Tomato bushy stunt virus (TBSV) causes extensive inward vesiculations of the boundary membrane of host plant peroxisomes, resulting in the formation of peroxisomal multivesicular bodies. McCartney et al. (pages 3513–3531) show that the TBSV 33-kD replication protein (p33) by itself causes alteration and aggregation of peroxisomes and relocalization of p33 and resident peroxisomal membrane proteins to the peroxisomal endoplasmic reticulum (pER). Mutational analysis of p33 showed that its intracellular sorting is mediated by several targeting signals, including a pER targeting motif similar to one involved in retrieval of escaped ER membrane proteins from the Golgi. The results provide insight into virus-induced intracellular rearrangements and reveal a peroxisome-to-pER sorting pathway that raises mechanistic questions regarding the biogenesis of peroxisomes in plants. The cover shows an immunofluorescence micrograph illustrating the localization of the TBSV replicase proteins p33 and p92 to peroxisomal multivesicular bodies (green) and concanavalin A-stained ER (red) in a transformed tobacco BY-2 cell.