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Phosphatidylcholine editing is critical to lipid homeostasis in Arabidopsis trigalactosyldiacylglycerol1 mutants

ABSTRACT: Lipid remodeling is crucial for plant responses to abiotic stress and metabolic disturbances. A key aspect of this process involves the modification of phosphatidylcholine (PC) acyl chains by lysophosphatidylcholine: acyl-CoA acyltransferases (LPCATs). To understand their role in lipid homeostasis, we studied the trigalactosyldiacylglycerol1 (tgd1) mutant, which exhibits significant increases in fatty acid synthesis and flux through PC due to disrupted inter-organelle lipid trafficking. We discovered that the elevated fatty acid synthesis in tgd1 is due to the posttranslational activation of plastidic acetyl-coenzyme A carboxylase (ACCase). Global transcriptomic profiling revealed 62 significantly upregulated genes in tgd1, with 27 (44%) involved in RNA and DNA modifications, suggesting a role for posttranscriptional mechanisms in adapting to lipid trafficking disruptions. Additionally, transcript levels of LPCATs and several genes regulating ACCase were moderately increased in tgd1. Genetic analysis showed that knocking out LPCAT1 and LPCAT2 was lethal in the tgd1 background. Furthermore, plants homozygous for lpcat2 and heterozygous for lpcat1 in the tgd1 background displayed reduced levels of PC and TAG, along with altered fatty acid compositions. Our findings provide mechanistic insights into fatty acid synthesis regulation and highlight the critical role of LPCATs in maintaining cellular lipid homeostasis when fatty acid production exceeds the cellular demand for membrane lipid synthesis.

INSTRUMENT(S): TSQ Altis Plus

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

TISSUE(S): Plant Cell, Seedling

SUBMITTER: Saroj Sah

LAB HEAD: Chancheng Xu

PROVIDER: PXD054661 | Pride | 2024-09-16

REPOSITORIES: Pride

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Project description:Methionine adenosyltransferase (MAT) enzymes generate SAMe (S-adenosylmethionine), the main biological methyl donor. There are two MAT encoding genes in mammals (Mat1a and Mat2a), which show different activities and cellular distribution. Mat1a encodes the enzyme mainly expressed in normal liver. Mat1a ablation in mice results in the spontaneous development of non-alcoholic steatohepatitis (NASH). We observed that SAMe depletion in Mat1a KO mice had three main effects on hepatic lipid metabolism: 1) impaired TG (triglyceride) export via VLDL; 2) impaired mitochondrial FA (fatty acid) oxidation (as evidenced by membrane depolarization, downregulation of Phb1 (prohibitin 1, a mitochondrial chaperone protein) and Mcj/Dnajc15 (endogenous mitochondrial repressor of respiratory chain), and accumulation of long-chain acylcarnitines); and 3) increased FA uptake. The convergence of these three factors induced TG accumulation in LD (lipid droplets). LD expansion confronts hepatocytes with a high demand of PC (phosphatidylcholine) molecules to cover the LD surface since other phospholipids, such as PE (phosphatidylethanolamine), cannot stabilize LD and prevent coalescence. In Mat1a KO this situation is aggravated, since SAMe-dependent PC synthesis via PE methylation is decreased, the PC/PE ratio reduced and mitochondrial FA oxidation impaired. To put a brake to this drain of PC molecules to LD, FA are rerouted in Mat1a KO mice liver to other catabolic (endoplasmic reticulum and peroxisome oxidation) and biosynthetic (ceramides synthesis) pathways, causing oxidative stress, inflammation and fibrosis. SAMe treatment for two months in 8-9 month old Mat1a KO mice ameliorated mitochondrial dysfunction (reduces membrane depolarization, improves Phb1 and Mcj expression, and increases SAMe transport to mitochondria) improving FA oxidation efficiency (FA and acylcarnitine levels decrease), which results in a drastic reduction in TG accumulation. SAMe treatment in Mat1a KO mice resulted in more PC available for proper membrane function, improving liver lipid homeostasis, histology (H&E, Sudan red, Sirius red) and liver injury (ALT, AST).

			Action	DRS
	Peak.xlsx	Xlsx
	TransitionResults.xlsx	Xlsx
	WT_400ng_R1.raw	Raw
	WT_400ng_R2.raw	Raw
	WT_400ng_R3.raw	Raw

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Phosphatidylcholine editing is critical to lipid homeostasis in Arabidopsis trigalactosyldiacylglycerol1 mutants

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