Cargo proteins traverse the Golgi apparatus by remaining within the maturing cisternae. Studies in yeast via live imaging have made the cisternal maturation model more popular (Losev et al., 2006; Matsuura-Tokita et al., 2006). Regarding the functional diversity of COPI, recent electron tomography studies in Arabidopsis and algal cells identified two structurally distinct types of COPI vesicles, t