Reference "Pyruvate,Orthophosphate dikinase in leaves and chloroplasts of c(3) plants undergoes light-/dark-induced reversible phosphorylation"

Reference ID

6556

Title

Pyruvate,Orthophosphate dikinase in leaves and chloroplasts of c(3) plants undergoes light-/dark-induced reversible phosphorylation

Source

Plant physiology, 2002, vol. 128, pp. 1368-1378

Authors (12)

Chastain-C-J	Fries-J-P	Vogel-J-A	Randklev-C-L
Vossen-A-P	Dittmer-S-K	Watkins-E-E	Fiedler-L-J
Wacker-S-A	Meinhover-K-C	Sarath-G	Chollet-R

Abstract

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 (occurring much more slowly (>/=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.