Abstract
Very long chain fatty acids (VLCFAs) are involved in plant development and particularly in several cellular processes such as membrane trafficking, cell division and cell differentiation. However, the precise role of VLCFAs in these different cellular processes is still poorly understood in plants. In order to identify new factors associated with the biosynthesis or function of VLCFAs, a yeast multicopy suppressor screen was carried out in a yeast mutant strain defective for fatty acid elongation. Loss of function of the elongase 3 hydroxyacyl-CoA dehydratase PHS1 in yeast and PASTICCINO2 in plants prevents growth and induces cytokinesis defects. PROTEIN TYROSIN PHOSPHATASE-LIKE (PTPLA) previously characterized as an inactive dehydratase was able to restore yeast phs1 growth and VLCFAs elongation but not the plant pas2-1 defects. PTPLA interacted with elongase subunits in the Endoplasmic Reticulum (ER) and its absence induced the accumulation of 3-hydroxyacyl-CoA as expected from a dehydratase involved in fatty acid (FA) elongation. However, loss of PTPLA function increased VLCFA levels, an effect that was dependent on the presence of PAS2 indicating that PTPLA activity repressed FA elongation. The two dehydratases have specific expression profiles in the root with PAS2, mostly restricted to the endodermis, while PTPLA was confined in the vascular tissue and pericycle cells. Comparative ectopic expression of PTPLA and PAS2 in their respective domains confirmed the existence of two independent elongase complexes based on PAS2 or PTPLA dehydratase that are functionally interacting.
Highlights
Very long chain fatty acids (VLCFAs) are fatty acids (FA) with an acyl chain longer than 18 carbons
PTPLA was able to restore the growth of the Tet-PHS1 strain in presence of doxycycline (Tet-PHS1+DOX) to levels comparable to Tet-PHS1+DOX strain transformed with PHS1 or PAS2 cDNA albeit the kinetics of growth was slower (Fig 1B)
A similar increase of VLCFA amounts was observed in wild-type R1158 yeast strain expressing PTPLA with more than a two-fold increase that was comparable to the effect of PHS1 and PAS2 expression in wild-type R1158 yeast strain (Fig 1D and S4B Fig)
Summary
Very long chain fatty acids (VLCFAs) are fatty acids (FA) with an acyl chain longer than 18 carbons. They are components of a large variety of plant lipids like the membrane lipids phospholipids and sphingolipids, the storage lipids triacylglycerol and the hydrophobic lipid barrier comprising cuticular waxes and suberin. Fatty Acid Elongation chromatography; KCR, β-Ketoacyl-CoA reductase; KCS, 3-keto-acyl-CoA synthase; LCB, long chain base; NOUR, nourseothricin; PAS, PASTICCINO genes; PCR, polymerase chain reaction; PGK, phosphoglycerate kinase promotor; PHS, phytosphingosine; PHS1, yeast 3-hydroxyacyl-CoA dehydratase; PTPLA, protein tyrosine phosphatase like A; Tet, titrable promoter TetO7; VLCFA, verylong-chain fatty acid. The acyl-CoA elongated by two carbons can re-enter an elongation cycle to eventually produce VLCFAs ranging from C18 to C32 in Arabidopsis
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