Link between light and fatty acid synthesis: Thioredoxin-linked reductive activation of plastidic acetyl-CoA carboxylase

Abstract

Fatty acid synthesis in chloroplasts is regulated by light. The synthesis of malonyl-CoA, which is catalyzed by acetyl-CoA carboxylase (ACCase) and is the first committed step, is modulated by light͞dark. Plants have ACCase in plastids and the cytosol. To determine the possible involvement of a redox cascade in light͞dark modulation of ACCase, the effect of DTT, a known reductant of S-S bonds, was examined in vitro for the partially purified ACCase from pea plant. Only the plastidic ACCase was activated by DTT. This enzyme was activated in vitro more efficiently by reduced thioredoxin, which is a transducer of redox potential during illumination, than by DTT alone. Chloroplast thioredoxin-f activated the enzyme more efficiently than thioredoxin-m. The ACCase also was activated by thioredoxin reduced enzymatically with NADPH and NADP-thioredoxin reductase. These findings suggest that the reduction of ACCase is needed for activation of the enzyme, and a redox potential generated by photosynthesis is involved in its activation through thioredoxin as for enzymes of the reductive pentose phosphate cycle. The catalytic activity of ACCase was maximum at pH 8 and 2-5 mM Mg 2؉ , indicating that light-produced changes in stromal pH and Mg 2؉ concentration modulate ACCase activity. These results suggest that light directly modulates a regulatory site of plastidic prokaryotic form of ACCase via a signal transduction pathway of a redox cascade and indirectly modulates its catalytic activity via stromal pH and Mg 2؉ concentration. A redox cascade is likely to link between light and fatty acid synthesis, resulting in coordination of fatty acid synthesis with photosynthesis.

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

“…In addition to ADP-glucose pyrophosphorylase, five of the previously reported targets in Table 2 have been biochemically linked to Trx: acetyl-CoA carboxylase (35), cyclophilin (49), peroxiredoxin BAS1 (50), protein disulfide isomerase (51,52), and thiosulfate sulfurtransferase (53). Two previously reported amyloplast targets, glucose-6-phosphate dehydrogenase (19) and ␣-glucan, water dikinase (21), were not confirmed in our work.…”

“…The identification of acyl-[acyl-carrier-protein] thioesterase as a potential target protein indicates that Trx has broader control of de novo fatty acid synthesis than was previously thought. Accordingly, with addition of thiolesterase, Trx appears to control the terminal step of the pathway in addition to the previously established first step catalyzed by acetyl-CoA carboxylase (35). Amino acid biosynthesis.…”

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

“…It will be interesting to determine whether T6P also regulates other thioredoxin-dependent processes in the plastid, such as fatty acid (35) or amino acid synthesis (36). This may allow global control of diverse pathways of carbon utilization in plants in response to short-term changes in the carbon status.…”

A Family of Negative Regulators Targets the Committed Step of de Novo Fatty Acid Biosynthesis

“…HetACCase is activated by light, during which its activity increases severalfold in the plastid. This activation occurs within minutes and is reportedly due to the increase in stromal pH from 7.0 to 8.0 (Hunter and Ohlrogge, 1998) and thioredoxin-dependent reduction of a disulfide bond in CT (Sasaki et al, 1997;Kozaki et al, 2001). HetACCase activity is also suppressed by feedback inhibition through increased levels of acyl-acyl carrier protein (Davis and Cronan, 2001;Andre et al, 2012).…”