Sphingolipid Δ8 unsaturation is important for glucosylceramide biosynthesis and low‐temperature performance in Arabidopsis

Abstract

SUMMARYPlants contain a large diversity of sphingolipid structures, arising in part from C4 hydroxylation and D4 and D8 desaturation of the component long-chain bases (LCBs). Typically, 85-90% of sphingolipid LCBs in Arabidopsis leaves contain a cis or trans D8 double bond produced by sphingoid LCB D8 desaturase (SLD). To understand the metabolic and physiological significance of D8 unsaturation, studies were performed using mutants of the Arabidopsis SLD genes AtSLD1 and AtSLD2. Our studies revealed that both genes are constitutively expressed, the corresponding polypeptides are ER-localized, and expression of these genes in Saccharomyces cerevisiae yields mixtures of cis/trans D8 desaturation products, predominantly as trans isomers. Consistent in part with the higher expression of AtSLD1 in Arabidopsis plants, AtSLD1 T-DNA mutants showed large reductions in D8 unsaturated LCBs in all organs examined, whereas AtSLD2 mutants showed little change in LCB unsaturation. Double mutants of AtSLD1 and AtSLD2 showed no detectable LCB D8 unsaturation. Comprehensive analysis of sphingolipids in rosettes of these mutants revealed a 50% reduction in glucosylceramide levels and a corresponding increase in glycosylinositolphosphoceramides that were restored by complementation with a wild-type copy of AtSLD1. Double sld1 sld2 mutants lacked apparent growth phenotypes under optimal conditions, but displayed altered responses to certain stresses, including prolonged exposure to low temperatures. These results are consistent with a role for LCB D8 unsaturation in selective channeling of ceramides for the synthesis of complex sphingolipids and the physiological performance of Arabidopsis.

ACYL-LIPID DESATURASE2Is Required for Chilling and Freezing Tolerance inArabidopsis

“…Alternatively, an unidentified ADS2-derived signaling pathway is required to activate some aspects of cold acclimation, which may be important for the development of freezing tolerance. Smith et al (2013) reported that some sphingolipid species are significantly altered in ads2 mutant plants, and its unsaturation has been shown to contribute to cold tolerance in Arabidopsis (Chen et al, 2012), raising the possibility that sphingolipids might play a role in the reduced capacity of cold acclimation in ads2 mutant plants. In addition, since PG is the substrate for cardiolipin biosynthesis in mitochondria, reduced PG content in ads2 mutant plants could result in reduced biosynthesis of cardiolipin, which has also been demonstrated to be essential for optimal mitochondrial function and growth under temperature stress (Jiang et al, 1999;Zhong et al, 2004).…”

Identification of a Sphingolipid α-Glucuronosyltransferase That Is Essential for Pollen Function inArabidopsis

“…Identification of genes encoding sphingolipid biosynthetic proteins has implicated sphingolipids in many important processes including ion transport (Chao et al, 2011), endomembrane trafficking (Markham et al, 2011), programmed cell death (Liang et al, 2003), cold tolerance (Chen et al, 2012), stomatal closure (Coursol et al, 2005), and pollen development (Chen et al, 2006). However, little information is available about the roles of sphingolipid glycosylation.…”

Arabidopsis 56–Amino Acid Serine Palmitoyltransferase-Interacting Proteins Stimulate Sphingolipid Synthesis, Are Essential, and Affect Mycotoxin Sensitivity

“…In plants, sphingolipids are major lipid components of the endomembrane system, plasma membrane, and tonoplast and contribute to membrane physical properties that are important for environmental stress tolerance (Verhoek et al, 1983;Lynch and Steponkus, 1987;Sperling et al, 2005;Chao et al, 2011;Chen et al, 2012). Endomembrane-associated sphingolipids also participate in Golgi-mediated protein trafficking that affects processes such as polar auxin transport (Borner et al, 2005;Aubert et al, 2011;Markham et al, 2011;Yang et al, 2013).…”

“…PCD induction by long-chain-base accumulation appears to be the mode of action for sphinganine analog mycotoxins, including fumonisin B 1 (FB 1 ) and AAL toxin (Abnet et al, 2001;Brandwagt et al, 2002). In addition, phosphorylated forms of long-chain bases (LCBs) have been implicated in abscisic acid-dependent guard cell closure and low temperature signaling in plants (Coursol et al, 2003(Coursol et al, , 2005Chen et al, 2012;Guillas et al, 2013).…”