Fig. 4
Schematic representation of the putative enzymatic steps of the glycerolipid metabolism in M. neglectum, including the transcriptional responses to N starvation (stages e−N and l−N) or N resupply (stage r+N). Enzymatic steps are represented by solid arrows and transport processes by dashed lines. For simplicity, PDAT is drawn utilizing PE, but has been shown to also use other lipid substrates [69]. Fatty acid desaturation steps are not shown, except for the generation of oleic acid (C18:1). The localization is drawn according to [8] and for additional reactions according to [87]. Each step has at least one transcript associated, and the putative localization is indicated on the left (C chloroplast, M mitochondrion, O other, S secretory pathway, NA localization prediction not possible due to truncation). The section with the gray Roman numerals next to the predicted localization shows the binned transcript abundance at the reference time point N_0. Five abundance categories are defined: I = below 50% percentile abundance, II = 50–75% percentile abundance, III = 75–90% percentile abundance, IV = 90–99% percentile abundance, V = >99% percentile abundance; see also legend on the bottom right and Fig. 3a for the distribution of FPKM values at N_0. Bold Roman numerals indicate that the respective gene is likely not fragmented, whereas normal font style indicates that only the transcript abundance of the putative fragment containing the 5′ end is shown. The transcription profile of each enzyme is represented by three color boxes, representing the three different cultivation stages investigated in this work (e−N, l−N, r+N). In each of the boxes, the transcriptional regulation at the individual harvesting time points relative to time point zero (N_0) is indicated by color-coded bars (red up-regulation, blue down-regulation compared to N_0). White bars are shown if the change in relative transcript abundance was between 50 and 200% (absolute log2-FC < 1). The tag “NA” (not available) is added if the absolute transcript abundance (as FPKM) at that time point was less than 1.0, which was set as the minimum threshold for reliable transcript abundance estimation. The full annotations of the corresponding genes are given in Additional file 4. ACCase acetyl-CoA carboxylase, ACP acyl carrier protein, ACX acyl-CoA oxidase, AAPT aminoalcoholphosphotransferase (putatively dual substrate specificity producing PC and PE), BTA betaine lipid synthase, CCT CTP:phosphorylcholine cytidylyltransferase, CDS CDP-DAG synthase, CK choline kinase, DGAT diacylglycerol acyltransferase type 1, DGDGS digalactosyldiacylglycerol synthase, DGTT diacylglycerol acyltransferase type 2, ECH multifunctional protein containing a 2E-enoyl-CoA hydratase and a 3S-hydroxyacyl-CoA dehydrogenase, EK ethanolamine kinase, ENR enoyl-ACP reductase, FAT acyl-ACP thioesterase, GPAT glycerol-3-phosphate acyltransferase, HAD hydroxyacyl-ACP dehydrase, KAR ketoacyl-ACP reductase, KAS ketoacyl-ACP synthase, KAT 3-ketoacyl-CoA thiolase, LACS long-chain acyl-CoA synthetase, LPAAT lysophosphatidic acid acyltransferase, LP-C/E-AT lysophosphatidylcholine/ethanolamine acyltransferases, m/c-ACCase mitochondrial or cytosolic ACCase, MCMT malonyl-CoA:acyl carrier protein malonyltransferase, MGDGS monogalactosyldiacylglycerol synthase, MLDP major lipid droplet protein, PAP phosphatidic acid phosphatase, PDAT phospholipid:diacylglycerol acyltransferase, PEAMT phosphoethanolamine N-methyltransferase, PECT CTP:phosphorylethanolamine cytidylyltransferase, PGD1 plastid galactoglycerolipid degradation lipase, PGPP phosphatidylglycerol phosphate, PGPS phosphatidylglycerophosphate synthase, PIS phosphatidylinositol synthase, PSD phosphatidylserine decarboxylase, PSS phosphatidylserine synthase, SAD, Δ9 stearoyl-ACP desaturase, SLS sulfolipid synthase, TE acyl-CoA thioesterase, CDP cytidine diphosphate, CoA coenzyme A, DAG diacylglycerol, DGDG digalactosyldiacylglycerol, DGTS diacylglycerol-N,N,N-trimethylhomoserine, EA ethanolamine, ER endoplasmic reticulum, FA fatty acid, LPE lysophosphatidylethanolamine, MGDG monogalactosyldiacylglycerol, PA phosphatidic acid, PC phosphatidylcholine, PE phosphatidylethanolamine, PGP phosphatidylglycerolphosphate, PG phosphatidylglycerol, PI phosphatidylinositol, SQDG sulfoquinovosyldiacylglycerol, TAG triacylglycerol