PCR-based markers for genetic mapping in Neurospora crassa.

Eighteen PCR-based markers are described for use in mapping mutations in Oak Ridge background strains of Neurospora crassa. These markers are located on each of the seven linkage groups and in the mitochondrial genome to enable course-scale linkage mapping. Following mapping to a linkage group, additional markers can be developed in the co-segregating region for fine-scale mapping of mutations. As with the N. crassa RFLP map (Metzenberg and Grotelueschen, 1993; Nelson and Perkins, 2000), the addition of PCR-based markers by members of the Neurospora community will enhance this marker set for mapping purposes. Creative Commons License This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License. This regular paper is available in Fungal Genetics Reports: http://newprairiepress.org/fgr/vol51/iss1/11 26 Fungal Genetics Newsletter PCR-based markers for genetic mapping in Neurospora crassa . Moshi Kotierk and Myron L. Smith, Carleton University, Ottawa-Carleton Institute of Biology, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada Fungal Genetics Newsletter 51:26-26 Eighteen PCR-based markers are described for use in mapping mutations in Oak Ridge background strains of Neurospora crassa . These markers are located on each of the seven linkage groups and in the mitochondrial genome to enable course-scale linkage mapping. Following mapping to a linkage group, additional markers can be developed in the co-segregating region for fine-scale mapping of mutations. As with the N. crassa RFLP map (Metzenberg and Grotelueschen, 1993; Nelson and Perkins, 2000), the addition of PCR-based markers by members of the Neurospora community will enhance this marker set for mapping purposes. Map-based or positional cloning is necessary to locate, identify and characterize genes that are associated with spontaneous or induced mutations. Methods available for locating mutations in Neurospora crassa involve co-segregation analysis using phenotypic (e.g. auxotrophic) markers. For example, multiply marked centromere tester strains of N. crassa are available for this purpose through the Fungal Genetics Stock Center (e.g. Perkins, 1972; Metzenberg et al., 1984). Often, however, co-segregation analysis with a set of phenotypic markers will not provide adequate resolution for the fine-scale linkage mapping necessary to clone a trait of interest and may require subsequent crosses to achieve further resolution. In this note, PCR-based markers are described for locating mutations generated in Oak Ridge background strains. The method takes advantage of abundant sequence differences between Oak Ridge and M auriceville genetic backgrounds, and the recently completed N. crassa genome sequence of the Oak Ridge standard strain 74-OR23-1VA (Galagan et al., 2003). The PCR-based markers are distributed throughout the seven N. crassa linkage groups and the mitochondrial DNA (Figure 1). Mapping of a mutation involves four steps. 1) Crossing an Oak Ridge-background mat-a strain bearing the mutation of interest with the Mauriceville-background strain, FGSC# 2225. 2) Locating the mutation to linkage group by identifying PCR-based polymorphism(s) that co-segregate with the mutation. 3) Generation of additional markers in the region of interest to carry out high-resolution mapping of the mutation. 4) Identification of the mutated gene by, for example, complementation with co-segregating open reading frames (ORFs) based on the N. crassa genome sequence. In Table 1, the primer sequences, location and PCR conditions are described for each of three types of polymorphisms identified . Amplified Product Length Polymorphisms (APLPs) are evident when PCR products are of different sizes. Also used is presence/absence of PCR product in the Oak Ridge and M auriceville strains, respectively. Finally, Restriction Fragment Length Polymorphisms (RFLPs) are used to identify internal sequence differences in PCR products that are the same size. Once the mutation is located to linkage group, mapping can be refined with additional markers in the co-segregating region using the N. crassa genome database as a reference to design primer pairs. We found the most efficient way to find PCR-based polymorphisms was to use primers placed within adjacent ORFs to obtain amplification products of non-coding, intergenic sequences. Polymorphisms in these non-coding regions are present in most cases between the Oak Ridge and M auriceville strains. As an example of the use of these markers, we examined their segregation with respect to a Supercontig 12 PCR-marker. Supercontig 12 was anchored to linkage group I and linkage group VI since it bore two and three markers from each linkage group, respectively. The segregation pattern for the Supercontig 12 marker indicates that it is located on linkage group I, between our met-6 and arg-13 markers. These 18 and other markers added by the Neurosporacommunity will provide a valuable resource for the positional cloning of traits of interest. Acknowledgments. Funding for this research was provided by a Discovery Grant to MLS from the Natural Sciences and Engineering Research Council of Canada and from the Mississaugas of the New Credit First Nation to M K. Dr. John Vierula kindly provided primers for the nmt-1 marker. Published by New Prairie Press, 2017