Phosphoenolpyruvate carboxylase kinase is controlled by a similar signaling cascade in CAM and C(4) plants.
In Crassulacean acid metabolism (CAM) plants, phosphoenolpyruvate carboxylase (PEPC) is subject to day-night regulatory phosphorylation of a conserved serine residue in the plant enzyme's N-terminal domain. The dark increase in PEPC-kinase (PEPC-k) activity is under control of a circadian oscillator, via the enhanced expression of the corresponding gene (1). The signaling cascade leading to PEPC-k up-regulation was investigated in leaves and mesophyll cell protoplasts of the facultative, salt-inducible CAM species, Mesembryanthemum crystallinum. Mesophyll cell protoplasts had the same PEPC-k activity as leaves from which they were prepared (i.e., high at night, low during the day). However, unlike C(4) protoplasts (2), CAM protoplasts did not show marked PEPC-k up-regulation when isolated during the day and treated with a weak base such as NH(4)Cl. Investigations using various pharmacological reagents established the operation, in the darkened CAM leaf, of a PEPC-k cascade including the following components: a phosphoinositide-dependent phospholipase C (PI-PLC), inositol 1,4,5 P (IP(3))-gated tonoplast calcium channels, and a putative Ca(2+)/calmodulin protein kinase. These results suggest that a similar signaling machinery is involved in both C(4) (2, 3) and CAM plants to regulate PEPC-k activity, the phosphorylation state of PEPC, and, thus, carbon flux through this enzyme during CAM photosynthesis.
Bakrim
N
N
Institut de Biotechnologie des Plantes, UMR CNRS 8618, Université Paris-Sud, Orsay Cedex, 91405, France.
Brulfert
J
J
Vidal
J
J
Chollet
R
R
D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D019684:Magnoliopsida / Q000201:enzymology / Q000235:genetics*; D008293:Malates / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D018515:Plant Leaves / Q000201:enzymology; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D015854:Up-Regulation
D008293:Malates; D011994:Recombinant Proteins; C030298:malic acid; D015544:Inositol 1,4,5-Trisphosphate; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases; D010730:Phosphoenolpyruvate Carboxylase