Ethylene signaling of hypoxic stress adaptation in Arabidopsis

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Plants are aerobic organisms. Too little oxygen (hypoxia) renders energy supply difficult and results in impaired plant metabolism. Common causes for hypoxic or even anoxic (lack of oxygen) conditions in plants are soil water logging and submergence. Depending on their ecological niche, plants are more or less well adapted to cope with low oxygen stress. The gaseous hormone ethylene rapidly accumulates in plant tissues upon flooding. Ethylene controls many adaptations that improve plant survival during flooding. In the model plant Arabidopsis thaliana ethylene regulates hyponastic petiole growth which helps to move the leaf above the water surface. Ethylene signaling in concert with hypoxia signaling furthermore regulates metabolic adaptation to low oxygen stress. AP2/ERF (apetala2/ethylene response factor) transcription factors were identified as key mediators of plant responses to flooding. The Arabidopsis thaliana ERFs RAP2.2 and ERF73 were previously shown to be regulated by hypoxia and by ethylene and both increase tolerance to low oxygen stress when overexpressed. The proposed project aims to elucidate the contribution of ethylene signaling to hypoxia adaptation via RAP2.2 and ERF73 in Arabidopsis thaliana. To this end, we will clarify if RAP2.2 and ERF73 have overlapping and/or unique functions. We will identify genes that are targeted by these transcription factors at normoxic and hypoxic conditions or when exposed to ethylene. And we will ask if RAP2.2 and ERF73 mediate the full ethylene response in hypoxic stress adaptation in Arabidopsis. We expect that our study will provide a major contribution to our understanding of ethylene signaling of hypoxic stress tolerance.