Editors' ChoicePlant biology

Sphingolipids and G Proteins Prevent Dehydration

Science's STKE  10 Jun 2003:
Vol. 2003, Issue 186, pp. tw221-TW221
DOI: 10.1126/stke.2003.186.tw221

Sphingolipids have emerged as signaling molecules in plants and animals. In animals, sphingosine 1-phosphate (S1P) is produced in response to activation of sphingosine kinase and can be released from cells to stimulate G protein-coupled receptors (GPCRs). In plants, S1P stimulated stomatal closure, which is a mechanism by which plants can decrease water loss from leaves and CO2 uptake into leaves during times of drought and stress. Coursol et al. show that in Arabidopsis abscisic acid (ABA)-mediated inhibition of K+ current, and stimulation of anionic current was inhibited in guard cell protoplasts treated with inhibitors of mammalian sphingosine kinase. Furthermore, stomatal closure in response to ABA was also inhibited by blocking sphingosine kinase activity. Sphingosine kinase activity was detected in lysates from leaves, mesophyll cell protoplasts, and guard cell protoplasts, and production of S1P was stimulated by ABA. The ability of S1P to stimulate stomatal closure and to modulate K+ and anionic currents was lost in cells deficient for the G protein alpha subunit GPA1. In spite of the involvement of this, the authors mention other evidence--including pharmacologic differences in the mammalian and plant S1P response and the lack of conservation between the plant GPCRs and mammalian S1P receptors--and propose that the S1P signal in plants may be mediated without the involvement of a GPCR.

S. Coursol, L.-M. Fan, H. Le Stunff, S. Spiegel, S. Gilroy, S. M. Assmann, Sphingolipid signalling in Arabidopsis guard cells involves heterotrimeric G proteins. Nature 423, 651-654 (2003). [Online Journal]