DGTS overproduced in seed plants is excluded from plastid membranes and promotes endomembrane expansion

Plants and algae must adapt to environmental changes, facing various stresses that negatively impact their growth and development. One common stress is phosphate (Pi) deficiency, which is often in limiting quantity in the environment. In response to Pi deficiency, these organisms increase Pi uptake and remobilize intracellular Pi. Phospholipids are degraded to provide Pi and replaced by non-phosphorous lipids, such as glycolipids or betaine lipids. During the evolution, seed plants lost their capacity to synthesize betaine lipid. By expressing BTA1 genes, involved in the synthesis of diacylglyceryl-N,N,N-trimethyl-homoserine (DGTS), from different species, our work shows that DGTS can be produced in seed plants. In Arabidopsis, expressing BTA1 under a phosphate starvation-inducible promoter resulted in limited DGTS production without having any impact on plant growth or lipid remodeling. In transient expression systems in Nicotiana benthamiana, leaves were able to accumulate DGTS up to 20 % of their glycerolipid content at a slight expense of galactolipid and phospholipid production. At the subcellular level, we showed that DGTS is absent from plastid and seems to be enriched in endomembrane, driving an ER membrane proliferation. Finally, DGTS synthesis pathway seems to compete with PC synthesis via the Kennedy pathway but does not seem to be derived from PC diacylglycerol backbone and therefore does not interfere with the eukaryotic pathway involved in galactolipid synthesis.