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A genetic system controlling mitochondrial fusion in the slime mould, Physarum polycephalum
Abstract:
We have identified two distinct mitochondrial phenotypes, namely, Mif+ (mitochondrial fusion) and Mif- (mitochondrial fusion-deficient), and have studied the genetic system that controls mitochondrial fusion in the slime mould, Physarum polycephalum. A mitochondrial plasmid of approximately 16 kbp was identified in all Mif+ plasmodial strains. This plasmid is apparently responsible for promoting mitochondrial fusion, and it is inserted into the mitochondrial DNA (mtDNA) in successive sexual crossing with Mif- strains. This recombinant mtDNA and the unchanged free plasmid spread through the mitochondrial population via the promotion of mitochondrial fusion. The Mif+ strains with the plasmid were further classified as being two types: high frequency and low frequency mitochondrial fusion. Restriction analysis of the mtDNA suggested that the high frequency mitochondrial fusion type was more often heteroplasmic; within each plasmodium, mtDNAs of both parental types were usually present, in addition to the presence of the plasmid. Genetic analysis with the progeny obtained from crossing myxamoebae derived from three different isolates suggested that these progeny carried different alleles at a nuclear locus that controlled the frequency of mitochondrial fusion. These alleles (mitochondrial mating-type alleles, mitA1, 2 and 3) appear to function like the mating type of the myxamoebae; mitochondrial fusion occurs at high frequency with the combination of unlike alleles, but at low frequency with the combination of like alleles.
Insights
Researchers discovered a mitochondrial plasmid in Physarum polycephalum that drives mitochondrial fusion. This fusion process is genetically controlled by nuclear alleles, influencing the frequency of mitochondrial fusion.
Area of Science:
- Cell Biology
- Genetics
- Mycology
Background:
- Mitochondrial dynamics, including fusion and fission, are crucial for cellular function.
- The genetic control mechanisms underlying mitochondrial fusion are not fully understood in many organisms.
Purpose of the Study:
- To investigate the genetic basis of mitochondrial fusion in the slime mould, Physarum polycephalum.
- To identify factors responsible for distinct mitochondrial phenotypes (fusion-proficient and fusion-deficient).
Main Methods:
- Identification and characterization of mitochondrial plasmids.
- Restriction analysis of mitochondrial DNA (mtDNA).
- Genetic crosses using myxamoebae and analysis of progeny.
Main Results:
- A 16 kbp mitochondrial plasmid was identified in fusion-proficient (Mif+) strains, promoting mitochondrial fusion.
- The plasmid integrates into mtDNA during sexual crosses with fusion-deficient (Mif-) strains.
- Nuclear alleles (mitA1, 2, 3) control the frequency of mitochondrial fusion, with unlike alleles promoting high frequency and like alleles promoting low frequency.
Conclusions:
- A mitochondrial plasmid is a key factor in promoting mitochondrial fusion in Physarum polycephalum.
- Nuclear genetic factors (mitochondrial mating-type alleles) modulate the frequency of this fusion process.