Pyruvate,orthophosphate dikinase in leaves and chloroplasts of C(3) plants undergoes light-/dark-induced reversible phosphorylation.
Pyruvate,orthophosphate (Pi) dikinase (PPDK) is best recognized as a chloroplastic C(4) cycle enzyme. As one of the key regulatory foci for controlling flux through this photosynthetic pathway, it is strictly and reversibly regulated by light. This light/dark modulation is mediated by reversible phosphorylation of a conserved threonine residue in the active-site domain by the PPDK regulatory protein (RP), a bifunctional protein kinase/phosphatase. PPDK is also present in C(3) plants, although it has no known photosynthetic function. Nevertheless, in this report we show that C(3) PPDK in leaves of several angiosperms and in isolated intact spinach (Spinacia oleracea) chloroplasts undergoes light-/dark-induced changes in phosphorylation state in a manner similar to C(4) dikinase. In addition, the kinetics of this process closely resemble the reversible C(4) process, with light-induced dephosphorylation occurring rapidly (< or =15 min) and dark-induced phosphorylation occurring much more slowly (> or =30-60 min). In intact spinach chloroplasts, light-induced dephosphorylation of C(3) PPDK was shown to be dependent on exogenous Pi and photosystem II activity but independent of electron transfer from photosystem I. These in organello results implicate a role for stromal pools of Pi and adenylates in regulating the reversible phosphorylation of C(3)-PPDK. Last, we used an in vitro RP assay to directly demonstrate ADP-dependent PPDK phosphorylation in desalted leaf extracts of the C(3) plants Vicia faba and rice (Oryza sativa). We conclude that an RP-like activity mediates the light/dark modulation of PPDK phosphorylation state in C(3) leaves and chloroplasts and likely represents the ancestral isoform of this unusual and key C(4) pathway regulatory "converter" enzyme.
Chastain
Chris J
CJ
Department of Biology, Minnesota State University, Moorhead, MN 56563, USA. chastain@mhd1.mnstate.edu
Fries
Jason P
JP
Vogel
Julie A
JA
Randklev
Christa L
CL
Vossen
Adam P
AP
Dittmer
Sharon K
SK
Watkins
Erin E
EE
Fiedler
Lucas J
LJ
Wacker
Sarah A
SA
Meinhover
Katherine C
KC
Sarath
Gautam
G
Chollet
Raymond
R
D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology*; D003624:Darkness; D007887:Fabaceae / Q000201:enzymology; D008027:Light; D019684:Magnoliopsida / Q000145:classification / Q000201:enzymology*; D008954:Models, Biological; D012275:Oryza / Q000201:enzymology; D010710:Phosphates / Q000378:metabolism; D010728:Phosphoenolpyruvate / Q000378:metabolism; D010766:Phosphorylation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000201:enzymology*; D011772:Pyruvate, Orthophosphate Dikinase / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism; D018724:Spinacia oleracea / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology
D010710:Phosphates; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D010728:Phosphoenolpyruvate; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D011772:Pyruvate, Orthophosphate Dikinase