Genetic mapping and transcription analyses of resistance gene loci in potato using NBS profiling.

NBS profiling is a method for the identification of resistance gene analog (RGA) derived fragments. Here we report the use of NBS profiling for the genome wide mapping of RGA loci in potato. NBS profiling analyses on a minimal set of F1 genotypes of the diploid mapping population previously used to generate the ultra dense (UHD) genetic map of potato, allowed us to efficiently map polymorphic RGA fragments relative to 10,000 existing AFLP markers. In total, 34 RGA loci were mapped, of which only 13 contained RGA sequences homologous to RGAs genetically positioned at approximately similar positions in potato or tomato. The remaining RGA loci mapped either at approximate chromosomal regions previously shown to contain RGAs in potato or tomato without sharing homology to these RGAs, or mapped at positions not yet identified as RGA-containing regions. In addition to markers representing RGAs with unknown functions, segregating markers were detected that were closely linked to four functional R genes that segregate in the UHD mapping population. To explore the potential of NBS profiling in RGA transcription analyses, RNA isolated from different tissues was used as template for NBS profiling. Of all the fragments amplified approximately 15% showed putative intensity or absent/present differences between different tissues suggesting putative tissue specific RGA or R gene transcription. Putative absent/present differences between individuals were also found. In addition to being a powerful tool for generating candidate gene markers linked to R gene loci, NBS profiling, when applied to cDNA, can be instrumental in identifying those members of an R gene cluster that are transcribed, and thus putatively functional.