Craig W. Banks, Sara Neville Bennett, and Wayne A. Krissinger- Department of Biology, Georgia Southern University, Statesboro, GA 30460 USA
The mutant overaccumulator of carotenoids, ovc, which we obtained from the Fungal Genetics Stock Center, had been reported by Harding, et al. (1984 Neurospora Newsl. 31:23-25) to be in the right arm of LG IV between col-4 and met-5. Examination of ovc in our laboratory revealed that in addition to having increased pigmentation, ovc was also osmotic sensitive and allelic to cut.
During a study of pigmentation mutants of Neurospora crassa, we obtained cultures of the mutant, overaccumulator of carotenoids, ovc (S20-16), from the Fungal Genetics Stock Center. Because our laboratory is also interested in osmotic-sensitive mutants which fail to grow on medium with elevated concentrations of NaCl, we make it a practice to test all strains we are working with for the osmotic-sensitive trait. When growth tested on Westergaard-Mitchell medium supplemented with 6% NaCl [W-M (6% NaCl)], ovc failed to grow, indicating that in addition to increased pigmentation, it was also osmotic sensitive.
The ovc locus was reported (Harding, et al. 1984 Neurospora Newsl. 31:23-25) to be in the right arm of LG IV between col-4 (about 10% recombination) and met-5 (about 14% recombination). Since the osmotic-sensitive mutant, os-2, is also in LG IVR near the reported locus of ovc, we next carried out a complementation test with ovc and os-2 on the salt-supplemented medium. The observation of growth indicated complementation and non-allelism of the two mutants.
Another osmotic-sensitive mutant, cut, is in LG IV, but in the left arm. In addition to being osmotic-sensitive, this mutant also exhibits increased pigmentation and an altered morphology with the aerial hyphae all ending at the same level in the culture tube, hence, the designation cut. Visually, cultures of ovc were found to be indistinguishable from those of cut. Complementation tests carried out between ovc and cut were negative, consistent with allelism of the two mutants.
Ascospores from a cross of ovc to cut were picked individually and the resulting 171 progeny were subcultured onto W-M (6% NaCl). None of the progeny grew on the salt medium and thus, no wild-type recombinants were recovered. Ascospores from the same cross were also mass plated directly onto W-M (6% NaCl) in order to allow the recovery of larger numbers of wild-type recombinants. No such recombinants were recovered from the approximately 24,712 ascospores plated. These results support allelism of ovc and cut. Since cut is in the left arm of LG IV, these mapping data differ from those of Harding, et al. (1984) which placed ovc in the right arm of LG IV. In light of these more recent data, we suggest that the map position of ovc be changed to the left arm of LG IV, allelic to the cut locus.
Return to the FGN 44 Table of Contents