The stability and nuclear localization of the transcription factor RAP2.12 are dynamically regulated by oxygen concentration

Abstract

Plants often experience low oxygen conditions as the consequence of reduced oxygen availability in their environment or due to a high activity of respiratory metabolism. Recently, an oxygen sensing pathway was described in Arabidopsis thaliana which involves the migration of an ERF transcription factor (RAP2.12) from the plasma membrane to the nucleus upon hypoxia. Moreover, RAP2.12 protein level is controlled through an oxygen-dependent branch of the N-end rule pathway for proteasomal degradation. Inside the nucleus, RAP2.12 induces the expression of genes involved in the adaptation to reduced oxygen availability. In the present study, we describe the oxygen concentration and time-resolved characterization of RAP2.12 activity. A reduction of the oxygen availability to half the concentration in normal air is sufficient to trigger RAP2.12 relocalization into the nucleus, while nuclear accumulation correlates with the first induction of the molecular response to hypoxia. Nuclear presence of RAP2.12 may not only depend on relocalization of existing protein, but involves de novo synthesis of the transcription factor as well. After re-oxygenation of the tissue, degradation of RAP2.12 in the nucleus was observed within 3 h, concomitant with reduction in hypoxia responsive gene transcripts to normoxic levels.

Oxygen Sensing via the Ethylene Response Transcription Factor RAP2.12 Affects Plant Metabolism and Performance under Both Normoxia and Hypoxia

“…Protein stability of the ERF-VII family member RAP2.12 has been found to be strictly dependent on the oxygen concentration, being increased when oxygen is decreasing from 21 to below 10% (v/v; Kosmacz et al, 2015). While research into RAP2.12 mainly focused on its role to regulate anoxic gene expression, little is known on the impact of this oxygen-sensing system in regulating plant metabolism and growth.…”

“…RAP2.12 and Cys oxidases therefore act as an oxygen-sensing system in Arabidopsis plants, allowing expression of hypoxic genes to be strictly regulated in response to oxygen supply . When oxygen falls to concentrations below 10% (v/v), RAP2.12 is stabilized and relocated to the nucleus to induce hypoxic gene expression (Kosmacz et al, 2015). This is fine-tuned by an antagonistic interplay between RAP2.12 and the trihelix transcription factor HYPOXIA RESPONSE ATTENUATOR1 enabling a flexible response to fluctuating hypoxia .…”

“…Different members of subgroup VII ethylene-response factor (ERF) transcription factors have been identified to be involved in the regulation of hypoxic gene expression in Arabidopsis (Arabidopsis thaliana; Papdi et al, 2008;Hinz et al, 2010;Licausi et al, 2010Licausi et al, , 2011bGasch et al, 2016). One of these members, RAP2.12, has been found to be regulated by intracellular relocalization and protein stability in response to low oxygen concentrations (Gibbs et al, 2011, Licausi et al, 2011cKosmacz et al, 2015). Upon hypoxia, RAP2.12 moves from the plasma membrane into the nucleus to specifically activate the expression of anaerobic genes, such as PYRUVATE DECARBOXYLASE1 (PDC1) and ALCOHOL DEHYDROGENASE1 (ADH1) involved in ethanol fermentation, SUC SYNTHASE1 (SUS1) and SUS4 involved in carbohydrate degradation, and HEMOGLOBIN1 (HB1) involved most probably in scavenging of nitric oxide to promote conversion of NADH to NAD + (Licausi et al, 2011c).…”

“…In normoxia (21% v/v oxygen) and after reoxygenation, RAP2.12 is targeted to proteasome-mediated proteolysis via the oxygen-dependent branch of the N-end-rule pathway to down-regulate the hypoxic response (Licausi et al, 2011c, Kosmacz et al, 2015. The presence of molecular oxygen leads to oxidation of the penultimate Cys in the N terminus of RAP2.12 by specific plant Cys oxidases, targeting RAP2.12 to proteasomal degradation and leading to its destabilization (Weits et al, 2014).…”

Root Bending Is Antagonistically Affected by Hypoxia and ERF-Mediated Transcription via Auxin Signaling

“…In wild-type seedlings, the angle of hypoxia-induced root bending was intermediary to that observed in HRE2ox1 and rap2.12-1 or erfVII seedlings, indicating that the growth angle of hypoxic roots is regulated by ERFVII activity in a dose-dependent manner making ERFVIIs a potential hub for signal integration. Environmental signals other than the oxygen concentration might determine root growth direction by controlling RAP2.12 activity through transcriptional regulation, protein stability, or subcellular localization (Licausi et al, 2011;Kosmacz et al, 2015).…”