Biochemical Genetic Analysis of Blue Light Responses in Neurospora Crassa
Paietta, John Vasinto
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https://hdl.handle.net/2142/71753
Description
Title
Biochemical Genetic Analysis of Blue Light Responses in Neurospora Crassa
Author(s)
Paietta, John Vasinto
Issue Date
1982
Department of Study
Genetics and Development
Discipline
Genetics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Genetics
Abstract
Physiological responses to blue light are widespread among prokaryotic and eukaryotic organisms. The photoreceptor for some of these responses, long a matter of controversy, may be a flavin or carotenoid. This dissertation applies a biochemical genetic approach to an analysis of the blue light responses in the fungus Neurospora. A major goal was to determine the nature of the Neurospora blue light photoreceptor. The key findings are as follows: (i) A correlation was found in riboflavin mutants between flavin deficiency and a reduced sensitivity to light. Flavin deficiency resulted in an 80-fold decrease in sensitivity for the photosuppression of circadian conidiation and reduced the photosensitivity for phase shifting and carotenogenesis to about 1/16th and 1/4th of normal, respectively. (ii) Riboflavin analogs were used to demonstrate that flavins can function as photoreceptors. The analogs 1-deazariboflavin and roseoflavin, which have red-shifted absorption, were effective photoreceptors for the photosuppression and phase shifting of circadian conidiation by 540 nm light, but were relatively ineffective for carotenogenesis. These results (i and ii) provide evidence for flavin photoreception in the blue light responses of Neurospora. (iii) The flavoprotein nitrate reductase was found not to be involved in the photoresponses being studied. The responses of photosuppression and phase shifting of circadian conidiation, as assayed in nitrate reductase mutants, showed no significant differences as compared to the responses in a strain which would utilize nitrate. The responses also occur on a medium which represses nitrate reductase activity. (iv) As a start towards the genetic dissection of the photoreception process, three mutants were isolated which did not exhibit photosuppression of circadian conidiation. The three lis ("light insensitive") mutations segregate as single nuclear genes, are nonallelic, and are recessive to wild type. The light insensitive phenotype of the mutants is restricted to the photosuppression response in that phase shifting and carotenogenesis are not altered. (v) A theoretical consideration of the role of photooxidiative processes in the evolution of circadian rhythmicity is also included.
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