Plasmodial incompatibility in the myxomycetes: a review

Two myxomycete phaneroplasmodia of the same species undergo somatic fusion only if they are phenotypically identical for a complex genetic incompatibility system. This system consists of a three tiered polygenic complex with dominant and recessive alleles. Thus, plasmodia must be phenotypically identical for approximately 16 loci in order to fuse (CC and Cc are phenotypically identical, but different from cc). The first level of the system (having a minimum of seven Fus loci) controls membrane fusion, and it apparently prevents fusion unless the two plasmodia have identical membrane or slime sheath components. The second level (having a minimum of six Cz loci) produces a rapid lysis of a small mixed region, of the two plasmodia, if membrane fusion has occurred. This lysis is directional in that it targets the recessive phenotype, and it is apparently triggered by some pre-formed substances when they come into contact with a different plasmodium. The third level (having a minimum of three Let loci) comes into play if membrane fusion occurs and there is no rapid lysis of the mixed plasmodium. It produces a slow lethal reaction, which targets and degrades the nuclei of the recessive phenotype. This reaction occurs over a period of five to twenty hours and requires the synthesis of new RNA and proteins. Since, this complex system produces a minimum of 65,536 different incompatibility phenotypes, it is highly unlikely that any two phaneroplasmodia will undergo a successful fusion unless they are very closely related. Species with aphaneroplasmoida apparently have a similar system, but species with small protoplasmodia do not appear to undergo any type of plasmodial fusion

18S rDNA Phylogeny of Lamproderma and Allied Genera (Stemonitales, Myxomycetes, Amoebozoa)

The phylogenetic position of the slime-mould genus Lamproderma (Myxomycetes, Amoebozoa) challenges traditional taxonomy: although it displays the typical characters of the order Stemonitales, it appears to be sister to Physarales. This study provides a small subunit (18S or SSU) ribosomal RNA gene-based phylogeny of Lamproderma and its allies, with new sequences from 49 specimens in 12 genera. We found that the order Stemonitales and Lamproderma were both ancestral to Physarales and that Lamproderma constitutes several clades intermingled with species of Diacheopsis, Colloderma and Elaeomyxa. We suggest that these genera may have evolved from Lamproderma by multiple losses of fruiting body stalks and that many taxonomic revisions are needed. We found such high genetic diversity within three Lamproderma species that they probably consist of clusters of sibling species. We discuss the contrasts between genetic and morphological divergence and implications for the morphospecies concept, highlighting the phylogenetically most reliable morphological characters and pointing to others that have been overestimated. In addition, we showed that the first part (∼600 bases) of the SSU rDNA gene is a valuable tool for phylogeny in Myxomycetes, since it displayed sufficient variability to distinguish closely related taxa and never failed to cluster together specimens considered of the same species

Plasmodial incompatibility in the myxomycetes: a review

Clark J, Haskins EF 2012 -Plasmodial incompatibility in the myxomycetes: a review. Mycosphere 3(2), 131-141, Doi 10.5943/mycosphere/3/2/3 Two myxomycete phaneroplasmodia of the same species undergo somatic fusion only if they are phenotypically identical for a complex genetic incompatibility system. This system consists of a three tiered polygenic complex with dominant and recessive alleles. Thus, plasmodia must be phenotypically identical for approximately 16 loci in order to fuse (CC and Cc are phenotypically identical, but different from cc). The first level of the system (having a minimum of seven Fus loci) controls membrane fusion, and it apparently prevents fusion unless the two plasmodia have identical membrane or slime sheath components. The second level (having a minimum of six Cz loci) produces a rapid lysis of a small mixed region, of the two plasmodia, if membrane fusion has occurred. This lysis is directional in that it targets the recessive phenotype, and it is apparently triggered by some pre-formed substances when they come into contact with a different plasmodium. The third level (having a minimum of three Let loci) comes into play if membrane fusion occurs and there is no rapid lysis of the mixed plasmodium. It produces a slow lethal reaction, which targets and degrades the nuclei of the recessive phenotype. This reaction occurs over a period of five to twenty hours and requires the synthesis of new RNA and proteins. Since, this complex system produces a minimum of 65,536 different incompatibility phenotypes, it is highly unlikely that any two phaneroplasmodia will undergo a successful fusion unless they are very closely related. Species with aphaneroplasmoida apparently have a similar system, but species with small protoplasmodia do not appear to undergo any type of plasmodial fusion