Rorippa islandica is a genetically accessible dicot model system to study flooding tolerance
Most crop species cannot survive flooding events for a long period of time. However, within the Cardamineae tribe of the Brassicaceae family, there exist several wild species with high flooding tolerance.  Here, Rorippa islandica was identified as a genetically accessible diploid species with high submergence tolerance. Another diploid species from the same genus, R. stylosa, showed similar submergence sensitivity compared with Arabidopsis. Both species exhibited a strong and partially overlapping transcriptomic response to submergence within the first 48 hours of stress, including carbon-starvation and ethylene-responsive marker genes. We demonstrate that R. islandica can be transformed via floral dip, but with rather low frequency. The successful CRISPR-Cas9-mediated knockout of RiBCA3 confirms 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 wildtype and bca3 knockout lines. The molecular mechanisms of submergence tolerance of Rorippa islandica are therefore not understood yet. The data indicate that illumination and therefore photosynthesis-associated processes must be the basis for superior submergence survival. This work suggests that Rorippa islandica is a promising dicot model to further investigate the underlying tolerance mechanisms. Overall design: Submergence experiments were conducted in transparent plastic boxes, filled with tap water the day before. Control plants were kept in empty boxes. After 24 and 48 hours young healthy leaves were harvested for RNAsequenicing for both Rorippa stylosa and Rorippa islandica. Plants were grown in pots 3 to 4 weeks prior start of the experiment.