Diacylglycerol acyltransferases (DGATs) catalyse the final step of the triacylglycerol (TAG) biosynthesis of the Kennedy pathway. Two major gene families have been shown to encode DGATs, DGAT1 (type-1) and DGAT2 (type-2). Both genes encode membrane-bound proteins, with no sequence homology to each other. In this study, the molecular cloning and characterization of a type-2 DGAT cDNA from olive is presented. Southern blot analysis showed that OeDGAT2 is represented by a single copy in the olive genome. Comparative transcriptional analysis revealed that DGAT1 and DGAT2 are developmentally regulated and share an overall overlapping but distinct transcription pattern in various tissues during vegetative growth. DGAT2 is highly expressed in mature or senescing olive tissues. In flowers, the expression of DGAT1 was almost undetectable, while DGAT2 transcripts accumulated at the later stages of both anther and ovary development. Differential gene regulation was also detected in the seed and mesocarp, two drupe compartments that largely differ in their functional roles and mode of lipid accumulation. DGAT1 appears to contribute for most of the TAG deposition in seeds, whereas, in the mesocarp, both DGAT1 and DGAT2 share an overlapping expression pattern. During the last stages of mesocarp growth, when TAGs are still accumulating, strong up-regulation of DGAT2 but a marked decline of DGAT1 transcript levels were detected. The present results show overlapping gene expression for olive DGATs during mesocarp growth, with a more prominent implication of DGAT2 in floral bud development and fruit ripening.
The relative abundance of alpha-linolenic (alpha-LeA) compared with linoleic acid is associated with the developmental stage and the plant species and is proposed to have important physiological effects on both vegetative and reproductive plant development. The enzymes responsible for catalyzing the conversion of linoleic acid to alpha-LeA, the omega-3 fatty acid desaturases (FADs), are localized in the plastid or the endoplasmic reticulum (ER). Here we present the isolation of an ER-type omega-3 FAD gene (OeFAD3) from olive (Olea europaea L.). Expression patterns of OeFAD3 in different seed tissues and mesocarps during olive fruit development showed that its contribution to olive oil biosynthesis and modification is minimal. Regulation of OeFAD3 differed from that of its plastidial counterpart, being preferentially expressed in proliferating tissues, in concert with the active membrane biogenesis required for cell division. Trienoic acid-deficient Arabidopsis mutants are male sterile, because alpha-LeA-derived jasmonic acid (JA) is required for pollen development. However, the upregulation of OeFAD3 in different pistil tissues, particularly in vascular bundles and ovaries, rather than in anthers, implies a critical role of alpha-LeA in female gametophyte development in olive, corroborating results from JA-defective tomato mutants that are female sterile but not male sterile.
The carob snack led to increased satiety, lower energy intake at meal, and decreased postmeal glycemic response possibly due to its low GI value. Identifying foods that promote satiety and decrease glycemic response without increasing the overall energy intake may offer advantages to body weight and glycemic control.
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