Chromosome-Wide Evolution and Sex Determination in the Three-Sexed Nematode Auanema rhodensis. Issue 4 (1st April 2019)

• Record Type: Journal Article
• Authors: Tandonnet, Sophie; Koutsovoulos, Georgios D; Adams, Sally; Cloarec, Delphine; Parihar, Manish; Blaxter, Mark L; Pires-daSilva, Andre
• Is Part Of: G3. Volume 9:Issue 4(2019)
• Page Start: 1211
• Page End: 1230
• Publication Date: 2019-04-01
• Subjects: Auanema -- genome -- genetic map -- Nigon elements -- sex determination -- Genetics of Sex; Genetics -- Research -- Periodicals; Genomics -- Periodicals; Genetics; Genomics; Genes; Genetics -- Research; Genomics; Electronic journals; Periodical; Periodicals; Fulltext; Internet Resources; Periodicals; 572.8
• DOI: 10.1534/g3.119.0011
• Languages: English
• ISSNs: 2160-1836

Abstract

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 strategies. In the trioecious nematode Auanema rhodensis, males have one X chromosome (XO), whereas females and hermaphrodites have two (XX). The female vs. 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.