Abstract
Phosphatidylserine (PS) decarboxylase is involved in the synthesis of the abundant phospholipid phosphatidylethanolamine (PE), particularly in mitochondria, in many organisms, including yeast (Saccharomyces cerevisiae) and animals. Arabidopsis (Arabidopsis thaliana) contains three genes with sequence similarity to PS decarboxylases, and the respective gene products were functionally characterized after heterologous expression in yeast and Escherichia coli. While the PSD1 protein localizes to mitochondria, PSD2 and PSD3 are found in the endomembrane system. To study the role of PSD genes in plant phospholipid metabolism, Arabidopsis insertional mutants for psd1, psd2, and psd3 were obtained. The single mutants were decreased in PS decarboxylase activity to various extents, but mutant plants showed no obvious growth or morphological phenotype. A triple mutant, psd1 psd2 psd3, was generated that was totally devoid of PS decarboxylase activity. While the phospholipid composition in whole leaves was unchanged, the PE content in isolated mitochondria of psd1 psd2 psd3 was decreased. Therefore, the predominant proportion of PE in Arabidopsis is synthesized by alternative pathways, but a significant amount of mitochondrial PE is derived from the PS decarboxylase reaction. These results imply that, similar to yeast and animal cells, a specific phospholipid transfer from the endoplasmic reticulum to mitochondria exists in plants.
Highlights
Phosphatidylserine (PS) decarboxylase is involved in the synthesis of the abundant phospholipid phosphatidylethanolamine (PE), in mitochondria, in many organisms, including yeast (Saccharomyces cerevisiae) and animals
Phospholipid metabolism in plants involves a complex network of biosynthetic pathways, some of which are localized to different subcellular compartments
Mitochondrial PS decarboxylase is involved in the synthesis of a major proportion of cellular PE
Summary
Phosphatidylserine (PS) decarboxylase is involved in the synthesis of the abundant phospholipid phosphatidylethanolamine (PE), in mitochondria, in many organisms, including yeast (Saccharomyces cerevisiae) and animals. The predominant proportion of PE in Arabidopsis is synthesized by alternative pathways, but a significant amount of mitochondrial PE is derived from the PS decarboxylase reaction These results imply that, similar to yeast and animal cells, a specific phospholipid transfer from the endoplasmic reticulum to mitochondria exists in plants. At least three different pathways contribute to the synthesis of PE in spinach leaves, i.e. decarboxylation of PS (PS decarboxylase), phosphoethanolamine transfer from CDP-ethanolamine to diacylglycerol (aminoalcoholphospho-transferase; Kennedy/nucleotide pathway), and exchange of the head group of PE with Ser (base exchange enzyme; Marshall and Kates, 1973). Other plant species, such as Arabidopsis, do not contain genes with sequence similarity to wheat PS synthase, and, plants seem to employ distinct routs for PS production
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