Hostname: page-component-7b7567c8c-jswmv Total loading time: 0 Render date: 2026-11-15T16:10:53.551Z Has data issue: false hasContentIssue false

Induced mitotic crossing-over in Ustilago maydis

Published online by Cambridge University Press:  14 April 2009

Robin Holliday
Affiliation:
John Innes Institute, Bayfordbury, Hertford, Herts.
Rights & Permissions [Opens in a new window]

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the 'Save PDF' action button.

1. Two different methods of selection were used to obtain stable prototrophic solopathogenic strains of Ustilago maydis from haploids with different biochemical requirements. The strains were shown to be heterozygous diploids.

2. Two diploids which were examined in detail had four markers in common, but they were in different coupling and repulsion phases. Rare spontaneous segregation was detected in one of the diploids, but a high frequency of segregation was obtained in both after treatment with ultra-violet light. The proportion of segregants amongst the survivors increased with the dose. These auxotrophic segregants were detected by means of the replica plating technique.

3. The types of segregant which were obtained from both diploids were consistent with the view that they arose as a result of mitotic crossing-over. After low doses of radiation the reciprocal products of crossing-over were often detected. There was no evidence from the phenotypes of the segregants that haploidization was occurring. The diploidy of a sample of the segregants was confirmed by mating-type tests, and by the fact that they showed further segregation after another dose of radiation.

4. A slow-growing unstable segregant recovered after a high dose of radiation proved to be a monosomic strain which consistently reverted to a stable diploid homozygous for one chromosome. It was possible to use this auxotrophic diploid together with a haploid with different biochemical requirements, to synthesize a prototrophic triploid strain. The triploid was much less stable than the diploid strains.

5. By means of pathogenicity tests with certain segregants it was possible to distinguish the function of the two loci which control the mating system. The a locus is responsible for the fusion of haploid sporidia and has no effect on the pathogenicity of the heterokaryon which is under the control of the b locus.

6. The effects of ultra-violet light on mitotic crossing-over do not seem to be easily compatible with a copy choice or similar mechanism of recombination.

Information

Type
Research Article
Copyright
Copyright © Cambridge University Press 1961