Group leader KCGEB, UAEU Al Ain, Abu Dhabi, United Arab Emirates
Drought and salinity are two major environmental challenges that affect plant growth and productivity. The ubiquitin-proteasome system (UPS)-mediated proteolysis is vital in maintaining cellular homeostasis and is involved in stress signaling in plants by regulating the abundance of proteins. E3 ubiquitin ligases control target recognition and ubiquitin transfer. RING-type E3 ligases play a crucial role in ubiquitin-mediated proteolysis, which facilitates plant responses to abiotic stresses. We present the first functional characterization of novel RING-type E3 ligases from Sesuvium verrucosum, SvRNF170 and SvRNF185, under abiotic stresses in plants. These E3 ligases are ubiquitously expressed in all tissues and are induced under salt stress. They share high similarities with their human orthologues, which are involved in endoplasmic reticulum-associated degradation (ERAD). The ubiquitination analyses demonstrate the ligase activity of SvRNF170 and SvRNF185 and highlight the essential role of the RING domain. Subcellular localization studies confirmed that both SvRNF170 and SvRNF185 proteins are associated with the endoplasmic reticulum (ER) membrane. Furthermore, overexpression of SvRNF170 and SvRNF185 conferred salt, osmotic, and ER stress tolerance in Arabidopsis thaliana. Their regulation of ER stress-responsive gene expression combined with the identification of interacting proteins involved in the ERAD pathway indicate their involvement in mediating the ER stress response and their potential role in the ERAD pathway. These studies provide the first functional investigation of two evolutionarily conserved E3 ligases and contribute to our knowledge of the regulatory mechanisms under stress conditions.