Functional Characterization of a Higher Plant Sphingolipid Δ4-Desaturase: Defining the Role of Sphingosine and Sphingosine-1-Phosphate in Arabidopsis

• Published in: Plant physiology (Bethesda) Vol. 149; no. 1; pp. 487 - 498
• Main Authors: Michaelson, Louise V., Zäuner, Simone, Markham, Jonathan E., Haslam, Richard P., Desikan, Radhika, Mugford, Sarah, Albrecht, Sandra, Warnecke, Dirk, Sperling, Petra, Heinz, E., Napier, Johnathan A.
• Format: Journal Article
• Language: English
• Published: American Society of Plant Biologists 2009
• Subjects: Alleles; Biochemical Processes and Macromolecular Structures; Fatty acids; Genes; Guard cells; Lipids; Open reading frames; Plants; Pollen; Polymerase chain reaction; Sphingolipids
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.108.129411

The role of Δ4-unsaturated sphingolipid long-chain bases such as sphingosine was investigated in Arabidopsis (Arabidopsis thaliana). Identification and functional characterization of the sole Arabidopsis ortholog of the sphingolipid Δ4-desaturase was achieved by heterologous expression in Pichia pastoris. A P. pastoris mutant disrupted in the endogenous sphingolipid Δ4-desaturase gene was unable to synthesize glucosylceramides. Synthesis of glucosylceramides was restored by the expression of Arabidopsis gene At4g04930, and these sphingolipids were shown to contain Δ4-unsaturated long-chain bases, confirming that this open reading frame encodes the sphingolipid Δ4-desaturase. At4g04930 has a very restricted expression pattern, transcripts only being detected in pollen and floral tissues. Arabidopsis insertion mutants disrupted in the sphingolipid Δ4-desaturase At4g04930 were isolated and found to be phenotypically normal. Sphingolipidomic profiling of a T-DNA insertion mutant indicated the absence of Δ4-unsaturated sphingolipids in floral tissue, also resulting in the reduced accumulation of glucosylceramides. No difference in the response to drought or water loss was observed between wild-type plants and insertion mutants disrupted in the sphingolipid Δ4-desaturase At4g04930, nor was any difference observed in stomatal closure after treatment with abscisic acid. No differences in pollen viability between wild-type plants and insertion mutants were detected. Based on these observations, it seems unlikely that Δ4-unsaturated sphingolipids and their metabolites such as sphingosine-1-phosphate play a significant role in Arabidopsis growth and development. However, Δ4-unsaturated ceramides may play a previously unrecognized role in the channeling of substrates for the synthesis of glucosylceramides.