Submergence stress-induced hypocotyl elongation through ethylene signaling-mediated regulation of cortical microtubules in Arabidopsis.

Plant growth is significantly altered in response to submergence stress. However, the molecular mechanisms used by seedlings in response to this stress, especially for hypocotyl growth, are largely unknown in terrestrial plants such as Arabidopsis thaliana. The microtubule cytoskeleton participates in plant cell growth, but it remains unclear whether submergence-mediated plant growth involves the microtubule cytoskeleton. We demonstrated that in Arabidopsis submergence induced underwater hypocotyl elongation through the activation of ethylene signaling, which modulated cortical microtubule reorganization. Submergence enhanced ethylene signaling, which then activated and stabilized its downstream transcription factor, phytochrome-interacting factor 3 (PIF3), to promote hypocotyl elongation. In particular, the regulation of microtubule organization was important for this physiological process. Microtubule-destabilizing protein 60 (MDP60), which was previously identified as a downstream effector of PIF3, played a positive role in submergence-induced hypocotyl elongation. Submergence induced MDP60 expression through ethylene signaling. The effects of submergence on hypocotyl elongation and cortical microtubule reorganization were suppressed in mdp60 mutants. These data suggest a potential mechanism by which submergence activates ethylene signaling to promote underwater hypocotyl elongation via alteration of the microtubule cytoskeleton in Arabidopsis.