PT  - JOURNAL ARTICLE
AU  - Jiying Li
AU  - Sarathi M. Weraduwage
AU  - Alyssa L. Preiser
AU  - Sean E. Weise
AU  - Deserah D. Strand
AU  - John E. Froehlich
AU  - David M. Kramer
AU  - Jianping Hu
AU  - Thomas D. Sharkey
TI  - Loss of Peroxisomal Hydroxypyruvate Reductase Inhibits Triose Phosphate Isomerase but Stimulates Cyclic Photosynthetic Electron Flow and the Glc-6P-Phosphate Shunt
AID  - 10.1101/278580
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 278580
4099  - http://biorxiv.org/content/early/2018/03/08/278580.short
4100  - http://biorxiv.org/content/early/2018/03/08/278580.full
AB  - The oxygenation of ribulose 1,5-bisphosphate by Rubisco is the first step in photorespiration and reduces the efficiency of photosynthesis in C3 plants. Our recent data indicates that mutants in photorespiration have increased rates of photosynthetic cyclic electron flow around photosystem I. We investigated mutant lines lacking peroxisomal hydroxypyruvate reductase to determine if there are connections between 2-PG accumulation and cyclic electron flow. We found that 2-PG is a competitive inhibitor of triose phosphate isomerase (TPI), an enzyme in the Calvin-Benson cycle that converts glyceraldehyde 3-phosphate to dihydroxyacetone phosphate. This block in metabolism could be overcome if glyceraldehyde 3-phosphate is exported to the cytosol where the cytosolic triose phosphate isomerase could convert it to dihydroxyacetone phosphate. We found evidence that carbon is reimported as Glc-6P-phosphate forming a cytosolic bypass around the block of stromal TPI. However, this also stimulates a Glc-6P-phosphate shunt, which consumes ATP, which can be compensated by higher rates of cyclic electron flow.Once Sentence Summary Triose phosphate isomerase is inhibited in plants lacking hydroxypyruvate reductase 1 and this is overcome by exporting triose phosphate to the cytosol and importing Glc-6P, which stimulates a Glc-6P-phosphate shunt and cyclic electron flow.