Decreased Expression of Cytosolic Pyruvate Kinase in Potato Tubers Leads to a Decline in Pyruvate Resulting in an in Vivo Repression of the Alternative Oxidase  

Abstract

The aim of this work was to investigate the effect of decreased cytosolic pyruvate kinase (PKc) on potato (Solanum tuberosum) tuber metabolism. Transgenic potato plants with strongly reduced levels of PKc were generated by RNA interference gene silencing under the control of a tuber-specific promoter. Metabolite profiling showed that decreased PKc activity led to a decrease in the levels of pyruvate and some other organic acids involved in the tricarboxylic acid cycle. Flux analysis showed that this was accompanied by changes in carbon partitioning, with carbon flux being diverted from glycolysis toward starch synthesis. However, this metabolic shift was relatively small and hence did not result in enhanced starch levels in the tubers. Although total respiration rates and the ATP to ADP ratio were largely unchanged, transgenic tubers showed a strong decrease in the levels of alternative oxidase (AOX) protein and a corresponding decrease in the capacity of the alternative pathway of respiration. External feeding of pyruvate to tuber tissue or isolated mitochondria resulted in activation of the AOX pathway, both in the wild type and the PKc transgenic lines, providing direct evidence for the regulation of AOX by changes in pyruvate levels. Overall, these results provide evidence for a crucial role of PKc in the regulation of pyruvate levels as well as the level of the AOX in heterotrophic plant tissue, and furthermore reveal that these parameters are interlinked in vivo.

Combined Noninvasive Imaging and Modeling Approaches Reveal Metabolic Compartmentation in the Barley Endosperm

“…Similar conclusions were drawn from studies on photosynthetically active Arabidopsis tissues (Lee et al, 2008) and metabolic changes in response to waterlogging in Lotus japonicus (Rocha et al, 2010). By removing pyruvate, the activation of ethanol/lactate fermentation is inhibited ( Figure 4A), and the stimulation of alternative oxidase activity can be avoided (Oliver et al, 2008). Ala synthesis under endogenous oxygen limitation is regarded as a means to maintain glycolysis and energy provision.…”

A Metabolomic Approach to Study Major Metabolite Changes during Acclimation to Limiting CO2 in Chlamydomonas reinhardtii

“…The expression of PK3 and PK5 is largely unchanged and may complicate the picture. In potato (Solanum tuberosum) tubers, however, it has been shown that gene silencing by RNA interference of the most highly expressed cytosolic PK resulted in a decreased pyruvate synthesis, even though another four isoforms of cytosolic PK were present (Oliver et al, 2008). In C. reinhardtii, the isoform PK1 has about three times more supporting EST sequences in the National Center for Biotechnology Information database than the other isoforms, giving good support to this being the most abundant cytosolic PK.…”

Metabolic Control of Redox and Redox Control of Metabolism in Plants

“…Furthermore, a mitochondrially localized Trx has been demonstrated to be able to reduce this disulfide bond (108). Once reduced, AOX is sensitive to activation by specific organic acids, most notably pyruvate (229,260,360). Recent studies indicate that this effect is due to the enzyme's apparent Vmax resulting from the ability of pyruvate to stabilize the active AOX (54).…”