A Recently Formed Triploid Cardamine insueta Inherits Leaf Vivipary and Submergence Tolerance Traits of Parents

Contemporary speciation provides a unique opportunity to directly observe the traits and environmental responses of a new species. is an allotriploid species that appeared within the past 150 years in a Swiss village, Urnerboden. In contrast to its two progenitor species, and that live in wet and open habitats, respectively, is found in-between their habitats with temporal water level fluctuation. This triploid species propagates clonally and serves as a triploid bridge to form higher ploidy species. Although niche separation is observed in field studies, the mechanisms underlying the environmental robustness of are not clear. To characterize responses to a fluctuating environment, we performed a time-course analysis of homeolog gene expression in in response to submergence treatment. For this purpose, the two parental ( and ) genome sequences were assembled with a reference-guided approach, and homeolog-specific gene expression was quantified using HomeoRoq software. We found that and initiated vegetative propagation by forming ectopic meristems on leaves, while did not. We examined homeolog-specific gene expression of three species at nine time points during the treatment. The genome-wide expression ratio of homeolog pairs was 2:1 over the time-course, consistent with the ploidy number. By searching the genes with high coefficient of variation of expression over time-course transcriptome data, we found many known key transcriptional factors related to meristem development and formation upregulated in both and -homeolog of , but not in . Moreover, some -homeologs of these genes were also upregulated in the triploid, suggesting -regulation. In turn, Gene Ontology analysis suggested that the expression pattern of submergence tolerant genes in the triploid was inherited from . These results suggest that the triploid combined advantageous patterns of parental transcriptomes to contribute to its establishment in a new niche along a water-usage gradient.