Rorippa islandica: a genetically accessible dicot model system to study flooding tolerance.

Most crop species cannot survive prolonged flooding events. Within the Cardamineae tribe of the Brassicaceae family, several wild species display high flooding tolerance and are therefore attractive study systems to unravel tolerance mechanisms. However, the genetic recalcitrance of many of these species has prevented detailed mechanistic studies of observed tolerance traits. Here, Rorippa islandica was identified as a genetically accessible diploid species with high submergence tolerance. Comparison of its submergence transcriptome with that of another diploid species from the same genus, the submergence-sensitive R. stylosa, revealed a strong and partially overlapping transcriptomic response to 48 h submergence. It also revealed RiBCA3 as a potential tolerance gene contributing to the higher submergence survival of R. islandica. Successful CRISPR-Cas9-mediated knockout of RiBCA3 confirmed the suitability of this species for genetic transformation. However, although it was hypothesized that RiBCA3 might have an important function in carbon fixation under water, no differences in submergence survival or underwater photosynthesis were observed between wild-type and bca3 knockout lines. The molecular mechanisms of submergence tolerance of Rorippa islandica are therefore not yet understood. This work demonstrates the suitability of Rorippa islandica for molecular genetics studies and presents a promising dicot model for investigation of underlying tolerance mechanisms, especially for comparative studies with Arabidopsis. This species might contribute to knowledge on flood tolerance in dicots, particularly Brassica oilseed crops and vegetables, while current knowledge is based primarily on rice (a monocot) studies.