| Summary: | <p>Abstract</p> <p>Background</p> <p>The <it>Arabidopsis thaliana dgat1 </it>mutant, <it>AS11</it>, has an oil content which is decreased by 30%, and a strongly increased ratio of 18:3/20:1, compared to wild type. Despite lacking a functional DGAT1, <it>AS11 </it>still manages to make 70% of WT seed oil levels. Recently, it was demonstrated that in the absence of <it>DGAT1</it>, <it>PDAT1 </it>was essential for normal seed development, and is a dominant determinant in <it>Arabidopsis </it>TAG biosynthesis.</p> <p>Methods</p> <p>Biochemical, metabolic and gene expression studies combined with genetic crossing of selected <it>Arabidopsis </it>mutants have been carried out to demonstrate the contribution of <it>Arabidopsis </it>PDAT1 and LPCAT2 in the absence of DGAT1 activity.</p> <p>Results</p> <p>Through microarray and RT-PCR gene expression analyses of <it>AS11 </it>vs. WT mid-developing siliques, we observed consistent trends between the two methods. <it>FAD2 </it>and <it>FAD3 </it>were up-regulated and <it>FAE1 </it>down-regulated, consistent with the <it>AS11 </it>acyl phenotype. <it>PDAT1 </it>expression was up-regulated by <it>ca </it>65% while <it>PDAT2 </it>expression was up-regulated only 15%, reinforcing the dominant role of <it>PDAT1 </it>in <it>AS11 </it>TAG biosynthesis. The expression of <it>LPCAT2 </it>was up-regulated by 50-75%, while <it>LPCAT1 </it>expression was not significantly affected. <it>In vitro </it>LPCAT activity was enhanced by 75-125% in microsomal protein preparations from mid-developing <it>AS11 </it>seed <it>vs </it>WT. Co-incident homozygous knockout lines of <it>dgat1</it>/<it>lpcat2 </it>exhibited severe penalties on TAG biosynthesis, delayed plant development and seed set, even with a functional PDAT1; the double mutant <it>dgat1/lpcat1 </it>showed only marginally lower oil content than <it>AS11</it>.</p> <p>Conclusions</p> <p>Collectively, the data strongly support that in <it>AS11 </it>it is <it>LPCAT2 </it>up-regulation which is primarily responsible for assisting in PDAT1-catalyzed TAG biosynthesis, maintaining a supply of PC as co-substrate to transfer <it>sn</it>-2 moieties to the <it>sn</it>-3 position of the enlarged <it>AS11 </it>DAG pool.</p>
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