Genome and Transcriptome analysis for Closterium peracerosum-strigosum-littorale complex
In this study, we identified more than two-fold heritable genome size variation among unicellular Zygnematophycean algae, Closterium peracerosum-strigosum-littorale (C. psl.) complex, based on short-read sequencing analysis of 21 natural strains and F1 segregation analysis. Six de novo assembled genomes revealed that genome size variation is largely attributable to genome-wide copy number variation (CNV) between strains rather than mating-type-linked genomic regions or specific repeat sequences such as rDNA. Notably, 30% of genes showed CNV even between strains that can mate with each other. Transcriptome and gene ontology analysis demonstrated that CNV distributes nonrandomly in terms of gene functions, such that CNV were more often observed in the gene set with stage-specific expression. Furthermore, the expression level does not increase proportionately as the gene copy number increases in about 30% of these CNV genes, suggesting a mechanism of dosage compensation, which were over-represented in genes involved in basic biological functions, such as translation. Nonrandom patterns in gene duplications and corresponding expression changes in terms of gene functions may contribute to the maintenance of high level of CNV in association with extensive genome size variation in the C. psl. complex, despite its possible detrimental effects.