Figure 3.

Network of the regulation of submergence and waterlogging growth, adaptation, and metabolic responses by ethylene, low oxygen, ROS, and NO. Elongation growth is controlled by GA-mediated pathways, which act downstream of ethylene and ABA. In rice group VII ERFs, SK1 and SK2 positively regulate internode elongation, presumably through the stimulation of GA-mediated starch consumption and elongation growth. Conversely, the rice group VII ERF SUB1A inhibits shoot elongation by maintaining levels of the transcription factors SLR1 and SLRL1 to counterbalance GA responsiveness. In some species, underwater elongation involves hyponastic growth or the upward curvature of the leaf petiole or blade. The development of adventitious roots and aerenchyma is regulated by ethylene and ROS. The presence of a thin gas film on underwater leaves helps maintain photosynthesis and, therefore, starch production. Oxygen deficiency dampens ATP energy levels. In germinating seeds of rice, CIPK15 promotes SnRK1 activity to enhance carbohydrate catabolism. Low-oxygen stress enhances the consumption of soluble carbohydrates in anaerobic reactions that generate ATP to maintain cellular homeostasis. In Arabidopsis, the up-regulation of genes encoding enzymes required for anaerobic metabolism requires the stabilization of group VII ERFs. This occurs conditionally, as oxygen levels decline, by inhibition of the Arg/N branch of the N-end rule pathway of targeted proteolysis. All group VII ERFs of the Columbia-0 ecotype possess an N terminus that confers instability under aerated conditions and stability under oxygen deficiency. Orange, hormones/signaling molecules; green, physiological changes; purple, proteins/pathways; blue, metabolic components.