Sphingosine in plants – more riddles from the Sphinx?

Summary •Sphingolipids are emerging as important mediators of cellular and developmental processes in plants, and advances in lipidomics have yielded a wealth of information on the composition of plant sphingolipidomes. Studies using Arabidopsis thaliana showed that the dihydroxy long-chain base (LCB) is desaturated at carbon position 8 (d18:1Δ8). This raised important questions on the role(s) of sphingosine (d18:1Δ4) and sphingosine-1-phosphate (d18:1Δ4-P) in plants, as these LCBs appear to be absent in A. thaliana. •Here, we surveyed 21 species from various phylogenetic groups to ascertain the position of desaturation of the d18:1 LCB, in order to gain further insights into the prevalence of d18:1Δ4 and d18:1Δ8 in plants. •Our results showed that d18:1Δ8 is common in gymnosperms, whereas d18:1Δ4 is widespread within nonseed land plants and the Poales, suggesting that d18:1Δ4 is evolutionarily more ancient than d18:1Δ8 in Viridiplantae. Additionally, phylogenetic analysis indicated that the sphingolipid Δ4-desaturases from Viridiplantae form a monophyletic group, with Angiosperm sequences falling into two distinct clades, the Eudicots and the Poales. •We propose that efforts to elucidate the role(s) of d18:1Δ4 and d18:1Δ4-P should focus on genetically tractable Viridiplantae species where the d18:1 LCB is desaturated at carbon position 4.