Candidate genes for adaptation to an aquatic habitat recovered from Ranunculus bungei and Ranunculus sceleratus

The molecular mechanisms responsible for plant adaptations to aquatic habitats remain poorly known. In this study, we aimed to detect selection on orthologous genes among the submerged aquatic plant Ranunculus bungei, semi-aquatic R. sceleratus, and terrestrial R. brotherusii and R. cantoniensis, in order to identify candidate genes involved in the adaptive transition from terrestrial habitats to aquatic habitats and if they differ between R. bungei and R. sceleratus. We used 884 previously reported 1:1:1:1 orthologous genes among the four species (one ortholog is represented in each species). We identified 177 genes of R. bungei and R. sceleratus that are potentially under positive selection. Among them, a set of candidate genes for adaptation to an aquatic habitat were recognized. These include several genes that are associated with photosynthesis, vacuoles, ethylene and oxygen receptors, and aerenchyma formation. Gene Ontology analyses suggest that the submerged R. bungei has a higher percentage of positively selected genes associated with the chloroplast and other plastids, while the semi-aquatic R. sceleratus has a higher percentage associated with metabolic processes. This study represents a step forward towards understanding the molecular mechanism of plant adaptations to aquatic habitats.