Genetic basis of resistance in hosts facing alternative infection strategies by a virulent bacterial pathogen

Abstract

Having alternative infection routes is thought to help parasites circumvent host resistance, provided that these routes are associated with different host resistance loci. This study examines whether alternate infection routes of the parasitePasteuria ramosaare linked to distinct resistance loci in its crustacean host,Daphnia magna. We focus on theP. ramosaisolate P15, which can attach and penetrate the host through either the hindgut or the foregut. Using a global panel of 174D. magnagenotypes supplemented with breeding experiments, we analyzed resistance patterns for each of these infection routes. Our findings confirm our hypothesis: inD. magna, hindgut attachment is determined by the D locus, while foregut attachment is controlled by a newly identified G locus. We established a gene model for the G locus that indicated Mendelian segregation and epistatic interaction with at least one other resistance locus forP. ramosa, the C locus. Using genomic Pool-sequencing data, we localized the G locus within a known Pasteuria Resistance Complex on chromosome 4 ofD. magna, whereas the D locus is on chromosome 7. Two candidate genes for the G locus, belonging to the Glycosyltransferase gene family, were identified. Our study sheds new light on host-parasite coevolution and enhances our understanding of how parasites evolve infection strategies.