Changes in membrane lipid composition during Iron depletion and starvation in Chlamydomonas reinhardtii
C. reinhardtii cells exposed to abiotic stresses (e.g. iron-, nitrogen-, zinc- or phosphorus-deficiency) accumulate TAGs which are stored in lipid droplets. Here, we report that iron starvation leads to formation of lipids bodies and accumulation of TAGs. This occurs between 12 and 24 h of iron-starvation. C. reinhardtii cells deprived for iron have more saturated FA, due to the loss of functional FA desaturases, which are diiron enzymes. The abundance of a plastid ACP-acyl desaturase (FAB2) is significantly decreased to the same degree as observed for ferredoxin, which is a substrate of the desaturases. The increase in saturated FA (C16:0 and C18:0) is concomitant with the decrease in saturated FA (C16:4, C18:3 or C18:4). This pattern was observed for MGDG, DGTS or DGDG. When we monitored the absolute levels of glycerolipids, MGDG content dropped significantly after only 2 h of iron-starvation. On the other hand, DGTS and DGDG contents gradually decrease until a minimum is reached after 24-48 h of iron-deprivation. RNA-Seq analysis of iron-starved C. reinhardtii cells revealed significant changes in many transcripts coding for enzymes involved in FA metabolism. The mRNA abundances of genes coding for components involved in TAG accumulation (DGAT or MLDP) are increased. A more dramatic increase at the transcript level has been observed for many lipases, suggesting that a major remodeling of lipid membranes occurs during iron-starvation in C. reinhardtii. Overall design: Sampling of Chlamydomonas CC-4532 (2137) cells cultivated photoheterotrophically (TAP) under iron-starvation condition (0 uM Fe-EDTA). Samples were collected from biological duplicates after washing in TAP medium lacking Fe at 0, 0.5, 1, 2, 4, 8, 12, 24 and 48 hours.