Project description:Diverse sex determination mechanisms have been reported in eukaryotes, but little is known about the genetic pathways leading to sex determination in red algae. Sex-specific genes that could be involved in sex determination and sexual differentiation were investigated in a red alga Bostrychia moritziana by analyzing the transcriptomes of various phases including males, females and tetrasporophytes. Sex-dominantly-expressed genes which shows >10 fold difference between sexes were isolated using comparative RNA-seq analysis. We found 19 gene homologues, 10 from males and 9 from females, that were found only in one sex in genomic amplification. This suggests that these divergent homologues are on non-recombining, possibly different, chromosomes in their respective sexes. Most of the sex-specific genes are involved in important cellular processes including chromosome segregation, nucleo-cytoplasmic protein shuttling or tRNA modification. Quantitative PCR analysis also showed that some sex-specific genes were differently regulated during critical events of sexual reproduction like fertilization and carposporophyte development. We could also localize the expression of a male-specific gene in spermatia before and after gamete binding using RNA in situ hybridization. Another set of transcripts were found that were sex-dominantly-expressed, but not sex-specific. 19 out of 39 sex-dominantly-expressed transcripts were annotated to transposable elements, but none of them was sex-specific. Our results suggest that sexual differentiation in B. moritziana may be achieved by multi-level regulation of cellular processes, both from genes present only in one sex and differential expression of shared genes.
