Modification of seed oil content and acyl composition in the brassicaceae by expression of a yeast sn-2 acyltransferase gene.

Abstract

A putative yeast sn-2 acyltransferase gene (SLC7-7), reportedly a variant acyltransferase that suppresses a genetic defect in sphingolipid long-chain base biosynthesis, has been expressed in a yeast SLC deletion strain. The SLC7-7 gene product was shown in vitro to encode an sn-2 acyltransferase capable of acylating sn-1 oleoyl-lysophosphatidic acid, using a range of acyl-COA thioesters, including 181-, 22:l-, and 240-COAS. The SLC7-7 gene was introduced into Arabidopsis and a high erucic acid-containing Brassica napus cv Hero under the control of a constitutive (tandem cauliflower mosaic virus 35s) promoter. The resulting transgenic plants showed substantial increases of 8 to 48% in seed oil content (expressed on the basis of seed dry weight) and increases in both overall proportions and amounts of very-long-chain fatty acids in seed triacylglycerols (TAGs). Furthermore, the proportion of very-long-chain fatty acids found at the sn-2 position of TAGs was increased, and homogenates prepared from developing seeds of transformed plants exhibited elevated lysophosphatidic acid acyltransferase (EC 2.3.1 51) activity. Thus, the yeast sn-2 acyltransferase has been shown to encode a protein that can exhibit lysophosphatidic acid acyltransferase activity and that can be used to change total fatty acid content and composition as well as to alter the stereospecific acyl distribution of fatty acids in seed TAGS.

Erucic acid rapeseed: 1. Prospects of improvements

“…These findings, as well as the increase in the oil content, highlight the effect of the yeast LPAAT which allows an increase in the flow of fatty acids in the triglycerides biosynthetic pathway. The use of acyl-CoA thioesters by all acyltransferases involved in the biosynthesis of triglycerides seems to stimulate the biosynthesis of VLCFAs probably by removing feedback inhibition (Frentzen, 1998;Zou et al, 1997). The results obtained with the yeast LPAAT should be attributed to the specific properties of this enzyme.…”

“…However, the overall proportions of 22:1 in the seed oil did not increase. Zou et al (1997) have confirmed that the yeast (Saccharomyces cerevisiae) SLC1-1 gene encodes sn-2-acyltransferase capable of acylating sn-1-oleoyl-lysophosphatidic acid using a range of acyl-CoA thioesters, including 22:1-CoA. However, neither the meadowfoam nor the yeast-LPAAT transgene approach was successful in achieving high trierucin content in HEAR B. napus seed oil.…”

“…Although class B LPAATs have been exploited to alter the stereochemical composition of rapeseed (Brassica napus) oil to permit the incorporation of modified fatty acids at sn-2 (Knutzon et al, 1999;Lassner et al, 1995), a significant increase in the total amount of unusual fatty acid was not accomplished by the expression of the class B LPAATs alone. In contrast, the transformation of rapeseed and Arabidopsis thaliana with a yeast gene encoding a variant LPAAT, SLC1-1, capable of accepting very long chain fatty acyl (VLCFA)-CoA substrates resulted in an increase in the total VLCFAs and, unexpectedly, in total oil content (Zou et al, 1997).…”

“…Finally, new perspectives have been provided by Zou's team (Frentzen, 1998;Zou et al, 1997). They developed transgenic rapeseed with high erucic acid content expressing a variant LPAAT yeast (Saccharomyces cerevisiae), encoded by the gene SLC1-1 (Frentzen, 1998;Nagiec et al, 1993), which can use a wide range of acyl-CoA thioesters with long and very long chains and also seems to have low specificity for acyl acceptors (Frentzen, 1998;Zou et al, 1997).…”

“…They developed transgenic rapeseed with high erucic acid content expressing a variant LPAAT yeast (Saccharomyces cerevisiae), encoded by the gene SLC1-1 (Frentzen, 1998;Nagiec et al, 1993), which can use a wide range of acyl-CoA thioesters with long and very long chains and also seems to have low specificity for acyl acceptors (Frentzen, 1998;Zou et al, 1997). However, it appears that the expression of the LPAAT from yeast does not only affect the stereochemical composition of the oil of the transgenic plants, but also the proportions of C22:1 and oil.…”