| Description |
The dikaryotic phase dominates most of the life cycle in basidiomycetes, and each cell carries two different haploid nuclei. Interactions between these two nuclei have long been of interest but remain mostly unknown. Our study applied a nucleus-by-nucleus strategy to generate a complete, high-quality asymmetric dikaryotic genome of Tremella fuciformis Tr01, in which we identified several inter-nuclear chromosomal arrangements that resulted in chromosome number, size, and content difference between the two nuclei. Each nucleus has a two-speed genome, harboring three accessory chromosomes and two accessory compartments that can effect horizontal chromatin transfer between nuclei. Few basidiospores are ejected from fruiting bodies of Tr01. Most of the monospore isolates sequenced belong to Haplotype A genome architecture, and their genome sequences are biased towards those of the Haplotype A nucleus. More than one-third of monospore isolates carry one or two extra chromosomes including Chr12B and two new chromosomes ChrN1 and ChrN2. We hypothesize that the homologous regions of seven sister chromatids pair into a large complex during meiosis, which is followed by inter-chromosome recombination at physical contact sites and formation of new chromosomes. Irregular migration during meiosis of centromere-free chromosomes such as Chr12B, ChrN1, and ChrN2 results in aneuploidy of some daughter cells and infertility of most other daughter cells. Our results allow us to propose a model for the possible meiotic behaviors of an asymmetric dikaryotic genome in basidiomycete fungi and a new approach for sporeless mushroom breeding. |
