Abstract
Trioecy, a mating system in which males, females and hermaphrodites co-exist, is a useful system to investigate the origin and maintenance of alternative mating In the trioecious nematode Auanema rhodensis, males have one X chromosome (XO), whereas females and hermaphrodites have two (XX). The female versus hermaphrodite sex determination mechanisms have remained elusive. In this study, RNA-seq analyses show a 20% difference between the L2 hermaphrodite and female gene expression profiles. RNAi experiments targeting the DM (doublesex/mab-3) domain transcription factor dmd-10/11 suggest that the hermaphrodite sexual fate requires the upregulation of this gene. The genetic linkage map (GLM) shows that there is chromosome-wide heterozygosity for the X chromosome in F2 hermaphrodite-derived lines originated from crosses between two parental inbred strains. These results confirm the lack of recombination of the X chromosome in hermaphrodites, as previously reported. We also describe conserved chromosome elements (Nigon elements), which have been mostly maintained throughout the evolution of Rhabditina nematodes. The seven-chromosome karyotype of A. rhodensis, instead of the typical six found in other rhabditine species, derives from fusion/rearrangements events involving three Nigon elements. The A. rhodensis X chromosome is the smallest and most polymorphic with the least proportion of conserved genes. This may reflect its atypical mode of father-to-son transmission and its lack of recombination in hermaphrodites and males. In conclusion, this study provides a framework for studying the evolution of chromosomes in rhabditine nematodes, as well as possible mechanisms for the sex determination in a three-sexed species.
Original language | English |
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Pages (from-to) | 1211-1230 |
Number of pages | 20 |
Journal | G3: Genes | Genomes | Genetics |
Volume | 9 |
Issue number | 4 |
Early online date | 15 Feb 2019 |
DOIs | |
Publication status | Published - 9 Apr 2019 |
Keywords
- Auanema
- Genome
- Genetic map
- Nigon elements
- sex determination