The fou2 mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium.
The SV channel encoded by the TPC1 gene represents a Ca(2+)- and voltage-dependent vacuolar cation channel. Point mutation D454N within TPC1, named fou2 for fatty acid oxygenation upregulated 2, results in increased synthesis of the stress hormone jasmonate. As wounding causes Ca2+ signals and cytosolic Ca2+ is required for SV channel function, we here studied the Ca(2+)-dependent properties of this major vacuolar cation channel with Arabidopsis thaliana mesophyll vacuoles. In patch clamp measurements, wild-type and fou2 SV channels did not exhibit differences in cytosolic Ca2+ sensitivity and Ca2+ impermeability. K+ fluxes through wild-type TPC1 were reduced or even completely faded away when vacuolar Ca2+ reached the 0.1-mm level. The fou2 protein under these conditions, however, remained active. Thus, D454N seems to be part of a luminal Ca2+ recognition site. Thereby the SV channel mutant gains tolerance towards elevated luminal Ca2+. A three-fold higher vacuolar Ca/K ratio in the fou2 mutant relative to wild-type plants seems to indicate that fou2 can accumulate higher levels of vacuolar Ca(2+) before SV channel activity vanishes and K(+) homeostasis is impaired. In response to wounding fou2 plants might thus elicit strong vacuole-derived cytosolic Ca2+ signals resulting in overproduction of jasmonate.
Beyhl
Diana
D
Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute, University of Würzburg, Würzburg, Germany.
Hörtensteiner
Stefan
S
Martinoia
Enrico
E
Farmer
Edward E
EE
Fromm
Jörg
J
Marten
Irene
I
Hedrich
Rainer
R
D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011188:Potassium / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism / Q000502:physiology; D000097903:Two-Pore Channels
D029681:Arabidopsis Proteins; D002118:Calcium; D015220:Calcium Channels; D011188:Potassium; C498240:TPC1 protein, Arabidopsis; D000097903:Two-Pore Channels