Abstract
Morchella crassipes (Vent.) Pers., a typical yellow morel species with high economic value, is mainly distributed in the low altitude plains of Eurasia. However, rare research has been performed on its genomics and polarity, thus limiting its research and development. Here, we reported a fine physical map of the nuclear genome at the subchromosomal-scale and the complete mitochondrial genome of M. crassipes. The complete size of the nuclear genome was 56.7 Mb, and 23 scaffolds were assembled, with eight of them being complete chromosomes. A total of 11,565 encoding proteins were predicted. The divergence time analysis showed that M. crassipes representing yellow morels differentiated with black morels at ~33.98 Mya (million years), with 150 gene families contracted and expanded in M. crassipes versus the two black morels (M. snyderi and M. importuna). Furthermore, 409 CAZYme genes were annotated in M. crassipes, containing almost all plant cell wall degrading enzymes compared with the mycorrhizal fungi (truffles). Genomic annotation of mating type loci and amplification of the mating genes in the monospore population was conducted, the results indicated that M. crassipes is a heterothallic fungus. Additionally, a complete circular mitochondrial genome of M. crassipes was assembled, the size reached as large as 531,195 bp. It can be observed that the strikingly large size was the biggest up till now, coupled with 14 core conserved mitochondrial protein-coding genes, two rRNAs, 31 tRNAs, 51 introns, and 412 ncORFs. The total length of intron sequences accounted for 53.67% of the mitochondrial genome, with 19 introns having a length over 5 kb. Particularly, 221 of 412 ncORFs were distributed within 51 introns, and the total length of the ncORFs sequence accounted for 40.83% of the mitochondrial genome, and 297 ncORFs had expression activity in the mycelium stage, suggesting their potential functions in M. crassipes. Meanwhile, there was a high degree of repetition (51.31%) in the mitochondria of M. crassipes. Thus, the large number of introns, ncORFs and internal repeat sequences may contribute jointly to the largest fungal mitochondrial genome to date. The fine physical maps of nuclear genome and mitochondrial genome obtained in this study will open a new door for better understanding of the mysterious species of M. crassipes.
Highlights
True morels (Morchella spp.), an important edible mushroom distributed all over the world, especially in the North temperate zone, belong to Ascomycota phylum and Pezizomycetes class [1,2]
At both end of 8 scaffolds (LG1 to LG8), complementary telomere structures were identified with the repetitive unit of TTAGGGTTAG or CTAACCCTAA, implying that they might be complete chromosomes
The results showed that only one mating type gene fragment could be amplified from each ascospore, and two MAT gene fragments were obtained from the mycelium of tissue isolation (Figure 3d,e)
Summary
True morels (Morchella spp.), an important edible mushroom distributed all over the world, especially in the North temperate zone, belong to Ascomycota phylum and Pezizomycetes class [1,2]. Wild morels can produce ascocarps under suitable conditions in a short period of time from late spring to early summer, and their unique fragrance and taste attract a large number of hunters. In North America, many morel hunting activities were organized spontaneously in morel fruiting seasons, where participants enjoy the pleasure of hunting morels in nature, cooking and tasting them instantly [2,4]. The medicinal efficacy of morels was recorded in China about 600 years ago [1]. Modern medical research has shown that morel possesses various physiologically active properties, such as anti-oxidative, anti-inflammatory, anti-microbial, immunostimulatory, anti-tumor and so on [5,6,7]
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