Functional Analysis of a Novel ABL (Abnormal Browning Related to Light) Gene in Mycelial Brown Film Formation of Lentinula edodes.

Lentinula edodes is a globally important edible mushroom species that is appreciated for its medicinal properties as well as its nutritional value. During commercial cultivation, a mycelial brown film forms on the surface of the sawdust growth medium at the late vegetative stage. Mycelial film formation is a critical developmental process that contributes to the quantity and quality of the mushroom yield. However, little is known regarding the genetic underpinnings of brown film formation on the surface of mycelial tissue. A novel causal gene associated with the formation of the mycelial brown film, named ABL (Abnormal browning related to light), was identified in this study. The comparative genetic analysis by dihybrid crosses between normal and abnormal browning film cultivars demonstrated that a single dominant allele was responsible for the abnormal mycelium browning phenotype. Whole-genome sequencing analysis of hybrid isolates revealed five missense single-nucleotide polymorphisms (SNPs) in the ABL locus of individuals forming abnormal partial brown films. Additional whole-genome resequencing of a further 16 cultivars showed that three of the five missense SNPs were strongly associated with the abnormal browning phenotype. Overexpression of the dominant abl-D allele in a wild-type background conferred the abnormal mycelial browning phenotype upon transformants, with slender hyphae observed as a general defective mycelial growth phenotype. Our methodology will aid the future discovery of candidate genes associated with favorable traits in edible mushrooms. The discovery of a novel gene, ABL, associated with mycelial film formation will facilitate marker-associated breeding in L. edodes.

Development and Molecular Characterization of Novel Polymorphic Genomic DNA SSR Markers in Lentinula edodes.

Sixteen genomic DNA simple sequence repeat (SSR) markers of Lentinula edodes were developed from 205 SSR motifs present in 46.1-Mb long L. edodes genome sequences. The number of alleles ranged from 3-14 and the major allele frequency was distributed from 0.17-0.96. The values of observed and expected heterozygosity ranged from 0.00-0.76 and 0.07-0.90, respectively. The polymorphic information content value ranged from 0.07-0.89. A dendrogram, based on 16 SSR markers clustered by the paired hierarchical clustering' method, showed that 33 shiitake cultivars could be divided into three major groups and successfully identified. These SSR markers will contribute to the efficient breeding of this species by providing diversity in shiitake varieties. Furthermore, the genomic information covered by the markers can provide a valuable resource for genetic linkage map construction, molecular mapping, and marker-assisted selection in the shiitake mushroom.

Occurrence of dsRNA Mycovirus (LeV-FMRI0339) in the Edible Mushroom Lentinula edodes and Meiotic Stability of LeV-FMRI0339 among Monokaryotic Progeny.

dsRNA was found in malformed cultures of Lentinula edodes strain FMRI0339, one of the three most popular sawdust cultivated commercial strains of shiitake, and was also found in healthy-looking fruiting bodies and actively growing mycelia. Cloning of the partial genome of the dsRNA revealed the presence of the RdRp sequence of a novel L. edodes mycovirus (LeV), and sequence comparison of the cloned amplicon showed identical sequences sequence to known RNA-dependent RNA polymerase genes of LeV found in strain HKA. The meiotic stability of dsRNA was examined by measuring the ratio of the presence of dsRNA among sexual monokaryotic progeny. More than 40% of the monokaryotic progeny still contained the dsRNA, indicating the persistence of dsRNA during sexual reproduction. Comparing the mycelia growth of monokaryotic progeny suggested that there appeared to be a tendency toward a lower frequency of virus incidence in actively growing progeny.

Extracellular enzyme activities of the monokaryotic strains generated from basidiospores of shiitake mushroom.

To obtain basic information on the biochemical property of basidiospores of shiitake mushroom (Lentinula edodes), the ability of producing extracellular enzyme was assessed using a chromogenic plate-based assay. For the aim, amylase, avicelase, ß-glucosidase, CM-cellulase, pectinase, proteinase, and xylanase were tested against monokaryotic strains generated from forty basidiospores of two different parental dikaryotic strains of shiitake mushroom, Sanjo-101Ho and Sanjo-108Ho. These two parental strains showed different degree of extracellular enzyme activity. No identical patterns of the degree of enzyme activity were observed between monokaryotic strains and parental strains of the two shiitake cultivars. The degree of extracellular enzyme activity also varied among monokaryotic strains of the two shiitake cultivars. Our results showed that dikaryotic parental strains of shiitake mushroom produce monokaryotic basidiospores having very diverse biochemical properties.

Detection and recovery of hydrolytic enzymes from spent compost of four mushroom species.

To evaluate the potential of using the enzymes from spent mushroom compost (SMC) as an industrial enzyme, the production of alpha-amylase, cellulase, beta-glucosidase, laccase, and xylanase was determined from the SMC of four edible mushroom species (Pleurotus ostreatus, Lentinula edodes, Flammulina velutipes and Hericium erinaceum). Among the tested SMC, the SMC of L. edodes showed the highest enzyme activity in alpha-amylase (229 nkat/g), cellulase (759 nkat/g) and beta-glucosidase (767 nkat/g) in 0.5% Triton X-100, and that of P. ostreatus showed the highest activity in laccase (1452 nkat/g) in phosphate-buffered 0.2% Triton X-100. The highest xylanase activity (119 nkat/g) was found in the SMC of F. velutipes.

Comparative study of mycelial growth and basidiomata formation in seven different species of the edible mushroom genus Hericium.

The potential of using several agricultural by-products as supplements of sawdust substrate for the production of edible mushroom Hericium was evaluated using seven Hericium species. All the tested supplements (rice bran, wheat bran, barley bran, Chinese cabbage, egg shell, and soybean powder) were found to be suitable for the mycelial growth of all the tested species. In mycelial growth, soybean powder was the best supplement for Hericium americanum, Hericium coralloides, and Hericium erinaceum while barley bran was the best for Hericium alpestre, Hericium laciniatum, and Hericium erinaceus. For Hericium abietis, rice bran and Chinese cabbage was the best. The possibility of mushroom production on oak sawdust substrate with 20% rice bran supplement was demonstrated with H. coralloides, H. americanum, H. erinaceus, and H. erinaceum which showed 26-70% biological efficiency. Our results also showed that strain selection is important to improve biological efficiency and mushroom yield in Hericium cultivation.