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Low CO 2 results in a rearrangement of carbon metabolism to support C 4 photosynthetic carbon assimilation in Thalassiosira pseudonana
Author(s) -
Kustka Adam B.,
Milligan Allen J.,
Zheng Haiyan,
New Ashley M.,
Gates Colin,
Bidle Kay D.,
Reinfelder John R.
Publication year - 2014
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.12926
Subject(s) - phosphoenolpyruvate carboxylase , phosphoenolpyruvate carboxykinase , thalassiosira pseudonana , decarboxylation , photosynthesis , biochemistry , chemistry , carbon fixation , metabolism , c4 photosynthesis , pyruvate carboxylase , biology , enzyme , ecology , phytoplankton , nutrient , catalysis
Summary The mechanisms of carbon concentration in marine diatoms are controversial. At low CO 2 , decreases in O 2 evolution after inhibition of phosphoenolpyruvate carboxylases ( PEPC s), and increases in PEPC transcript abundances, have been interpreted as evidence for a C 4 mechanism in Thalassiosira pseudonana , but the ascertainment of which proteins are responsible for the subsequent decarboxylation and PEP regeneration steps has been elusive. We evaluated the responses of T. pseudonana to steady‐state differences in CO 2 availability, as well as to transient shifts to low CO 2 , by integrated measurements of photosynthetic parameters, transcript abundances and quantitative proteomics. On shifts to low CO 2 , two PEPC transcript abundances increased and then declined on timescales consistent with recoveries of F v / F m , non‐photochemical quenching ( NPQ ) and maximum chlorophyll a ‐specific carbon fixation ( P max ), but transcripts for archetypical decarboxylation enzymes phosphoenolpyruvate carboxykinase ( PEPCK ) and malic enzyme ( ME ) did not change. Of 3688 protein abundances measured, 39 were up‐regulated under low CO 2 , including both PEPC s and pyruvate carboxylase ( PYC ), whereas ME abundance did not change and PEPCK abundance declined. We propose a closed‐loop biochemical model, whereby T. pseudonana produces and subsequently decarboxylates a C 4 acid via PEPC 2 and PYC , respectively, regenerates phosphoenolpyruvate ( PEP ) from pyruvate in a pyruvate phosphate dikinase‐independent (but glycine decarboxylase ( GDC )‐dependent) manner, and recuperates photorespiratory CO 2 as oxaloacetate ( OAA ).