title: Recruiting a new substrate for triacylglycerol synthesis in plants: the monoacylglycerol acyltransferase pathway.
abstract: BACKGROUND
  Monoacylglycerol acyltransferases (MGATs) are predominantly associated with lipid absorption and resynthesis in the animal intestine where they catalyse the first step in the monoacylglycerol (MAG) pathway by acylating MAG to form diacylglycerol (DAG). Typical plant triacylglycerol (TAG) biosynthesis routes such as the Kennedy pathway do not include an MGAT step. Rather, DAG and TAG are synthesised de novo from glycerol-3-phosphate (G-3-P) by a series of three subsequent acylation reactions although a complex interplay with membrane lipids exists.
  
  
  RESULTS
  We demonstrate that heterologous expression of a mouse MGAT acyltransferase in Nicotiana benthamiana significantly increases TAG accumulation in vegetative tissues despite the low levels of endogenous MAG substrate available. In addition, DAG produced by this acyltransferase can serve as a substrate for both native and coexpressed diacylglycerol acyltransferases (DGAT). Finally, we show that the Arabidopsis thaliana GPAT4 acyltransferase can produce MAG in Saccharomyces cerevisiae using oleoyl-CoA as the acyl-donor.
  
  
  CONCLUSIONS
  This study demonstrates the concept of a new method of increasing oil content in vegetative tissues by using MAG as a substrate for TAG biosynthesis. Based on in vitro yeast assays and expression results in N. benthamiana, we propose that co-expression of a MAG synthesising enzyme such as A. thaliana GPAT4 and a MGAT or bifunctional M/DGAT can result in DAG and TAG synthesis from G-3-P via a route that is independent and complementary to the endogenous Kennedy pathway and other TAG synthesis routes.
authors.affiliation: CSIRO Food Futures National Research Flagship, Canberra, ACT, Australia.
authors.forename: James R
authors.initials: JR
authors.lastname: Petrie
authors.forename: Thomas
authors.initials: T
authors.lastname: Vanhercke
authors.forename: Pushkar
authors.initials: P
authors.lastname: Shrestha
authors.forename: Anna
authors.initials: A
authors.lastname: El Tahchy
authors.forename: Adam
authors.initials: A
authors.lastname: White
authors.forename: Xue-Rong
authors.initials: XR
authors.lastname: Zhou
authors.forename: Qing
authors.initials: Q
authors.lastname: Liu
authors.forename: Maged P
authors.initials: MP
authors.lastname: Mansour
authors.forename: Peter D
authors.initials: PD
authors.lastname: Nichols
authors.forename: Surinder P
authors.initials: SP
authors.lastname: Singh
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism; D051048:Diacylglycerol O-Acyltransferase / Q000378:metabolism; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000378:metabolism; D005994:Glycerophosphates / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D051379:Mice; D050178:Monoglycerides / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D014026:Nicotiana / Q000201:enzymology; D014280:Triglycerides / Q000096:biosynthesis*
chemical_list: D005994:Glycerophosphates; D050178:Monoglycerides; D014280:Triglycerides; D000217:Acyltransferases; D005992:Glycerol-3-Phosphate O-Acyltransferase; D051048:Diacylglycerol O-Acyltransferase; C021802:2-acylglycerol O-acyltransferase