Phosphoglycerate Kinases Are Co-Regulated to Adjust Metabolism and to Optimize Growth.

In plants, phosphoglycerate kinase (PGK) converts 1,3-bisphosphoglycerate into 3-phosphoglycerate in glycolysis but also participates in the reverse reaction in gluconeogenesis and the Calvin-Benson cycle. In the databases, we found three genes that encode putative PGKs. Arabidopsis () PGK1 was localized exclusively in the chloroplasts of photosynthetic tissues, while PGK2 was expressed in the chloroplast/plastid of photosynthetic and nonphotosynthetic cells. PGK3 was expressed ubiquitously in the cytosol of all studied cell types. Measurements of carbohydrate content and photosynthetic activities in PGK mutants and silenced lines corroborated that PGK1 was the photosynthetic isoform, while PGK2 and PGK3 were the plastidial and cytosolic glycolytic isoforms, respectively. The knockdown mutant displayed reduced growth, lower photosynthetic capacity, and starch content. The knockout mutant was characterized by reduced growth but higher starch levels than the wild type. The double mutant was bigger than and displayed an intermediate phenotype between the two single mutants in all measured biochemical and physiological parameters. Expression studies in mutants showed that and were down-regulated in and , respectively. These results indicate that the down-regulation of photosynthetic activity could be a plant strategy when glycolysis is impaired to achieve metabolic adjustment and optimize growth. The double mutants of and the triose-phosphate transporter ( displayed a drastic growth phenotype, but they were viable. This implies that other enzymes or nonspecific chloroplast transporters could provide 3-phosphoglycerate to the cytosol. Our results highlight both the complexity and the plasticity of the plant primary metabolic network.