A Regulatory Cascade Involving Transcriptional and N-end Rule Pathways in Rice under SubmergenceThe rice SUB1A-1 gene, which encodes a group VII ethylene response factor (ERFVII) plays a pivotal role in rice survival under flooding stress. In Arabidopsis, five ERFVIIs play roles in regulating hypoxic responses. A characteristic feature of Arabidopsis ERFVIIs is a destabilizing N-terminus, which functions as an N-degron that targets them for degradation via the oxygen-dependent N-end rule pathway of proteolysis, but permits their stabilization during hypoxia for hypoxia-responsive signaling. Despite having the canonical N-degron sequence, SUB1A-1 is not under N-end rule regulation, suggesting a distinct hypoxia signaling pathway in rice during submergence. Herein we show that two other rice ERFVIIs, ERF66 and ERF67, are directly transcriptionally up-regulated by SUB1A-1 under submergence. In contrast to SUB1A-1, ERF66 and ERF67 are substrates of the N-end rule pathway, which are stabilized under hypoxia and may be responsible for triggering a stronger transcriptional response to promote submergence survival. Overexpression ERF66 or ERF67 leads to activation of anaerobic survival genes and enhanced submergence tolerance. Using structural and protein-interaction analyses, we show that the C-terminus of SUB1A-1 prevents its degradation via the N-end rule and directly interacts with the SUB1A-1 N-terminus, which may explain enhanced stability of SUB1A-1 despite bearing an N-degron sequence. In summary, our results suggest that SUB1A-1, ERF66 and ERF67 form a regulatory cascade involving transcriptional and N-end rule control, which allows rice to distinguish flooding from other SUB1A-1-regulated stresses.
Co-researchers:Meng-Chiao Ho, Institute of Biological Chemistry