Signal motifs-dependent ER export of Qc-SNARE BET12 interacts with MEMB12 and affects PR1 trafficking in Arabidopsis

Abstract

SNAREs are well-known for their role in controlling membrane fusion, the final but crucial step for vesicular transport in eukaryotes. SNARE proteins contribute to various biological processes including pathogen defense, channel activity regulation as well as plant growth and development. Precise targeting of SNARE proteins to destined compartments is a prerequisite for their proper functioning. However, the underlying mechanism(s) for SNAREs targeting in plants remains obscure. Here we investigate the targeting mechanism of the Qc-SNARE BET12, which is involved in protein trafficking in the early secretory pathway. Two distinct signal motifs that are required for efficient BET12 ER export have been identified. Pull down assays and in vivo imaging have implicated a BET12-dependency on both the COPI and COPII pathways for its targeting. Further studies using an ER-export defective form of BET12 revealed the Golgi-localized Qb-SNARE MEMB12, a negative regulator of pathogenesis-related protein1 (PR1) secretion, as its interacting partner. Ectopic expression of BET12 showed no inhibition in the general ER-Golgi anterograde transport but caused intracellular accumulation of PR1, suggesting the regulatory role of BET12 in PR1 trafficking in Arabidopsis thaliana.