Disruption of the ceramide synthase LOH1 causes spontaneous cell death inArabidopsis thaliana

Abstract

Summary• The bioactive lipid ceramide is produced by the enzyme ceramide synthase, which exists in several isoforms in most eukaryotic organisms. Here, we investigated functional differences between the three ceramide synthase isoforms in Arabidopsis thaliana.• The biochemical properties of the three ceramide synthases were investigated by comparing lipid profiles of yeast strains expressing LOH1, LOH2 or LOH3 with those of wild-type and loh1, loh2 and loh3 knockout plants. Expression profiles of the ceramide synthases and of the pathogenesis-related gene PR-1 were investigated by real-time PCR.• Each ceramide synthase isoform showed a characteristic preference regarding acyl-CoA chain length as well as sphingoid base hydroxylation, which matches the pattern of ceramide and glucosylceramide species found in leaves. After extended culture under short-day conditions, loh1 plants showed spontaneous cell death accompanied by enhanced expression of PR-1. The levels of free trihydroxy sphingoid bases as well as ceramide and glucosylceramide species with C 16 fatty acid were significantly elevated while species with C 20 -C 28 fatty acids were reduced.• These data suggest that spontaneous cell death in the loh1 line is triggered either by the accumulation of free trihydroxy sphingoid bases or ceramide species with C 16 fatty acid.

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).…”

“…Class I ceramide synthase activity resulting from the Longevity Assurance Gene One Homolog2 (LOH2)-encoded ceramide synthase acylates, almost exclusively, LCBs containing two hydroxyl groups (dihydroxy LCBs) with 16:0-CoA to form C16 ceramides, which are used primarily for GlcCer synthesis Ternes et al, 2011;Luttgeharm et al, 2016). Class II ceramide synthase activities resulting from the LOH1-and LOH3-encoded ceramide synthases are most active in the acylation of LCBs containing three hydroxyl groups (trihydroxy LCBs) with VLCFA-CoAs, including primarily C 24 and C 26 acyl-CoAs Ternes et al, 2011;Luttgeharm et al, 2016). Class II (LOH1 and LOH3) ceramide synthase activity is essential for producing VLCFA-containing glycosphingolipids to support the growth of plant cells, whereas class I (LOH2) ceramide synthase activity is nonessential under normal growth conditions Luttgeharm et al, 2015b).…”

“…Two functionally distinct classes of ceramide synthases occur in Arabidopsis, designated class I and class II . Class I ceramide synthase activity resulting from the Longevity Assurance Gene One Homolog2 (LOH2)-encoded ceramide synthase acylates, almost exclusively, LCBs containing two hydroxyl groups (dihydroxy LCBs) with 16:0-CoA to form C16 ceramides, which are used primarily for GlcCer synthesis Ternes et al, 2011;Luttgeharm et al, 2016). Class II ceramide synthase activities resulting from the LOH1-and LOH3-encoded ceramide synthases are most active in the acylation of LCBs containing three hydroxyl groups (trihydroxy LCBs) with VLCFA-CoAs, including primarily C 24 and C 26 acyl-CoAs Ternes et al, 2011;Luttgeharm et al, 2016).…”

Plasma Membrane Microdomains Are Essential for Rac1-RbohB/H-Mediated Immunity in Rice

“…SA was prepared using MTBE/methanol/water and quantified by LC-MS/ MS according to Ternes et al (2011).…”

Possible Role of Sphingolipids in Developmental Programmed Cell Death of Petunia Petals

“…The major plant sphingolipids typically contain a C18 aliphatic amino alcohol chain (also called sphingoid long-chain base). The aliphatic amino alcohol chain can be dihydroxylated (d) or trihydroxylated (t) [16,17]. Plant sphingolipids have a fatty acid chain of various lengths (about C14 to C28), but the preponderance of plant sphingolipids has a C16 fatty acid chain [18,19].…”