Lipid signaling in Arabidopsis: no sphingosine? No problem!

The evidence for sphingosine-1-phosphate (S1P) as a signaling molecule in mammals has been extended to plants, where it is implicated in abscisic acid (ABA)-mediated stomatal closure. However, a recent description of sphingosine- and S1P-deficient mutants of Arabidopsis thaliana provides evidence against a unique role for S1P in ABA signaling in plants because guard cell behavior in response to ABA is unaffected in these mutants. These results and other recent publications indicate that other long-chain base-1-phosphates participate in ABA signaling in plants. As we discuss here, these findings also highlight the need for recognizing the large structural heterogeneity of plant long-chain bases (LCBs) when assigning functions, such as signaling, to sphingolipids and their metabolites in plants.