Acclimation of metabolism to light in Arabidopsis thaliana: The glucose 6-phosphate/phosphate translocator GPT2 directs metabolic acclimation

Abstract

Mature leaves of plants transferred from low to high light typically increase their photosynthetic capacity. In Arabidopsis thaliana, this dynamic acclimation requires expression of GPT2, a glucose 6-phosphate/phosphate translocator. Here, we examine the impact of GPT2 on leaf metabolism and photosynthesis. Plants of wild type and of a GPT2 knockout (gpt2.2) grown under low light achieved the same photosynthetic rate despite having different metabolic and transcriptomic strategies. Immediately upon transfer to high light, gpt2.2 plants showed a higher rate of photosynthesis than wild-type plants (35%); however, over subsequent days, wild-type plants acclimated photosynthetic capacity, increasing the photosynthesis rate by 100% after 7d. Wild-type plants accumulated more starch than gpt2.2 plants throughout acclimation. We suggest that GPT2 activity results in the net import of glucose 6-phosphate from cytosol to chloroplast, increasing starch synthesis. There was clear acclimation of metabolism, with short-term changes typically being reversed as plants acclimated. Distinct responses to light were observed in wild-type and gpt2.2 leaves. Significantly higher levels of sugar phosphates were observed in gpt2.2. We suggest that GPT2 alters the distribution of metabolites between compartments and that this plays an essential role in allowing the cell to interpret environmental signals. Acclimation to changes in the environment are crucial to optimising plant growth and productivity. In Arabidopsis thaliana, the glucose-6-phosphate/phosphate translocator GPT2 plays an important role in the acclimation to increased irradiance. Here we show that expression of GPT2 influences the partitioning of carbon between different storage pools, enhancing starch synthesis. Acclimation of metabolism occurs but is distinct in plants expressing or lacking GPT2.y