Triacylglycerol (TAG) is the main storage lipid in plants, found both in seed and non-seed tissues (e.g. root, leaves, mesocarp etc.). Plants use TAGs as a carbon and energy source during seed germination while humans use plant lipids for biofuel production, industrial feedstocks and nutrition. It is expected that by 2030 the demand for biodiesel will be doubled. To meet this demand it is important to understand the regulation of rate limiting reactions involved in TAG accumulation in nonseed tissues because of their higher biomass relative to the seed tissues. In this study, avocado (Persea americana) is used as a model organism because it is a basal angiosperm and can store up to 70% oil content in the form of TAG in its mesocarp, a nonseed tissue. Typically, the last acylation of diacylglycerol (DAG) to form TAG in seed tissues is catalyzed by diacylglycerol acyltransferases (DGAT) and/or phospholipid:diacylglycerol acyltransferases (PDAT). Based on the transcriptome of avocado, it is hypothesized that both DGAT and PDAT are responsible for catalyzing the terminal step of TAG biosynthesis in mesocarp of avocado. Fulllength coding sequences for DGAT1 and PDAT1 were identified based on the avocado transcriptome data and expressed in TAG-deficient yeast strain (SCY-1998) for complementation. Total lipid extracts from complemented yeast lines will be analyzed for presence of TAG. Furthermore, the enzyme activity and substrate specificity for PaDGAT1 and PaPDAT1 will be determined from microsomal preparations of avocado and eukaryotic expression systems containing the avocado transgenes. This study is expected to identify the enzymes responsible for the terminal acylation step in TAG synthesis in avocado, thereby contributing to the basic understanding of TAG accumulation in nonseed tissues.

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