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  • Exo1 sale Numerous studies have pointed to the DGAT reaction


    Numerous studies have pointed to the DGAT reaction being critical for TAG assembly and in several cases it has been shown to limit carbon flux from lipid precursors towards TAG accumulation [12]. Thus, in Brassica napus, the DGAT substrate, diacylglycerol (DAG), accumulates during periods of rapid lipid formation [15,16]. Moreover, DGAT had the lowest activity (as measured in vitro) in extracts of developing seeds and DAG levels were the highest of all the Kennedy pathway intermediates in seed tissues [17]. In addition, an Arabidopsis thaliana mutant (ASI1) with reduced DGAT activity, had a decreased TAG/DAG ratio compared to wild type plants [18] while Zou et al. showed that this phenotype was due to a mutant allele of the DGAT1 gene [20]. Furthermore, seed-specific over-expression of a DGAT1 gene led to increased oil content in transgenic plants [21]. In B. napus cv. Westar, the Kennedy pathway and associated reactions exerted stronger control over carbon flux to TAG Exo1 sale than did fatty Exo1 sale provision [22]. Also, the overexpression of DGAT1 resulted in lower flux control values for overall TAG assembly [23]. In addition, transgenic B. napus plants with an enhanced DGAT1 activity exhibited increased oil accumulation in field trials [24], again emphasising the importance of DGAT gene expression and enzyme activity for overall oil yields at the level of the crop. Similar studies with other oil-accumulating plants, such as Cuphea, lupin, soybean and Linum species, have supported the notion that DGAT activity is important in determining the overall levels of TAG accumulation [12,25]. In general, the rise in DGAT activity during TAG accumulation parallels that of other Kennedy pathway enzymes [26]. In contrast, activities of enzymes involved in de novo fatty acid biosynthesis do not show such good correlations with oil accumulation [[27], [28], [29]] This suggests that TAG assembly is more tightly controlled than fatty acid synthesis [12]. In the case of E. guineensis, the regulation of TAG synthesis has been studied in detail using callus cultures. The data from control analysis experiments showed that flux control is shared between fatty acid synthesis and TAG assembly [30,31]. In addition, the contribution of DGAT to TAG assembly was assessed directly by inhibition experiments in vitro [32]. Further information about the use of control analysis to give quantitative information about lipid biosynthesis in E. guineensis has been described by Ramli et al. The importance of DGAT in contributing to the regulation of oil accumulation in crops has led to its use, not only in single-gene, over-expressing transgenic lines [21,23,34], but also in plants manipulated for both ‘push’ and ‘pull’ activities. In the former, carbon supply for lipid synthesis is increased (push) while, in the latter, DGAT activity, as the final step in TAG formation, is raised (pull). For example, overexpression of the transcription factor WRI1 (WRINKLED1) and of DGAT1 in tobacco seeds led to enhanced TAG accumulation compared to that expected by an additive effect [35]. Furthermore, a combination of DGAT expression and PGM (phosphoglucomutase) suppression has been used as an example of a combined push/pull strategy to boost TAG yields in the important oil crop, soybean [36,37]. In addition, a combination of DGAT and LEC2 (LEAFY COTYLEDON 2) gene overexpression has been used to increase TAG accumulation in tobacco [38]. The concept of using other enzymes in addition to DGAT in order to raise oil yields has also been used to increase TAG accumulation in tobacco leaves, which do not normally accumulate high levels of TAGs [39]. In this innovative study, carbon flux was increased through both fatty acid synthesis (‘push’) and TAG formation (‘pull’), while at the same time TAG-rich lipid droplets were stabilised via oleosin over-expression (‘package’) and minimising further metabolism by silencing the SDP-1 lipase (‘protect’). This led to an incremental, step-wise increase in the ectopic accumulation of TAG to the remarkably high levels of >30% of leaf dry weight [39].