Characterization of mating-type idiomorphs suggests that Morchella importuna, Mel-20 and M-sextelata are heterothallic

Morels (Morchella spp.) are highly prized for their culinary qualities and intensively collected worldwide by my-cophiles. Morels are divided into three clades by phylogenetic analyses: black morels, yellow morels and the rufobrunnea clade. Morchella importuna, Mel-20 and M. sextelata are included in the black morel clade and are widely distributed in Yunnan province, China. M. importuna and M. sextelata have been artificially cultured in recent years, but their life cycles and reproductive systems are still poorly understood, which delays the progress of morel cultivation. In this study, the genomes of two ascospore isolates of M. importuna with opposite mating-type were sequenced and two idiomorphs, MAT1-1 and MAT1-2, were identified. The MAT1-2 idiomorph was 6.7 kb in length containing a single MAT1-2-1 gene, and the MAT1-1 idiomorph was 10.5 kb containing a MAT1-1-1 gene and two other open reading frames (ORFs), GME3123 and GME3124. These ORFs differed greatly from the homologues of previously published mating-type genes; therefore, we speculate that they are novel mating genes found only in morels. Single-ascospore populations of M. importuna, M. sextelata and Mel-20 were analysed, and the result indicated that the ratios of MAT1-1- and MAT1-2-harbouring idiomorphs were not significantly different from a 1: 1 ratio. The results suggest that these three black morels are heterothallic.