Transient increase of phosphatidylcholine in plant cells in response to phosphate deprivation

Abstract

In plants, phosphate deprivation is normally known to decrease the phospholipid content consistent with a mobilization of the phosphate reserve, and conversely to increase nonphosphorous membrane lipids such as digalactosyldiacylglycerol. We report here that unexpectedly, at an early stage of phosphate starvation, phosphatidylcholine (PC) increases transiently. We also show that a signi¢cant pool of diacylglycerol (DAG) with the same fatty acid composition as that of PC is present and moreover increases in response to phosphate deprivation. The evolution of the molecular pro¢le of the newly synthesized galactolipids is compatible with a utilization of DAG accumulating from PC hydrolysis, achieved after selection of their acyl molecular species by the galactolipid synthesizing enzymes. ß

Glycerolipid transfer for the building of membranes in plant cells

“…Plastid and mitochondria membrane analyses were done respectively by [105] and [106]. synthesized in the chloroplast, formation of eukaryotic type galactolipids is dependent on the supply to the envelope of some PC derivatives formed in the ER: either diacylglycerol (DAG E) [6] or phosphatidate (PA E ) [37]. PAP converting PA to DAG is present in the envelope but only in the inner membrane.…”

“…Moreover a form of DGDG with specific fatty acids: 16:0 at glycerol sn1 position and 18:2 at sn2 position is especially enhanced [5,6]. Correlated to the lipid composition changes there is also a strong modification of the lipid distribution between membranes.…”

“…Upon phosphate deprivation, DGDG, a specific plastid lipid in standard conditions, was found in the plasma membrane [7,8], a membranous compartment disconnected from plastid membranes, but dynamically connected to the overall endomembrane system. Moreover, several lines of evidence have 6 shown that large amounts of DGDG are also present in mitochondria upon phosphate deprivation [9].…”

Role of phosphatidic acid in plant galactolipid synthesis

“…At an early stage of Pi deprivation a transient increase of PLDz2-enriched domains has been observed in tonoplast [63]. These domains are close to mitochondria and chloroplasts whose contacts are themselves increased at this stage and concomitant with galactolipid transfer from chloroplasts to mitochondria [19,64]. On the model of what has been observed in mammal cells, one can propose that PLDz2-produced PA can facilitate hemifusion of membranes and eventually remodelling of lipids between tonoplast, chloroplasts and mitochondria.…”

“…However, it is likely important to distinguish two phases in the lipid response to Pi deprivation. In an early stage, a transient increase of PC precedes the increase of galactolipid synthesis [19] and several phospholipases D and C such as PLDz1, PLDz2, NPC4 and NPC5 are highly overexpressed [20,21]. Therefore, this suggests that, at this stage, the Kennedy pathway actively contributes to remodelling of phospholipids, notably of PE into PC [19].…”