A second HD mating type sublocus of Flammulina velutipes is at least di-allelic and active: new primers for identification of HD-a and HD-b subloci

Sexual development in is controlled by two different mating type loci (HD and PR). The HD locus contains homeodomain (Hd) genes on two separate HD subloci: HD-a and HD-b. While the functionality of the HD-b sublocus has been largely confirmed, the status and content of the HD-a sublocus has remained unclear. To examine the function of the HD-a sublocus, genome sequences of a series of strains were analyzed and tested through series of amplification by specific primer sets. Furthermore, activity of di-allelic HD-a locus was confirmed by crossing strains with different combinations of HD-a and HD-b subloci. Sublocus HD-b contained a large variety of fixed Hd1/Hd2 gene pairs, while the HD-a sublocus either contained a conserved Hd2 gene or, a newly discovered Hd1 gene that was also conserved. Identification of whole HD loci, that is, the contents of HD-a and HD-b subloci in a strain, revealed that strains with similar HD-b subloci could still form normal dikaryons if the two genes at the HD-a sublocus differed. At least di-allelic HD-a sublocus, is thus indicated to be actively involved in mating type compatibility. HD-a sublocus is active and di-allelic. Using the new information on the HD subloci, primers sets were developed that specifically amplify HD-a or HD-b subloci in the majority of strains. In this way, unknown HD mating types of can now be quickly identified, and HD mating type compatibility conferred by HD-a or HD-b can be confirmed by PCR.