Term of Award

Summer 1988

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Sara Neville Bennett

Committee Member 1

Wayne A. Krissinger

Committee Member 2

Donald J. Drapalik

Abstract

Back crosses to wild type N. crassa 74a were made with two morphological mutants previously isolated in the Neurospora Laboratory at GSC. These mutants were SS-302-14 and M134-19-17.

The mutant SS-302 possessed altered morphology displayed by the typical osmotic—sensitive mutants and was osmotic sensitive. Analysis of crosses of SS-302 to wild type showed that altered morphology and osmotic sensitivity co-segregated with no recombinant progeny produced. These results suggest pleiotrophic control of the traits of altered morphology and osmotic sensitivity. Further analysis indicated that SS-302 morphology was linked to the mating type locus with approximately 12% recombination between these loci. Allelism of SS-302 to sor(T9) was excluded on the basis of wild type recombinant progeny produced in crosses between these two mutants. Tests for allelism to os-4 were inconclusive due to the fact that repeated attempts to cross these mutants were unsuccessful and with complementation test, heterokaryon formation could not be confirmed due to absence of forcing markers. Microscopic observation revealed the absence of normal appearing protoperithecia suggesting female sterility in the mutant SS-302. Mapping data indicated that the locus for SS-302 lies approximately 25 map units to the right of lys-4 in the right arm of LGI.

The second mutant investigated in this study, M134-19-17, possessed altered morphology and was osmotic sensitive. Altered morphology in this case consisted of densely packed clusters of conidia uniformly spread across a reduced mycelium. Scanning electron microscopy revealed that the morphology of conidiophores and the extent of conidiation differed between M134 and wild type. After forty eight hours of incubation, cultures of wild type displayed well developed conidiophores with moderately developed proconidial chains. Cultures of M134 of the same age had extensive conidiophores with elaborate primary, secondary and tertiary branches differing in arrangement and appearance from those of wild type and often forming flask shaped clusters of conidia. After six days the mutant displayed densely packed clusters of conidia uniformly spread across a reduced mycelial mat. Light microscopy was used to compare the asexual life cycle of the mutant and the wild type. Results indicate that the mutant displayed delayed germination and premature conidiation when compared to the wild type strain. The process of conidiation in the mutant occurred on a highly reduced mycelial mat while an extensive mycelium had formed before conidiation was initiated in the wild type strain.

In crosses of M134 to wild type, altered morphology and osmotic sensitivity segregated with recombinant progeny produced. When these recombinant progeny were back crossed to wild type to confirm their recombinant nature, progeny were produced displaying traits not present in either parent. These results suggest modifier systems present in the M134 mutant. Analysis of mapping data with M134 indicated that the locus for this mutant lies approximately nine map units to the right of the lys-4 locus in the right arm of LGI.

Copyright

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