GFP-labelled Rubisco and aspartate aminotransferase are present in plastid stromules and traffic between plastids

Plastid stromules are membrane-bound protrusions of the plastid envelope that contain soluble stroma. Stromules are often found connecting plastids within a cell and fluorescence recovery after photobleaching (FRAP) experiments have demonstrated that green fluorescent protein (GFP) can move between plastids via these connections. In this report, the ability of endogenous plastid proteins to travel through stromules was investigated. The motility of GFP-labelled plastid aspartate aminotransferase and the Rubisco small subunit was studied in stromules by FRAP. Both fusion proteins assemble into protein complexes that appear to behave similarly to their endogenous counterparts. In addition, both enzymes are capable of trafficking between plastids via stromules.