Genetic determination of sporangiophore development in Phycomyces

Abstract

The mycelium of the fungus Phycomyces, essentially a giant multinucleate cell, produces two kinds of asexual reproductive structures, called macrophores and microphores, and a succession of structures for sexual reproduction. Following the treatment of spores with N-methyl-N'-nitro-N-nitrosoguanidine, conditional imb mutants have been isolated that form no macrophores at 2 6 T , but do at 14°C. At the restrictive temperature, few imb mutants (2 of 13) develop microphores, and none is able to complete the sexual cycle. This suggests that genes responsible for macrophorogenesis are involved in microphorogenesis and in sexual development as well. Light reduces macrophorogenesis and totally abolishes microphorogenesis in the wild type under the conditions of our experiments. These photomorphogenetic effects require the normal function of genes ma& and ma&, which are responsible for phototropism. Light inhibits microphorogenesis in the two imb mutants that form microphores at the restrictive temperature. Genetic alterations of carotenogenesis lead to an excess of microphores and a scarcity of macrophores in the dark, but they have little influence on vegetative reproduction in the light.

New Mutants of Phycomyces blakesleeanus for (beta)-Carotene Production

“…The original carF carS double mutant grew somewhat more slowly and produced fewer sporangiophores and spores than the wild type did. Strains with modifications in their ␤-carotene contents usually deviate from normal sporangiophore development (9,13). The failure of carS mutants to produce zygospores has previously been attributed to their high carotene contents.…”

Genes involved in carotene synthesis and mating in Blakeslea trispora

“…Those are probably related to the production of vegetative fruiting bodies (sporangiophores), which are formed only in single cultures and are repressed by mating, while zygospores are formed only in mated cultures. Most of the genes used by the related fungus Phycomyces for vegetative structures are used for sexual structures as well as indicated by the Wnding that all 13 mutants isolated for their inability to produce sporangiophores did not produce zygospores either (Gutiérrez-Corona and Cerdá-Olmedo 1988).…”