D J Jacobson — Page 2 | PubMed Health

PubMed1994

A kalilo-like linear plasmid in Louisiana field isolates of the pseudohomothallic fungus Neurospora tetrasperma.

Two Louisiana strains of Neurospora tetrasperma contain a linear plasmid (LA-kalDNA) with a restriction map identical to the Hawaiian Neurospora intermedia senescence plasmid, kalDNA, but with termini 100 nucleotide pairs shorter. One of these strains also bore a circular plasmid similar to the Hawaiian circular plasmid Hanalei-2. One species probably acquired both plasmids from the other by horizontal transfer, at a time sufficiently distant for sequence divergence to take place. Many LA-kalDNA-bearing derivative strains senesced, but this plasmid does not guarantee senescence. Furthermore, LA-kalDNA does not insert into mtDNA. One senescent strain showed no LA-kalDNA. The plasmids are effectively transmitted via the pseudohomothallic sexual cycle. Single mating-type derivatives transmit plasmids maternally.

Biological Evolution↗

PubMed1992

Control of mating type heterokaryon incompatibility by the tol gene in Neurospora crassa and N. tetrasperma.

The mating-type of Neurospora crassa (A and a) have a dual function: A and a individuals are required for sexual reproduction, but only strains of the same mating type will form a stable vegetative heterokaryon. Neurospora tetrasperma, in contrast, is a naturally occurring A+a heterokaryon. It was shown previously that the mating-type genes of both species are functionally the same and are not responsible for this difference in heterokaryon incompatibility. This suggests that a separate genetic system determines the heterokaryon incompatibility function of mating type. The mutant tolerant (tol) in N. crassa, unlinked to mating type, acts as a specific suppressor of A+a heterokaryon incompatibility. In the present study, the wild-type alleles at the tol locus were introgressed reciprocally, from N. crassa into N. tetrasperma and from N. tetrasperma into N. crassa, to investigate the action of these alleles in the A+a heterokaryon incompatibility systems of these species. The wild-type allele from N. tetrasperma (tolT) acts as a recessive suppressor of A+a heterokaryon incompatibility in N. crassa. Furthermore, the wild-type allele from N. crassa (tolC) causes A and a to become heterokaryon incompatible in N. tetrasperma, while having no effect on the sexual reproduction. Therefore, the tol gene plays a major role in determining the heterokaryon compatibility of mating type in these species: tolC is an active allele that causes incompatibility and tolT an inactive allele that suppresses incompatibility by its inactivity.

Crosses, Genetic↗