Morphological characterization of sex-deficient mutants of the homothallic zygomycete Zygorhynchus moelleri

• The mutants are arrested in different stages of the sexual development.
• Two mutants accumulate carotene over time (UV139 and UV542).
• The mutants show a light dependent asexual sporulation.
• Methionine plays a role in development of Zygorhynchus moelleri.

Heterothallic zygomycetes consist of two mating types, named plus and minus, whereas in homothallic species the genetic information for both mating types is present in one individual and nucleus. Nevertheless, zygophores, specialized sexual hyphae, of homothallic species harbor a plus or minus identity in the sexual reaction. Because of the lack of knowledge about the molecular and genetic background of the sexual development in zygomycetes, we used UV mutagenesis to create sexual defective mutants of Zygorhynchus moelleri. Our aim was to provide a set of mutants, which are helpful to identify new genes involved in the sexual morphogenesis. The six mutants presented here are arrested in different stages of the sexual development. Two mutants UV139 and UV542 predominantly produce only zygophores, whereas in two other mutants UV44 and UV48 the formation of gametangial walls is inhibited. Mutant UV554 seems to be blocked in the zygospore formation, whereas in mutant UV112 the wall formation of the zygosporangium is inhibited. We additionally isolated one methionine auxotroph, mutant UV127, which is blocked in the sexual and asexual development at low methionine concentrations, revealing the importance of methionine in the developmental processes of Z. moelleri.