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BMC Plant Biol. 2012; 12: 4.
Published online Jan 10, 2012. doi:  10.1186/1471-2229-12-4
PMCID: PMC3310826
Triacylglycerol synthesis by PDAT1 in the absence of DGAT1 activity is dependent on re-acylation of LPC by LPCAT2
Jingyu Xu,1 Anders S Carlsson,2 Tammy Francis,1 Meng Zhang,3 Travis Hoffman,1 Michael E Giblin,1 and David C Taylorcorresponding author1,4
1National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, SK S7N 0W9, Canada
2Plant Breeding and Biotechnology, Swedish University of Agricultural Sciences, Box 101, Sundsvägen 14, 230 53 Alnarp, Sweden
3College of Agronomy, Northwest A & F University, No.3 Taicheng Road, Yangling, Shanxi 712100, China
4NRC Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, SK S7N 0W9, Canada
corresponding authorCorresponding author.
Jingyu Xu: Jingyu.Xu/at/nrc-cnrc.gc.ca; Anders S Carlsson: Anders.Carlsson/at/slu.se; Tammy Francis: Tammy.Francis/at/nrc-cnrc.gc.ca; Meng Zhang: zhangm/at/nwsuaf.edu.cn; Travis Hoffman: Travis.Hoffman/at/nrc-cnrc.gc.ca; Michael E Giblin: Mike.Giblin/at/nrc-cnrc.gc.ca; David C Taylor: David.Taylor/at/nrc-cnrc.gc.ca
Received July 21, 2011; Accepted January 10, 2012.
Abstract
Background
The Arabidopsis thaliana dgat1 mutant, AS11, 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, AS11 still manages to make 70% of WT seed oil levels. Recently, it was demonstrated that in the absence of DGAT1, PDAT1 was essential for normal seed development, and is a dominant determinant in Arabidopsis TAG biosynthesis.
Methods
Biochemical, metabolic and gene expression studies combined with genetic crossing of selected Arabidopsis mutants have been carried out to demonstrate the contribution of Arabidopsis PDAT1 and LPCAT2 in the absence of DGAT1 activity.
Results
Through microarray and RT-PCR gene expression analyses of AS11 vs. WT mid-developing siliques, we observed consistent trends between the two methods. FAD2 and FAD3 were up-regulated and FAE1 down-regulated, consistent with the AS11 acyl phenotype. PDAT1 expression was up-regulated by ca 65% while PDAT2 expression was up-regulated only 15%, reinforcing the dominant role of PDAT1 in AS11 TAG biosynthesis. The expression of LPCAT2 was up-regulated by 50-75%, while LPCAT1 expression was not significantly affected. In vitro LPCAT activity was enhanced by 75-125% in microsomal protein preparations from mid-developing AS11 seed vs WT. Co-incident homozygous knockout lines of dgat1/lpcat2 exhibited severe penalties on TAG biosynthesis, delayed plant development and seed set, even with a functional PDAT1; the double mutant dgat1/lpcat1 showed only marginally lower oil content than AS11.
Conclusions
Collectively, the data strongly support that in AS11 it is LPCAT2 up-regulation which is primarily responsible for assisting in PDAT1-catalyzed TAG biosynthesis, maintaining a supply of PC as co-substrate to transfer sn-2 moieties to the sn-3 position of the enlarged AS11 DAG pool.
Keywords: dgat1 mutant AS11, LPCAT1, LPCAT2, PDAT1, Oil biosynthesis Seed lines from Nottingham Arabidopsis Stock Centre WT (ecotype Columbia-0); dgat1, AS11 (CS3861); A7 (SALK_039456); lpcat1 (SALK_123480); lpcat2 (SAIL_357_H01) (all in a Columbia background)
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