On the Cover: Endoplasmic Reticulum Export Site Differentiation in Plant Cells

Export of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus is an essential process to the life of a cell. Protein export from the ER is dependent on the localized polymerization of protein machinery called COPII that shapes the ER membrane into transport carriers. The COPII machinery operates at specialized ER subdomains—the ER export sites (ERES). By combining biochemical and live cell-imaging techniques, Hanton et al. (pp. 1640–1650) demonstrate that in plants the assembly of COPII coat proteins is not a constitutive feature of ERES. In particular, they show that COPII activity at ERES responds to the plant cell's need to secrete by recruiting COPII coat to ERES and by differentiating new ERES. The cover image shows the distribution of the known fluorescent ERES marker YFP-Sec24 (magenta) and ER/Golgi marker ERD2-GFP (green). In the overlaid image, it is possible to see that the Sec24-ERES structures are distributed at the peri-Golgi area in Arabidopsis leaves. This distribution is similar to that in tobacco leaves. Images were produced by Loren A. Matheson, assisted by Marlene Cameron.