EL5 is involved in root development as an anti-cell death ubiquitin ligase

Ubiquitin ligase (E3) plays a central role in substrate recognition during ubiquitination, a post-translational modification of proteins. Rice EL5 is an E3 with a RING-H2 finger domain (RFD) and its transcript is upregulated by a chitin elicitor. The EL5-RFD has been intensively studied and demonstrated to exhibit E3 activity. Its three-dimensional structure was determined for the first time in plant E3, and the amino acid residues required for the interaction with the ubiquitin-conjugating enzyme (E2) were identified. Recent analyses revealed that EL5 plays a crucial role as an E3 in the maintenance of cell viability during root development in rice. In this addendum, we report that the EL5-RFD catalyzes polyubiquitination via the Lys48 residue of ubiquitin. We also discuss the possible role of EL5 as an anti-cell death enzyme. We hypothesize that EL5 might be responsible for mediating the degradation of cytotoxic proteins produced in root cells after the actions of phytohormones.