An Investigation into Plastid Localized Lipases at Membrane Contact Sites with the Endoplasmic Reticulum using Live-Imaging
Fluorescent protein-based imaging revealed that transient tubules extend and retract from plastids. One hypothesis is that tubulation is a result of pulling force from the endoplasmic reticulum (ER) exerted at membrane contact sites (MCSs). A Brassica napus chloroplast lipase protein 1 (BnCLIP) appeared to mark ER-plastid MCSs; therefore plastids, ER and BnCLIP were observed in live transgenic plants using confocal microscopy. This study found that BnCLIP marked sites where the ER and plastids maintained prolonged contact and where plastid tubules extended by apparent pulling force from the ER. BnCLIP frequency increased significantly following phosphate starvation but not 40mM sucrose treatment. The potential for native Arabidopsis thaliana lipase proteins to localize in a similar manner was explored. This study provides the first demonstration of the role that plastid-ER MCSs play in living cells to modulate the shape and dynamic behaviour of plastids.