Sphingolipid signalling in Arabidopsis guard cells involves heterotrimeric G proteins.
In animals, the sphingolipid metabolite sphingosine-1-phosphate (S1P) functions as both an intracellular messenger and an extracellular ligand for G-protein-coupled receptors of the S1P receptor family, regulating diverse biological processes ranging from cell proliferation to apoptosis. Recently, it was discovered in plants that S1P is a signalling molecule involved in abscisic acid (ABA) regulation of guard cell turgor. Here we report that the enzyme responsible for S1P production, sphingosine kinase (SphK), is activated by ABA in Arabidopsis thaliana, and is involved in both ABA inhibition of stomatal opening and promotion of stomatal closure. Consistent with this observation, inhibition of SphK attenuates ABA regulation of guard cell inward K(+) channels and slow anion channels, which are involved in the regulation of stomatal pore size. Surprisingly, S1P regulates stomatal apertures and guard cell ion channel activities in wild-type plants, but not in knockout lines of the sole prototypical heterotrimeric G-protein alpha-subunit gene, GPA1 (refs 5, 6, 7-8). Our results implicate heterotrimeric G proteins as downstream elements in the S1P signalling pathway that mediates ABA regulation of stomatal function, and suggest that the interplay between S1P and heterotrimeric G proteins represents an evolutionarily conserved signalling mechanism.
Coursol
Sylvie
S
Department of Biology, Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802-5301, USA.
Fan
Liu-Min
LM
Le Stunff
Hervé
H
Spiegel
Sarah
S
Gilroy
Simon
S
Assmann
Sarah M
SM
D000040:Abscisic Acid / Q000494:pharmacology; D000838:Anions / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000378:metabolism; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013107:Sphingolipids / Q000378:metabolism / Q000494:pharmacology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000099157:Sphingosine Kinase
D000040:Abscisic Acid; D000838:Anions; D020962:Heterotrimeric GTP-Binding Proteins; D007473:Ion Channels; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D011188:Potassium; D013107:Sphingolipids; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate