Sphingolipids Containing Very-Long-Chain Fatty Acids Define a Secretory Pathway for Specific Polar Plasma Membrane Protein Targeting inArabidopsis 

Abstract

Sphingolipids are a class of structural membrane lipids involved in membrane trafficking and cell polarity. Functional analysis of the ceramide synthase family in Arabidopsis thaliana demonstrates the existence of two activities selective for the length of the acyl chains. Very-long-acyl-chain (C > 18 carbons) but not long-chain sphingolipids are essential for plant development. Reduction of very-long-chain fatty acid sphingolipid levels leads in particular to auxin-dependent inhibition of lateral root emergence that is associated with selective aggregation of the plasma membrane auxin carriers AUX1 and PIN1 in the cytosol. Defective targeting of polar auxin carriers is characterized by specific aggregation of Rab-A2 a -and Rab-A1 elabeled early endosomes along the secretory pathway. These aggregates correlate with the accumulation of membrane structures and vesicle fragmentation in the cytosol. In conclusion, sphingolipids with very long acyl chains define a trafficking pathway with specific endomembrane compartments and polar auxin transport protein cargoes.

Arabidopsis ribosomal proteins control vacuole trafficking and developmental programs through the regulation of lipid metabolism

“…Another mutant, cotyledon vascular pattern 1(cvp1), which is a knock-out mutant of STEROL METHYLTRANSFERASE2 (SMT2), a key enzyme in the sterol biosynthetic pathway, displayed abnormal vascular cell polarity and defectiveness in cell elongation (39,40). The results from ceramide mutants indicate that sphingolipids with very long acyl chains define a trafficking pathway with specific endomembrane compartments and polar auxin transport proteins (25). However, whether those biosynthetic enzymes of lipid pathways are direct targets of auxin regulation or other components are also involved is still not clear.…”

“…However, the molecular mechanism between auxin signaling and vacuole trafficking is still not clear. Intriguingly, lipid metabolism has been linked to auxin regulation with cellular trafficking (24)(25)(26)(27)(28).…”

ATG5 defines a phagophore domain connected to the endoplasmic reticulum during autophagosome formation in plants

“…For correlative microscopy, the grids were placed on a glass slide, GFP signals were collected by confocal microscopy and samples were then post-stained by aqueous 2% uranyl acetate and lead citrate. For complementary ultrastructural studies, the roots were chemically fixed and embedded in LRWhite resin as described 50 . All samples were observed at 120 kV with a JEOL 1400 electron microscope.…”

ORM Expression Alters Sphingolipid Homeostasis and Differentially Affects Ceramide Synthase Activities

“…Recent studies have shown that the Lag1/Lac1 components of the S. cerevisiae ceramide synthase are phosphorylated by Ypk1, and this phosphorylation stimulates ceramide synthase activity in response to heat and reduced intracellular sphingolipid levels (Muir et al, 2014). This finding points to possible coordinated regulation of ORM-mediated SPT and ceramide synthase activities to regulate sphingolipid homeostasis, which is likely more complicated in plants and mammals due to the occurrence of functionally distinct ceramide synthases in these systems (Stiban et al, 2010;Markham et al, 2011;Ternes et al, 2011;Luttgeharm et al, 2016).…”

“…Sphingolipids also are highly enriched in detergent-insoluble membrane fractions of the plasma membrane that form microdomains for proteins with important cell surface activities, including cell wall biosynthesis and hormone transport (Cacas et al, , 2016Perraki et al, 2012;Bayer et al, 2014). In addition, sphingolipids, particularly those with very-long-chain fatty acids (VLCFAs), are integrally associated with Golgi-mediated protein trafficking that underlies processes related to the growth of plant cells (Bach et al, 2008(Bach et al, , 2011Markham et al, 2011;Melser et al, 2011). Furthermore, sphingolipids function through their bioactive long-chain base (LCB) and ceramide metabolites to initiate programmed cell death (PCD), important for mediating plant pathogen resistance through the hypersensitive response (Greenberg et al, 2000;Liang et al, 2003;Shi et al, 2007;Bi et al, 2014;Simanshu et al, 2014).…”