Soybean RING‐type E3 ligase GmCHYR16 ubiquitinates the GmERF71 transcription factor for degradation to negatively regulate bicarbonate stress tolerance

Plant AP2/ERF (APETALA2/ethylene response factor) transcription factors are key regulators of environmental stress tolerance. We previously characterized that the wild soybean ERF71 transcription factor conferred bicarbonate stress tolerance; however, the underlying mechanism still remains elusive. Here, multiple approaches were used to identify the E3 ubiquitin ligase GmCHYR16 as an interactor of GmERF71. Ubiquitination and protein degradation of GmERF71 mediated by GmCHYR16 were then analyzed. Overexpression transgenic lines were generated to evaluate the function of GmCHYR16 and GmERF71 in bicarbonate stress response. GmCHYR16 interacts with GmERF71. GmERF71 proteins undergo ubiquitination and 26S proteasome-mediated degradation, and GmCHYR16 mediates the ubiquitination of GmERF71 for degradation. The GmCHYR16-mediated ubiquitination and proteasome-dependent degradation of GmERF71 are reduced under bicarbonate stress. GmCHYR16 expression in transgenic Arabidopsis, soybean hairy roots, and stable transgenic soybean reduces bicarbonate stress tolerance. GmERF71 degradation is decreased in the protein extracts of atchyr1/7 mutants, and atchyr1/7 mutants display higher bicarbonate tolerance. Overexpression of GmERF71 in transgenic soybean obviously increases bicarbonate tolerance, and GmCHYR16 reduces the bicarbonate tolerance of transgenic hairy root composite soybean plants by repressing GmERF71. Our results demonstrate that GmCHYR16 directly ubiquitinates GmERF71 for degradation and negatively regulates bicarbonate stress tolerance.