title: Fatty acid synthesis is inhibited by inefficient utilization of unusual fatty acids for glycerolipid assembly.
abstract: Degradation of unusual fatty acids through β-oxidation within transgenic plants has long been hypothesized as a major factor limiting the production of industrially useful unusual fatty acids in seed oils. Arabidopsis seeds expressing the castor fatty acid hydroxylase accumulate hydroxylated fatty acids up to 17% of total fatty acids in seed triacylglycerols; however, total seed oil is also reduced up to 50%. Investigations into the cause of the reduced oil phenotype through in vivo [(14)C]acetate and [(3)H]2O metabolic labeling of developing seeds surprisingly revealed that the rate of de novo fatty acid synthesis within the transgenic seeds was approximately half that of control seeds. RNAseq analysis indicated no changes in expression of fatty acid synthesis genes in hydroxylase-expressing plants. However, differential [(14)C]acetate and [(14)C]malonate metabolic labeling of hydroxylase-expressing seeds indicated the in vivo acetyl-CoA carboxylase activity was reduced to approximately half that of control seeds. Therefore, the reduction of oil content in the transgenic seeds is consistent with reduced de novo fatty acid synthesis in the plastid rather than fatty acid degradation. Intriguingly, the coexpression of triacylglycerol synthesis isozymes from castor along with the fatty acid hydroxylase alleviated the reduced acetyl-CoA carboxylase activity, restored the rate of fatty acid synthesis, and the accumulation of seed oil was substantially recovered. Together these results suggest a previously unidentified mechanism that detects inefficient utilization of unusual fatty acids within the endoplasmic reticulum and activates an endogenous pathway for posttranslational reduction of fatty acid synthesis within the plastid.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS 39402.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Bates
authors.forename: Sean R
authors.initials: SR
authors.lastname: Johnson
authors.forename: Xia
authors.initials: X
authors.lastname: Cao
authors.forename: Jia
authors.initials: J
authors.lastname: Li
authors.forename: Jeong-Won
authors.initials: JW
authors.lastname: Nam
authors.forename: Jan G
authors.initials: JG
authors.lastname: Jaworski
authors.forename: John B
authors.initials: JB
authors.lastname: Ohlrogge
authors.forename: John
authors.initials: J
authors.lastname: Browse
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D017360:Arabidopsis / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005227:Fatty Acids / Q000096:biosynthesis*; D025461:Feedback, Physiological; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D008055:Lipids / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010938:Plant Oils / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012313:RNA / Q000378:metabolism; D012639:Seeds / Q000378:metabolism; D013997:Time Factors; D019076:Transgenes; D014280:Triglycerides / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D008055:Lipids; D010938:Plant Oils; D014280:Triglycerides; D012313:RNA; D000103:Acetyl-CoA Carboxylase; D010100:Oxygen
keywords: feedback inhibition; metabolic engineering; β-oxidation