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Heterkaryon Formation and Genetic Analyses of Color Mutants in Aspergillus heterothallicus

Kyung-Joo Kown and Kenneth B. Raper
American Journal of Botany
Vol. 54, No. 1 (Jan., 1967), pp. 49-60
Stable URL: http://www.jstor.org/stable/2440886
Page Count: 12
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Heterkaryon Formation and Genetic Analyses of Color Mutants in Aspergillus heterothallicus
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Abstract

Heterokaryon compatibility between strains of Aspergillus heterothallicus was tested by using prototrophic mutants of contrasting conidial head colors obtained by ultraviolet radiation. Heterokaryons were formed between mutants only when two conditions were fulfilled: The mutants had to be of the same mating type, and the isolates from which the mutants were derived had to be of similar macroscopic growth characteristics and mycelial pigmentation. Heterokaryotic heads were conspicuously striate, being composed of spore chains pigmented as the parental types, and representing, in most cases, examples of an "autonomous" nuclear action. Heterokaryotic heads of unusual interest, resulting from "autonomous-nonautonomous" type of gene actions, were produced in combinations of a pinkish tan (PT) mutant. The nuclear action of the PT mutant was nonautonomous regardless of the type of mutant with which it was paired, whereas the nuclear action of the other head-color mutants was autonomous. Genetic analyses of headcolor mutants were conducted by using all possible crosses between mutants derived from strains WB 4982 (A mating type) and WB 5086 (a mating type). It was found that similar color mutations of these two strains were allelic. All mutations responsible for different head colors, however, were found to be nonallelic to each other. The interactions between the different head-color mutants were studied in double mutants formed in the aforementioned crosses. Epistatic-hypostatic relationships between the different mutations were determined, and such relationships were used in the construction of a possible biosynthetic sequence leading to the production of the wild-type (green) pigment of conidial heads. The main sequential steps for the biosynthesis of conidial pigmentation appear to proceed from white to yellow, to brown, to brownish green, and to green.

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