Comparative genomics of the root knot nematodes: tales of sex, hybridisation, and adaptation

Abstract

Root knot nematodes (RKN) can infect most of the world’s agricultural crop species and are among the most important of all plant pathogens. As yet however we have little understanding of their origins or the genomic basis of this extreme polyphagy. It has been suggested that the most damaging pathogens have originated from interspecific hybridisations between unknown parental taxa. We have sequenced the genome of Meloidogyne floridensis, and use comparative evolutionary genomics of RKN to test the hypothesis that this species was involved in the hybrid origin of the agriculturally important species Meloidogyne incognita. Phylogenomic analyses of gene families indicate that RKN species may have very complex origins involving the mixing of several parental genomes by hybridisation. This comparative genomic analysis provides a compelling example of the importance and complexity of hybridisation in generating animal species diversity more generally. I speculate that the extreme polyphagy of some RKN, and their success in agricultural environments, may be related to this hybridisation, producing transgressive variation on which natural selection can act. Finally I discuss what the future of agricultural population genomics might hold.