This month, we're pleased to continue our series on plant cell biology with an article that focuses on the subject of membrane trafficking in plants. On page 100, Marci Surpin and Natasha Raikhel discuss the endomembrane system in plants — in particular, the plant vacuole, which is essential for vesicular trafficking and viability. It is clear that the endomembrane-trafficking system does not just deliver cargo — it's also intimately involved in signal transduction and development. And, new approaches described in this Review might help us to discover new connections between trafficking, plant development and signal transduction.

Important features of membrane-trafficking processes are sorting events, which are required to ensure that components are delivered to their correct destination. On page 110, Satajit Mayor and Howard Riezman review the sorting of glycosylphosphatidylinositol-anchored proteins. These proteins are made in the endoplasmic reticulum, but are found mainly on the plasma membrane. So, how are they sorted and transported through the secretory and numerous endocytic pathways? On page 121, Frederick R. Maxfield and Timothy E. McGraw discuss endocytic recycling. The pathways taken by endocytosed molecules can be remarkably complex and can involve a series of sorting events that occur in several organelles. The challenge is to understand the molecular basis of these events.

Finally, you would be forgiven for thinking that this month's front cover relates to our series on plant cell biology, but it was created with the process of decay in mind. On page 89, Lynne E. Maquat reviews the process of nonsense-mediated messenger RNA decay — a post-transcriptional mechanism that can be used by eukaryotic cells to control the quality of mRNA transcripts.