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Table 1 List of potential gene targets for genetic engineering approaches to increase lipid production in M. neglectum

From: Time-resolved transcriptome analysis and lipid pathway reconstruction of the oleaginous green microalga Monoraphidium neglectum reveal a model for triacylglycerol and lipid hyperaccumulation

Annotation Locus ID Putative enzyme function Transcript profile Approach Postulated effect References in other microalgae
Acyl-ACP thioesterase (FAT, Fig. 4) XLOC_007529 or XLOC_011123 Cleaves acyl-ACP into a free FA and ACP, thus relieving feedback inhibition of FA synthesis; requires functional interaction with ACP [148] Up-regulated in the l−N stage, down-regulated in the r+N stage Over-expression Deregulation of FA synthesis allowing for total lipid hyperaccumulation under +N conditions [91, 117,118,119,120]
Lipases, such as PGD1 (Fig. 5) XLOC_12515 (PGD1) or XLOC_011377 or XLOC_013518 XLOC_12515: lipase that may act on membrane lipids such as de novo MGDG XLOC_011377: unknown function and no domain predicted; XLOC_013518: unknown function with a predicted patatin_cPLA2 superfamily domain XLOC_12515 and XLOC_011377: both are strongly up-regulated in the l−N stage; expression of XLOC_011377 was highly correlated to MLDP (>0.99) XLOC_013518: abundant transcript; strongly repressed in the l−N stage, and repression was continued during the first 8 h of N resupply Over-expression (XLOC_12515 and XLOC_011377) Knock-down (XLOC_013518) XLOC_12515 and XLOC_011377: membrane lipid turnover putatively triggering TAG accumulation under +N conditions XLOC_01351: might be involved in maintaining membrane lipid integrity; down-regulation could lead to an increased TAG content under +N conditions [73, 121]
Acyl-CoA oxidase (ACX2, Fig. 4) XLOC_015398 Implicated in FA degradation by oxidizing acyl-CoA Up-regulated in the r+N stage Knock-down, deletion Increased TAG content by reducing the rate of FA degradation (repression of catabolic pathways) [31]
Phosphoglycerate kinase (PGK, Fig. 6) XLOC_018937 Converts 3-phosphoglycerate to 1,3-bisphosphoglycerate and vice versa Strongly repressed in the l−N stage, which was continued for the first 4 h in the r+N stage Knock-down Redirecting carbon flow towards pyruvate generation, away from glyceraldehyde-3-phosphate for replenishment of the Calvin cycle NA
PEP carboxylase (PEPC, Fig. 6) XLOC_004101 Carboxylation of PEP to oxalacetate Up-regulated under −N conditions; approximately unaltered transcript levels in the r+N stage Knock-down PEP can be increasingly used for pyruvate generation, rather than for replenishment of the tricarboxylic acid cycle [149,150,151]
Glycerol-3-phosphate dehydrogenase (GPDH, Fig. 6) XLOC_014979 Converts dihydroxyacetone phosphate into glycerol-3-phosphate Up-regulated under −N conditions Over-expression Increased TAG accumulation due to increased supply of glycerol-3-phosphate under −N conditions [106]
Enolase (ENO, Fig. 6) XLOC_012275 Converts 2-phosphoglycerate to PEP Up-regulated under −N conditions Over-expression Possibly altered carbon partitioning towards increased PEP generation under +N conditions [115]
Transcription factor (Additional file 5) XLOC_013389 or XLOC_005581 XLOC_013389: transcription factor of MYB family XLOC_005581: transcription factor of GATA family XLOC_013389: strongly up-regulated under –N conditions; XLOC_005581: strongly repressed under –N conditions Over-expression (XLOC_013389), knock-down (XLOC_005581) Mimicking parts of the transcriptional regulation from −N conditions under +N conditions [125, 126]
Small subunit of RuBisCo (rbcS2) or elongation factor or ribosomal protein (RPL7aE) (Additional file 1: Figure S2b) XLOC_007679 or XLOC_005939 or XLOC_000987 XLOC_007679: rbcS2, central enzyme of photosynthesis catalyzing carbon fixation XLOC_005939 and XLOC_000987: implicated in protein biosynthesis XLOC_007679: the third highest rate of expression under +N conditions, and only moderately affected by the −N treatment; the first intron could putatively contain an enhancer motif as in [152] XLOC_005939 and XLOC_000987: very high and stable expression under −N conditions Cloning Strong constitutive promoter for both +N and −N conditions [152, 153]
  1. The table is sorted according to pathways, starting with the glycerolipid metabolism, followed by the central carbon metabolism, finishing with other targets