Among the various fuel categories derived from microalgae, biodiesel receives the most attention because it shares similar chemical characteristics with petrol diesel and can be directly channeled into the current transportation infrastructure without major alterations of existing technology and fuel pipelines. Oleaginous green microalgae species that have the capacity to accumulate oil in the form of triacylglycerols, or TAGs (Chisti, 2007; Sheehan et al., 1998), have been isolated and possess great potential as a feedstock for biodiesel fuels (Converti et al., 2009; Liu et al., 2008; Xu et al., 2006). However, microalgae-based biodiesel is far from being commercially feasible, because it is not economically practical at present. From a biological point of view, one of the obvious solutions is to increase oil content. Most microalgae do not accumulate large amounts of lipid during a normal growth period. Cells begin to accumulate significant amounts of storage lipids after encountering stress conditions such as light and nutrient starvation (Hu et al., 2008; Sheehan et al., 1998). Nutrient starvation, however, slows cell proliferation and therefore limits biomass and overall lipid productivity. Despite the continuous interest in and enthusiasm about microalgal oil-to-biodiesel potential, the molecular mechanisms underlying the cellular, physiological, and metabolic networks connecting to lipid and TAG biosynthesis remain largely unknown. Recent progress in transcriptomics, proteomics, metabolomics, and lipidomics studies have started to unravel the complex molecular mechanisms and regulatory networks involved in lipid and TAG biosynthesis in microalgae.

Current efforts to isolate and characterize the repertoire of genes required for lipid and TAG biosynthesis and accumulation in microalgae have focused on a model microalga: Chlamydomonas reinhardtii (Li et al., 2008; Miller et al., 2010; Msanne et al., 2012). With com­plete genome information, many enzymes required for lipid and TAG biosynthesis and me­tabolism have been identified based on in silico predictions of orthologous genes from other organisms (Riekhof et al., 2005). Similar to oilseed crops, the most common fatty acids in microalgae are 16- and 18-carbon fatty acids (Hu et al., 2008). Genome comparison and gene prediction analyses have shown that the pathways of fatty acid and lipid biosynthesis are largely conserved between plants and green algae (Riekhof et al., 2005). In plants, de novo syn­thesis of fatty acids occurs in the plastid (Ohlrogge and Browse, 1995). The synthesized fatty acids are used as building blocks for synthesis of membrane lipids and storage lipids. Acetyl CoA serves as the basic unit for fatty acid biosynthesis. It is converted to malonyl CoA by acetyl