RING1 E3 ligase localizes to plasma membrane lipid rafts to trigger FB1-induced programmed cell death in Arabidopsis.

Ubiquitination plays important roles in plant development, including programmed cell death. Here, we characterize a novel membrane-bound RING motif protein, encoded by RING1, that is expressed at a low level in all Arabidopsis tissues but can be upregulated by fumonisin B1 (FB1) treatment and pathogen infection. RING1 displays E3 ubiquitin ligase activity in vitro, which is dependent on the integrity of the RING motif. GFP fusion protein localization and cell fractionation experiments show that this E3 ligase is associated with the lipid rafts of plasma membranes. Knock-down of RING1 transcripts using artificial microRNA (amiR-R1(159)) leads to FB1 hyposensitivity, but overexpression of RING1 confers hypersensitivity. Additionally, expression of the pathogenesis-related 1 (PR-1) gene is lower and delayed in amiR-R1(159) plants compared with wild-type and RING1-overexpressing plants. The FB1 hyposensitivity of amiR-R1(159) plants can be rescued by expression of cleavage-resistant RING1mut transcripts. Our results suggest that RING1 acts as a signal from the plasma membrane lipid rafts to trigger the FB1-induced plant programmed cell death pathway.