Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [93]-94).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Not available / text

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [123]-140).

In avocado, an economically important crop, fruits can store up to 70 % oil in the form of triacylglycerols (TAGs). While TAG synthesis in seed tissues mostly depends on an acyl CoA-dependent enzyme, diacylglycerol (DAG) acyltransferase (DGAT) to catalyze the conversion of DAG to TAG, the enzymes involved in non-seed tissues remains to be elucidated. Recent studies on oil palm suggested participation of an acyl-CoA-independent enzyme, phospholipid:diacylglycerol acyltransferase (PDAT), in TAG synthesis. Our research focuses on identifying acyltransferases involved in oil accumulation in mesocarp tissues of avocado. Furthermore, in ‘Hass’ avocado, where 20-60 % of the fruit are phenotypically small, even under favorable conditions, we are interested in determining the association between oil accumulation and fruit size. To this extent, we quantified gene expression levels for DGAT 1 and 2 and PDAT and the rate of oil accumulation in developing mesocarp (oilrich) and seed (non-oil rich) tissues of phenotypically 'small' and 'normal' fruits, using real-time PCR and gas chromatography, respectively. Candidate acyltransferase genes, highly expressed in mesocarp but not in seed, will be cloned and characterized. Understanding TAG synthesis in non-seed tissues will allow us to develop genetic tools necessary for generating bioenergy-rich crops.

No description available.

Triacylglycerol (TAG) is a main storage lipid in seeds and is utilized for seed germination. Humans commonly consume TAG in the form of vegetable oil. Currently, TAG contributes to 25% of the total calories consumed in the developed countries and dependency for biofuel production from plants lipid is also increasing day by day. By 2030 the expected consumption level of vegetable oil will be double and to fulfill this demand it is necessary to increase the oil production in plants. To accomplish this goal, it is pertinent to understand the regulation of TAG accumulation in plants. Avocado (Persea americana), a basal angiosperm, stores up to 70% oil in the form of TAG in nonseed tissue (mesocarp). Here, we use it avocado as a model system to understand TAG biosynthesis in tissues other than seed. In plants, TAG biosynthesis may involve acyl-CoA–dependent or –independent pathway catalyzed by diacylglycerol acyltransferases (DGAT) and phospholipid: diacylglycerol acyltransferases (PDAT), respectively. RNA-Seq and Q-PCR analysis of developing mesocarp of avocado revealed higher expression for DGAT1 and PDAT1, coinciding with the period of TAG accumulation. Therefore, we hypothesize that DGAT1 and PDAT1 are responsible for catalyzing the terminal step in TAG biosynthesis in Avocado mesocarp. Using the transcriptome data, we identified full-length coding sequences for DGAT1 and PDAT1. These acyltransferases are being cloned and will be characterized for their enzyme activity and substrate specificity, subsequent to their expression in yeast. Complementation of Arabidopsis dgat1 and pdat1 mutants and phenotypic characterization will also be carried out using Gateway-cloning techniques and transgenic lines will be assayed for TAG content in seeds. This study is expected to provide basic understanding of TAG accumulation in avocado mesocarp tissue.

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.

N-Acylphosphatidylethanoiamine (NAPE) is synthesized in the microsomes of cotton seedlings by a mechanism that is possibly unique to plants, the ATP-, Ca2+-, and CoA-independent acylation ofphosphatidylethanolamine (PE) with unesterified free fatty acids (FFAs), catalyzed by NAPE synthase. A photoreactive free fatty acid analogue, 12-[(4- azidosalicyl)amino]dodecanoic acid (ASD), and its 125I-labeled derivative acted as substrates for the NAPE synthase enzyme.