Fig. 2. Abiotic stress signalings and the related E3 ligases. (A, B) Schematic representation of water-deficit stress signaling in the presence or absence of ABA (A) and the involvement of E3 ligases in ABA-mediated drought signaling via AREB/ABF/ ABI5/DPBF bZIP subfamily (B). ‘Substrate modification’ indicates either negative regulation by polyubiquitination or positive regulation by monou-biquitination. (C, D) Simplified scheme of cold signaling pathway (C) and the negative regulation of ICE1 by HOS1 E3 ligase (D). The protein stability of ICE1 is negatively regulated by ubiquitination, whereas its activity is positively regulated by phosphorylation and sumoylation. The activated ICE1 binds to MYCRS in the promoter region of CBF3 and then positively regulates the expression of CBF3 and its downstream genes. ‘P’ and ‘S’ indicates phosphate and small ubiquitin-related modifier (SUMO), respectively.