For reasons of simplicity, the major carbon flux necessary to build GDC-0941 mw algal cell walls was ignored in this review, but there should be differences comparing the silicified cell walls of diatoms compared with organic walls of other microalgae [51]. Triacylglycerol

(TAG) is produced from diacylglycerol (DAG) in microalgae through two major routes: the Kennedy Pathway involving transfer of acyl-CoA units onto DAG, catalyzed by diacylglycerol acyltransferase (DGAT), and an acyl-CoA-independent pathway in which acyl groups are transferred from phospholipids, catalyzed by phospholipid:diacylglycerol acyltransferase (PDAT) [52]. Analysis of DGATs showed differences in the number GSK458 mw and types of isoforms present, even within individual algal lineages [53].

Attempts to manipulate DGATs for increased lipid production have had little success [54], suggesting that the acyl-CoA-independent route may deserve more consideration as a contributor than previously thought. Our initial analysis found different numbers of PDAT isoforms between microalgal species, implying that this pathway may be as complex across algal lineages as DGAT and the Kennedy pathway. TAG biosynthesis has long been thought to occur predominantly in the ER, however recently it was shown in Chlamydomonas reinhardtii that a plastid-localized process may contribute HAS1 [ 55 and 56]. Isoprenoid molecules are important precursors for generation of biofuels [57 and 58]. Two major pathways exist for isoprenoid biosynthesis in algae, the cytosolic mevalonate (MVA) pathway using acetyl-CoA, and the plastidic methylerythritolphosphate (MEP) pathway, which is glyeraldehyde-3P and pyruvate dependent [59•]. Chlorophytes have only the MEP pathway, but diatoms additionally have the MVA pathway (Figure 3). The interplay of precursor synthesis and regulation of both pathways is complex with many unknowns [59•]. Specifically important

for metabolic engineering of improved and/or novel biofuels may be carbon partitioning between the isoprenoids and fatty acids. This review highlights the substantial differences in photosynthesis, metabolic networks, and intracellular organization of evolutionarily-distinct classes of microalgae as related to biofuel precursor molecule production. Given the presented examples, one cannot assume that the core carbon metabolism in diverse algal classes will be similar. To facilitate a broadly-informed development of algal biofuels, it will be necessary to use systems biology approaches coupled with biochemical characterization in detailed metabolic studies of examples from the different major algal lineages.