AUTHOR=Sun Jianqiang , Shimizu-Inatsugi Rie , Hofhuis Hugo , Shimizu Kentaro , Hay Angela , Shimizu Kentaro K. , Sese Jun 

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

JOURNAL=Frontiers in Genetics

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2020.567262

DOI=10.3389/fgene.2020.567262

ISSN=1664-8021

ABSTRACT=<p>Contemporary speciation provides a unique opportunity to directly observe the traits and environmental responses of a new species. <italic>Cardamine insueta</italic> is an allotriploid species that appeared within the past 150 years in a Swiss village, Urnerboden. In contrast to its two progenitor species, <italic>Cardamine amara</italic> and <italic>Cardamine rivularis</italic> that live in wet and open habitats, respectively, <italic>C. insueta</italic> 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 <italic>C. insueta</italic> are not clear. To characterize responses to a fluctuating environment, we performed a time-course analysis of homeolog gene expression in <italic>C. insueta</italic> in response to submergence treatment. For this purpose, the two parental (<italic>C. amara</italic> and <italic>C. rivularis</italic>) genome sequences were assembled with a reference-guided approach, and homeolog-specific gene expression was quantified using HomeoRoq software. We found that <italic>C. insueta</italic> and <italic>C. rivularis</italic> initiated vegetative propagation by forming ectopic meristems on leaves, while <italic>C. amara</italic> 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 <italic>C. rivularis</italic> and <italic>rivularis</italic>-homeolog of <italic>C. insueta</italic>, but not in <italic>C. amara</italic>. Moreover, some <italic>amara</italic>-homeologs of these genes were also upregulated in the triploid, suggesting <italic>trans</italic>-regulation. In turn, Gene Ontology analysis suggested that the expression pattern of submergence tolerant genes in the triploid was inherited from <italic>C. amara</italic>. These results suggest that the triploid <italic>C. insueta</italic> combined advantageous patterns of parental transcriptomes to contribute to its establishment in a new niche along a water-usage gradient.</p>