The major-effect quantitative trait locus CsARN6.1 encodes an AAA ATPase domain-containing protein that is associated with waterlogging stress tolerance by promoting adventitious root formation.

In plants, the formation of hypocotyl-derived adventitious roots (ARs) is an important morphological acclimation to waterlogging stress; however, its genetic basis remains fragmentary. Here, through combined use of bulked segregant analysis-based whole-genome sequencing, SNP haplotyping and fine genetic mapping, we identified a candidate gene for a major-effect QTL, ARN6.1, that was responsible for waterlogging tolerance due to increased AR formation in the cucumber line Zaoer-N. Through multiple lines of evidence, we show that CsARN6.1 is the most possible candidate for ARN6.1 which encodes an AAA ATPase. The increased formation of ARs under waterlogging in Zaoer-N could be attributed to a non-synonymous SNP in the coiled-coil domain region of this gene. CsARN6.1 increases the number of ARs via its ATPase activity. Ectopic expression of CsARN6.1 in Arabidopsis resulted in better rooting ability and lateral root development in transgenic plants. Transgenic cucumber expressing the CsARN6.1^Asp allele from Zaoer-N exhibited a significant increase in number of ARs compared with the wild type expressing the allele from Pepino under waterlogging conditions. Taken together, these data support that the AAA ATPase gene CsARN6.1 has an important role in increasing cucumber AR formation and waterlogging tolerance.

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