Downregulation of ferredoxin-NADP+ oxidoreductase enhances oxidized pentose phosphate pathway via NADPH/NADP+ ratio in the strong resurrection intertidal red alga Neopyropia yezoensis with economic value

Abstract

Ferredoxin-NADP+ oxidoreductase (FNR) is involved in reducing Fd in linear electron transportation (LET) in chloroplast. While the oxidized pentose phosphate pathway (OPPP) occurred in cytoplasm has close relationship with cyclic electron transportation (CET) under stress condition. However, whether FNR and OPPP cooperate with each other, and in what way they are associated remains unclear. In this study, Neopyropia yezoensis, a strong resurrection red macroalga, was used to study the relationship between FNR and OPPP. FNR genetic transformation strains of N. yezoensis, fnrOE (overexpression) and fnrSi (silence) were obtained. The results showed that the growth rate of fnrSi was reduced remarkably. The expression level of genes encoding key enzymes in OPPP and enzyme activity of G6PDH were up regulated in transgenic strains, indicating the enhancement of OPPP. Besides, the NADPH and NADP+ content in WT and transgenic lines were also measured. Y (I) of both fnrOE and fnrSi decreased significantly under dark treatment, indicating that FNR content synergistically affected CET pathway with OPPP in N. yezoensis. All the results indicated that changes of FNR content could enhance OPPP, which further promote the CET operation. This is the first time to find the close relationship between photosynthetic electron transportation and carbohydrate metabolism in strong resurrection plant.