Plant sphingolipids: decoding the enigma of the Sphinx

Sphingolipids are a ubiquitous class of lipids present in a variety of organisms including eukaryotes and bacteria. In the last two decades, research has focused on characterizing the individual species of this complex family of lipids, which has led to a new field of research called 'sphingolipidomics'. There are at least 500 (and perhaps thousands of) different molecular species of sphingolipids in cells, and in Arabidopsis alone it has been reported that there are at least 168 different sphingolipids. Plant sphingolipids can be divided into four classes: glycosyl inositol phosphoceramides (GIPCs), glycosylceramides, ceramides, and free long-chain bases (LCBs). Numerous enzymes involved in plant sphingolipid metabolism have now been cloned and characterized, and, in general, there is broad conservation in the way in which sphingolipids are metabolized in animals, yeast and plants. Here, we review the diversity of sphingolipids reported in the literature, some of the recent advances in our understanding of sphingolipid metabolism in plants, and the physiological roles that sphingolipids and sphingolipid metabolites play in plant physiology.