Every cell is capable of synthesizing and storing triacylglycerols (TAGs) as carbon and/or energy source. Although the biosynthetic pathways that lead to formation of TAG are well established, knowledge on the factors that determine the amount of TAG to be synthesized in a cell is still scarce. Thus, the overall aim of this thesis is to analyze the role of sub- or micro-domains of the ER and lipid droplets (LD) in TAG formation and to use the gained knowledge to achieve an increase in the TAG content in plants and algae. The flowering plant Arabidopsis thaliana and the monocellular microalgae Phaeodactylum tricornutum will serve as model organisms for this study and two different homologs of Arabidopsis acyl-CoA:diacylglycerol acyltransferases DGAT1+ 3), the key-enzyme of the TAG-synthesis, are targets to influence the TAG accumulation in these organisms. The central hypothesis that will be tested is the assumption that the flux into TAG biosynthesis can be increased by reallocating its central steps in artificial micro-domains either at the ER or directly to LDs. Therefore, different combinations of enzymes were overexpressed as fusion proteins with oleosin that targets these proteins to the LD membrane. The functionality of the fusion proteins was confirmed via expression in appropriate yeast mutants. Finally TAG accumulation was tested in seeds and P. tricornutum. weiterlesen