Biochemistry, Department of


Date of this Version



PNAS Early Edition


Copyright 2016 Kelly et al.


Galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol

(DGDG)] are the hallmark lipids of photosynthetic

membranes. The galactolipid synthases MGD1 and DGD1

catalyze consecutive galactosyltransfer reactions but localize to the

inner and outer chloroplast envelopes, respectively, necessitating

intermembrane lipid transfer. Here we show that the N-terminal

sequence of DGD1 (NDGD1) is required for galactolipid transfer

between the envelopes. Different diglycosyllipid synthases (DGD1,

DGD2, and Chloroflexus glucosyltransferase) were introduced into

the dgd1-1 mutant of Arabidopsis in fusion with N-terminal extensions

(NDGD1 and NDGD2) targeting to the outer envelope. Reconstruction

of DGDG synthesis in the outer envelope membrane was

observed only with diglycosyllipid synthase fusion proteins carrying

NDGD1, indicating that NDGD1 enables galactolipid translocation

between envelopes. NDGD1 binds to phosphatidic acid (PA) in membranes

and mediates PA-dependent membrane fusion in vitro.

These findings provide a mechanism for the sorting and selective

channeling of lipid precursors between the galactolipid pools of the

two envelope membranes.