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SUMMARY: The formation of adventitious roots (ARs) derived from hypocotyl is the most important morphological adaptation to waterlogging stress in Cucumis sativus (cucumber). Our previous study showed that cucumbers with the gene CsARN6.1, encoding an AAA ATPase domain‐containing protein, were more tolerant to waterlogging through increased AR formation. However, the apparent function of CsARN6.1 remained unknown. Here, we showed that the CsARN6.1 signal was predominantly observed throughout the cambium of hypocotyls, where de novo AR primordia are formed upon waterlogging treatment. The silencing of CsARN6.1 expression by virus‐induced gene silencing and CRISPR/Cas9 technologies adversely affects the formation of ARs under conditions of waterlogging. Waterlogging treatment significantly induced ethylene production, thus upregulating CsEIL3 expression, which encodes a putative transcription factor involved in ethylene signaling. Furthermore, yeast one‐hybrid, electrophoretic mobility assay and transient expression analyses showed that CsEIL3 binds directly to the CsARN6.1 promoter to initiate its expression. CsARN6.1 was found to interact with CsPrx5, a waterlogging‐responsive class‐III peroxidase that enhanced H2O2 production and increased AR formation. These data provide insights into understanding the molecular mechanisms of AAA ATPase domain‐containing protein and uncover a molecular mechanism that links ethylene signaling with the formation of ARs triggered by waterlogging. Significance Statement: The AAA ATPase domain‐containing protein CsARN6.1 is required for waterlogging stress tolerance, where it regulates adventitious root (AR) formation. However, the functional relevance of this gene remained unknown. Our results reveal that in cucumber, a CsEIL3‐CsARN6.1 regulatory module confers AR formation through H2O2 production, mediated by CsPrx5. [ABSTRACT FROM AUTHOR]

Waterlogging is a severe environmental stress that causes severe crop productivity losses. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots (ARs) that enhance gas exchange. Little is known about the role of light and sugars in the waterlogging‐induced production of ARs. The role of these factors in AR production was therefore studied in cucumber seedlings grown in the absence or presence of waterlogging and different light conditions. The effect of photosynthesis was studied by removing the shoots of the seedlings and replacing them with exogenous applications of sucrose or stachyose. Shoot removal inhibited AR emergence and elongation. However, the exogenous application of sugars fully restored AR emergence and partially restored root elongation. The exogenous application of a synthetic auxin restored AR emergence but not AR elongation. Transcriptome profiling analysis was used to determine the effects of light on gene expression in the hypocotyls under these conditions. The levels of transcripts encoding proteins involved in auxin transport and signalling were higher in the light and following the exogenous application of sucrose and stachyose. These results show that the waterlogging‐induced emergence of ARs is regulated by the interaction between sugars and auxin, whereas AR elongation depends only on sugars alone. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots to enhance gas exchange. However, the molecular mechanisms underlying waterlogging‐induced adventitious root formation is less studied. The present results indicate that waterlogging‐induced adventitious root formation is regulated by an interaction of sugars (especially stachyose and sucrose) and auxin signalling. Sugars act as molecular signals that are mediated by auxin transport and response signalling to induce the adventitious root emergence, and as energy resources for adventitious root elongation. [ABSTRACT FROM AUTHOR]

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1‐methylcyclopropene (1‐MCP), the auxin transport inhibitor 1‐naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin‐induced AR formation was inhibited by 1‐MCP, although ethylene‐induced AR formation was not inhibited by NPA. Both ethylene‐ and auxin‐induced AR formation were counteracted by DPI. These results indicate that auxin‐induced AR formation is dependent on ethylene, whereas ethylene‐induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene‐ and auxin‐induced AR formation in cucumber plants. In response to waterlogging, many plants develop adventitious roots (ARs) to enhance gas exchange and nutrient uptake. Auxin, ethylene, and reactive oxygen species (ROS) all take part in this process, but little is known about how they interact. In cucumber, we report that auxin‐induced AR formation is dependent on ethylene, whereas ethylene‐induced AR formation is independent of auxin. Both ethylene and auxin upregulated genes involved in ROS production, which finally lead to AR formation. These results demonstrate the importance of crosstalk among ethylene, auxin, and ROS and show that the crosstalk is generally different in different plants. [ABSTRACT FROM AUTHOR]

Flooding of vegetable crop fields along the Yangtze River basin in China has been an annual occurrence; therefore the cultivation of tolerant varieties has become one of the most promising control strategies. Our objective was to investigate the inheritance of waterlogging tolerance of cucumber at the early stage of growth with two cucumber parents consisting of PW0832 (tolerant) and PW0801 (susceptible). In 2006, 4-weeks-old potted plants of P1, P2, F1, F2, B1 and B2 generations were subjected to one week waterlogged stress, control plants were not flooded. The simple additive model explained the variations of tolerance score (TOL) adventitious root formation (ARF) and waterlogged root dry weight (RDW) while the additive-dominance model explained the control treatment of RDW. Non-allelic interactions were detected for waterlogged vine length (VLH) and root length (RLH). Complementary epistasis occurred in waterlogged VLH while additive × additive, additive × dominance and dominance × dominance epistastic effects were significant for waterlogged RLH. Transgressive segregation was also observed in most of the traits in the F2 generation indicating some alleles are dispersed in the parents used in this study. The estimates of narrow-sense heritabilities for TOL and ARF were moderately high. Backcross of F1 to both parents in ARF, waterlogged SDW and waterlogged RDW showed good convergence of genes in the B2. These results suggest that it should be possible to develop varieties with high levels of tolerance by selecting transgressive segregants in this cross. [ABSTRACT FROM AUTHOR]