Allele-Specific Expression Reveals the Importance of Heterokaryon in Flammulina filiformis Life History
Yuan-Yuan Liu1, Lu-Yu Xie2, Chuan-Zheng Wei1, and Bao-Gui Xie1*
1 Mycological Research Center, College of Life Sciences, Fujian Agriculture and Forestry University
2 School of Computing, National University of Singapore
In most mushroom fungi, heterokaryon mycelia can develop into normal fruiting bodies, which is often called hybrid vigor. However, the biological significance of the expression of different nuclear genes for the process of fruiting body formation and development has not been revealed. Flammulina filiformis, a typical heterokaryon fungus, was taken as the model species in this study. We sequenced the genomes of two compatibility monokaryon strains, and obtained 12879 alleles that could be used for analysis of specific expression. Transcriptome sequencing was performed on different growth and development stages and different tissue materials of heterokaryon strains obtained by mating two monokaryon strains, and the expression levels of each SNP in alleles in the two parents were analyzed. It was found that alleles expressed in two nuclei of heterokaryon could be divided into three types: single gene expression (gene expression in only one nucleus), unbalanced expression (high expression in one nucleus, low expression in the other nucleus), and balanced expression (equal expression in two nuclei). It was found that the expression of alleles in basic metabolic pathways (ribosome, mRNA surveillance pathway, glycolysis/gluconeogenesis, etc.) of the life activities of Flammulina filiformis was generally balanced expression. It was also found that alleles with specific expression (single gene expression, unbalanced expression) were different in different growth and development stages and different tissues. These results indicated that alleles on the two nuclei of heterokaryons may involve in the regulation of mycelium growth and fruity body growth and development through specific expression, which provided a new way for to study basic biological questions of why the heterokaryon of Flammulina filiformis can grow and develop normally.