heterokaryons are described in Table S1.…”