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PLoS Genet. 2017 Jun 8;13(6):e1006777. doi: 10.1371/journal.pgen.1006777. eCollection 2017 Jun.

Hybridization and polyploidy enable genomic plasticity without sex in the most devastating plant-parasitic nematodes.

Author information

1
INRA, Université Côte d'Azur, CNRS, ISA, France.
2
Bioinformatics Center, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, Japan.
3
Commissariat à l'Energie Atomique (CEA), Institut de Génomique (IG), Genoscope, Evry, France.
4
LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, France.
5
Université Libre de Bruxelles (ULB), Evolutionary Biology & Ecology, Brussels, Belgium.
6
CNRS, Université Côte d'Azur, Institute of Molecular and Cellular Pharmacology, France.
7
MIAT, Université de Toulouse, INRA, Castanet Tolosan, France.
8
Université d'Evry Val d'Essonne, UMR 8030, Evry, France.
9
Centre National de Recherche Scientifique (CNRS), UMR 8030, Evry, France.

Abstract

Root-knot nematodes (genus Meloidogyne) exhibit a diversity of reproductive modes ranging from obligatory sexual to fully asexual reproduction. Intriguingly, the most widespread and devastating species to global agriculture are those that reproduce asexually, without meiosis. To disentangle this surprising parasitic success despite the absence of sex and genetic exchanges, we have sequenced and assembled the genomes of three obligatory ameiotic and asexual Meloidogyne. We have compared them to those of relatives able to perform meiosis and sexual reproduction. We show that the genomes of ameiotic asexual Meloidogyne are large, polyploid and made of duplicated regions with a high within-species average nucleotide divergence of ~8%. Phylogenomic analysis of the genes present in these duplicated regions suggests that they originated from multiple hybridization events and are thus homoeologs. We found that up to 22% of homoeologous gene pairs were under positive selection and these genes covered a wide spectrum of predicted functional categories. To biologically assess functional divergence, we compared expression patterns of homoeologous gene pairs across developmental life stages using an RNAseq approach in the most economically important asexually-reproducing nematode. We showed that >60% of homoeologous gene pairs display diverged expression patterns. These results suggest a substantial functional impact of the genome structure. Contrasting with high within-species nuclear genome divergence, mitochondrial genome divergence between the three ameiotic asexuals was very low, signifying that these putative hybrids share a recent common maternal ancestor. Transposable elements (TE) cover a ~1.7 times higher proportion of the genomes of the ameiotic asexual Meloidogyne compared to the sexual relative and might also participate in their plasticity. The intriguing parasitic success of asexually-reproducing Meloidogyne species could be partly explained by their TE-rich composite genomes, resulting from allopolyploidization events, and promoting plasticity and functional divergence between gene copies in the absence of sex and meiosis.

Comment in

PMID:
28594822
PMCID:
PMC5465968
DOI:
10.1371/journal.pgen.1006777
[Indexed for MEDLINE]
Free PMC Article

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