Phosphorylation of Arabidopsis transketolase at Ser428 provides a potential paradigm for the metabolic control of chloroplast carbon metabolism

Abstract

Calcium is an important second messenger in eukaryotic cells that regulates many different cellular processes. To elucidate calcium regulation in chloroplasts, we identified the targets of calcium-dependent phosphorylation within the stromal proteome. A 73 kDa protein was identified as one of the most dominant proteins undergoing phosphorylation in a calcium-dependent manner in the stromal extracts of both Arabidopsis and Pisum. It was identified as TKL (transketolase), an essential enzyme of both the Calvin–Benson–Bassham cycle and the oxidative pentose phosphate pathway. Calcium-dependent phosphorylation of both Arabidopsis isoforms (AtTKL1 and AtTKL2) could be confirmed in vitro using recombinant proteins. The phosphorylation is catalysed by a stroma-localized protein kinase, which cannot utilize GTP. Phosphorylation of AtTKL1, the dominant isoform in most tissues, occurs at a serine residue that is conserved in TKLs of vascular plants. By contrast, an aspartate residue is present in this position in cyanobacteria, algae and mosses. Characterization of a phosphomimetic mutant (S428D) indicated that Ser428 phosphorylation exerts significant effects on the enzyme's substrate saturation kinetics at specific physiological pH values. The results of the present study point to a role for TKL phosphorylation in the regulation of carbon allocation.

Proteomic and Metabolomic Analysis of a Drought Tolerant Soybean Cultivar from Brazilian Savanna

“…A notable distinct protein expression profile between the genotypes was also observed for the protein Transketolase (Figures 7 and 8 Tables S6 and S7) and experimentally by Rocha [33].…”

“…Hierarchical clustering by ClueGO revealed phosphoproteins related to some biological processes that were specific for the genotypes ( Supplementary Figures S4 and S6). As reported by Rocha [33], phosphorylation could regulate the behavior of the soybean's response to tolerance. The chloroplastic drought-induced stress protein was observed in different phosphorylated isoforms stained in the gel (32 KD).…”

Integration of a constraint-based metabolic model of Brassica napus developing seeds with 13C-metabolic flux analysis

“…Yet, it has been reported that in the A. thaliana genome only plastid isoforms of transketolase and transaldolase are known (Eicks et al, 2002 ). So far no cytosolic isoforms have been found in A. thaliana and recently transketolase (AT2G45290, AT3G60750) has been localized to the chloroplast based on in vivo protein tagging (YFP) (Rocha et al, 2014 ). In our revision the reactions TKT1_c, TKT2_c, and TALDO_c have no genes associated.…”

The membrane proteome of male gametophyte in Solanum lycopersicum

“…Moreover, we detected a plastid localized Arf-type small GTPase (Solyc12g099080), which is functionally categorized as a protein involved in targeting by MapMan. Two plastidlocalized transketolase (Solyc05g050970 and Solyc10g018300) participating in energy related processes were also identified [87] (Table 3). However, we did not find any components of the protein translocation system or of the photosystems.…”