Abstract
Phycomyces blakesleeanus is a member of the subphylum Mucoromycotina. A genetic map was constructed from 121 progeny of a cross between two wild type isolates of P. blakesleeanus with 134 markers. The markers were mostly PCR-RFLPs. Markers were located on 46 scaffolds of the genome sequence, covering more than 97% of the genome. Analysis of the alleles in the progeny revealed nine or 12 linkage groups, depending on the log of the odds (LOD) score, across 1583.4 cM at LOD 5. The linkage groups were overlaid on previous mapping data from crosses between mutants, aided by new identification of the mutations in primary metabolism mutant strains. The molecular marker map, the phenotype map and the genome sequence are overall congruent, with some exceptions. The new genetic map provides a genome-wide estimate for recombination, with the average of 33.2 kb per cM. This frequency is one piece of evidence for meiosis during zygospore development in Mucoromycotina species. At the same time as meiosis, transmission of non-recombinant chromosomes is also evident in the mating process in Phycomyces. The new map provides scaffold ordering for the genome sequence and a platform upon which to identify the genes in mutants that are affected in traits of interest, such as carotene biosynthesis, phototropism or gravitropism, using positional cloning.
Highlights
The fungus Phycomyces blakesleeanus is a member of the order Mucorales in the subphylum Mucoromycotina
The primary goal of this project was to develop a genetic map covering the genome that could be used for map-based cloning to identify these unknown genes
For the analysis of mutant auxotrophic phenotypes, these were scored by the presence or absence of growth on yeast nitrogen base (YNB) medium
Summary
The fungus Phycomyces blakesleeanus is a member of the order Mucorales in the subphylum Mucoromycotina. The early branches in the fungal kingdom receive relatively little research attention, despite our potential ability to understand the evolution of the fungi through their study. This paucity in research effort is surprising in the context of the long research history associated with some Mucoromycotina species, especially on the mating properties of fungi. The genes required for mating in the Mucorales are poorly understood, and completing the sexual cycle under laboratory conditions is often a challenge In addition to these obstactles, many species are difficult to manipulate via the introduction of foreign DNA. The current absence of a stable transformation system in Phycomyces prevents the use of techniques such as cloning by complementation or gene function testing via disruption or RNAibased silencing [10]
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