Arabidopsis mutants of sphingolipid fatty acid α‐hydroxylases accumulate ceramides and salicylates

Abstract

SummaryIn Arabidopsis, the fatty acid moiety of sphingolipids is mainly a-hydroxylated. The consequences of a reduction in this modification were analysed.Mutants of both Fatty Acid Hydroxylase genes (AtFAH1 and AtFAH2) were analysed for sphingolipid profiles. To elucidate further consequences of the mutations, metabolic analyses were performed and the influence on pathogen defence was determined.Ceramide and glucosylceramide profiles of double-mutant plants showed a reduction in sphingolipids with a-hydroxylated fatty acid moieties, and an accumulation of sphingolipids without these moieties. In addition, the free trihydroxylated long-chain bases and ceramides were increased by five-and ten-fold, respectively, whereas the amount of glucosylceramides was decreased by 25%. Metabolite analysis of the double mutant revealed salicylates as enriched metabolites. Infection experiments supported the metabolic changes, as the double mutant showed an enhanced disease-resistant phenotype for infection with the obligate biotrophic pathogen Golovinomyces cichoracearum.In summary, these results suggest that fatty acid hydroxylation of ceramides is important for the biosynthesis of complex sphingolipids. Its absence leads to the accumulation of long-chain bases and ceramides as their precursors. This increases salicylate levels and resistance towards obligate biotrophic fungal pathogens, confirming a role of sphingolipids in salicylic aciddependent defence reactions.

Overexpression of BAX INHIBITOR-1 Links Plasma Membrane Microdomain Proteins to Stress

“…The involvement of sphingolipids in plant stress tolerance and cell death regulation is gradually being revealed: an enhanced cell death phenotype was observed in Arabidopsis mutants deficient in ceramide phosphorylation (Greenberg et al, 2000;Liang et al, 2003), sphingosine transfer protein (Brodersen et al, 2002), inositol phosphoceramide biosynthesis (Wang et al, 2008), and the hydroxylation of sphingoid long-chain bases (Chen et al, 2008) and fatty acyl chains (Kӧnig et al, 2012;Nagano et al, 2012). These insights strongly support the importance of sphingolipids in plant stress tolerance and cell death regulation.…”

“…2-HFAs are typical components of the ceramide backbone of sphingolipids (Imai et al, 1995;Pata et al, 2010). Although many functions of plant sphingolipids remain to be elucidated, accumulating evidence clearly indicates that sphingolipids and their metabolism are closely involved in cell death regulation and various stress responses in plants (Ng et al, 2001;Liang et al, 2003;Townley et al, 2005;Chen et al, 2008Chen et al, , 2012Wang et al, 2008;Saucedo-García et al, 2011;Dutilleul et al, 2012;Kӧnig et al, 2012;Nagano et al, 2012;Mortimer et al, 2013), implying that BI-1 plays a role in cell death regulation through sphingolipid metabolism. Sphingolipids are major components of membrane lipids and are at particularly high concentrations in membrane microdomains, known as lipid rafts in animal cells, which are essential for membranemediated signaling and act as a sorting platform for targeted protein traffic (Simons and Toomre, 2000;Staubach and Hanisch, 2011).…”

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

“…This result suggests that PM microdomains produced by OsFAHs participate in the MTI pathway in rice. On the other hand, the salicylic acid (SA) level in OsFAH1/2-KD was similar to that in the wild type (Supplemental Figure 9), although the SA content increased in the Arabidopsis fah1 fah2 mutants described by König et al (2012).…”

“…Both Arabidopsis FAHs (At-FAH1 and At-FAH2) are localized to the endoplasmic reticulum (ER) membrane, and decreasing their levels affects the response to biotic and abiotic stresses (Nagano et al, 2009(Nagano et al, , 2012aKönig et al, 2012). Thus, we hypothesized that FAH could be a useful tool to modify PM microdomains and illuminate the relationship between PM microdomains and innate immunity in plants.…”

Arabidopsis56–Amino Acid Serine Palmitoyltransferase-Interacting Proteins Stimulate Sphingolipid Synthesis, Are Essential, and Affect Mycotoxin Sensitivity

“…Beyond their functions in membranes, sphingolipids, acting through their ceramide and long-chain-base precursors and metabolites, are increasingly regarded as signaling molecules for regulation of a number of physiological processes (Liang et al, 2003;Coursol et al, 2005;Donahue et al, 2010). Ceramide and long-chain-base accumulation has been shown to trigger PCD, which may be important for the hypersensitive response for pathogen defense (Liang et al, 2003;Saucedo-García et al, 2011a;König et al, 2012). 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).…”