Physiological and Transcriptomic Characterization of Sea-Wheatgrass-Derived Waterlogging Tolerance in Wheat

Waterlogging, causing hypoxia stress and nitrogen depletion in the rhizosphere, has been an increasing threat to wheat production. We developed a wheat–sea wheatgrass (SWG) amphiploid showing superior tolerance to waterlogging and low nitrogen. Validated in deoxygenated agar medium for three weeks, hypoxia stress reduced the dry matter of the wheat parent by 40% but had little effect on the growth of the amphiploid. To understand the underlying mechanisms, we comparatively analyzed the wheat–SWG amphiploid and its wheat parent grown in aerated and hypoxic solutions for physiological traits and root transcriptomes. Compared with its wheat parent, the amphiploid showed less magnitude in forming root porosity and barrier to radial oxygen loss, two important mechanisms for internal O(2) movement to the apex, and downregulation of genes for ethylene, lignin, and reactive oxygen species. In another aspect, however, hypoxia stress upregulated the nitrate assimilation/reduction pathway in amphiploid and induced accumulation of nitric oxide, a byproduct of nitrate reduction, in its root tips, and the amphiploid maintained much higher metabolic activity in its root system compared with its wheat parent. Taken together, our research suggested that enhanced nitrate assimilation and reduction and accumulation of nitric oxide play important roles in the SWG-derived waterlogging tolerance.