Membrane lipid-driven thylakoid biogenesis coordinating chlorophyll synthesis and expression of photosynthetic proteins.

Chloroplasts in seed plants differentiate from proplastids or, occasionally, from other types of plastids. The development of the thylakoid membrane (TM) is a key process in chloroplast biogenesis, enabling plants to perform photosynthesis. The TM is a lipid bilayer membrane system densely packed with photosynthetic protein-cofactor complexes, and its formation requires the coordinated synthesis of membrane lipids, photosynthetic proteins, and cofactors particularly chlorophyll. During chloroplast biogenesis, membrane lipids are synthesized in the envelope membranes and transferred to the TM through yet unknown mechanisms. Chlorophyll biosynthesis and the synthesis of plastid-encoded proteins also occur in association with membranes, although their precise suborganellar sites, especially during early chloroplast development, remain unclear. In this review, we discuss the roles of the chloroplast envelope and internal membranes as potential origins of the TM during chloroplast development and then summarize current knowledge on the biosynthetic pathways of plastid membrane lipids, chlorophyll, and photosynthetic proteins. We further highlight recent findings on how plastid lipid biosynthesis contributes to the synthesis of chlorophyll and plastid-encoded proteins, as well as to the expression of photosynthesis-associated nuclear-encoded genes via plastid-to-nucleus retrograde signaling. Finally, we propose that plastid lipid biosynthesis triggers chloroplast biogenesis by initiating and coordinating membrane-associated processes required for TM formation.