Identification of Acyltransferases Associated with Triacylglycerol Biosynthesis in Avocado Fruit

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Modern society’s demand for oil has resulted in depletion of resources and caused higher oil prices. Therefore, natural oil resources of plants are gaining the spotlight and are expected to increase twice that of current use by 2030. Plants are able to accumulate up to 90% oil by dry weight in the form of triacylglycerol (TAG) and it is derived from fleshy part of the fruits, such as mesocarp of oil palm, avocado, and olive. In seed tissues, an acyl CoA-dependent enzyme, diacylglycerol acyltransferase (DGAT) participates in conversion of diacylglycerol (DAG) to TAG. However, TAG can also be formed by an acyl CoA- independent enzyme, phospholipid:diacylglycerol acyltransferase (PDAT). Avocados (Persea americana) store up to ~70% oil in mesocarp and I am interested in identifying the acyltransferase involved in oil biosynthesis in mesocarp tissues. Based on the transcriptome data available, I hypothesize that unlike in seeds, both DGAT and PDAT are associated with TAG biosynthesis in developing mesocarp of avocado. To test this hypothesis, I will determine 1) TAG content and composition and 2) expression levels for DGAT and PDAT genes in mesocarp and seed tissues of five stages of developing fruits of avocado (n=5). Total lipids will be extracted by isopropanol-chloroform method and analyzed for composition as methyl esters on GC-FID. Total RNA, for expression analysis, will be extracted by Trizol method and analyzed with gene-specific primers by real-time PCR. Statistical significance in change in oil content in association with gene expression during fruit development between mesocarp and seed tissues will be analyzed by ANOVA repeated measures. Comparison of temporal gene expression pattern of oil accumulation mesocarp, to that of seed, will allow us to differentiate the acyltransferase(s) specifically associated with TAG biosynthesis. The proposed research work will take the field of plant lipid biochemistry a step forward in understanding TAG synthesis in fruit tissue. Specifically, I will be able to clearly demonstrate the association of a particular acyltransferase to increasing lipid content in a non-seed (mesocarp) tissue. Understanding differences in oil regulation of a basal angiosperm (avocado) in relation to a monocot (oil palm) and a dicot (olive) also will provide additional insights into fundamental changes in TAG biosynthesis during the evolution of flowering plants. My research is part of a global project that includes a group in California, Florida and Israel. Data generated from my proposed work will be used to develop a joint Binational Agricultural and Research proposal. Therefore, my research work will subsequently contribute to development of ways to manipulation of extent and timing of oil accumulationa direct benefit to avocado growers. Furthermore, this study will be a pivotal step to understanding TAG synthesis that will lead to bioenergy crop.


Johnson City, TN

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