Functional Analysis of Two Isoforms of Leaf-Type Ferredoxin-NADP⁺-Oxidoreductase in Rice Using the Heterologous Expression System of Arabidopsis

• Published in: Plant physiology (Bethesda) 2011-09, Vol.157 (1), p.96-108
• Main Authors: Higuchi-Takeuchi, Mieko, Ichikawa, Takanari, Kondou, Youichi, Matsui, Keiko, Hasegawa, Yukako, Kawashima, Mika, Sonoike, Kintake, Mori, Masaki, Hirochika, Hirohiko, Matsui, Minami
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Arabidopsis; Arabidopsis - genetics; Arabidopsis thaliana; BIOENERGETICS AND PHOTOSYNTHESIS; Biological and medical sciences; Calvin cycle; carbon; chemistry; chlorophyll; Chlorophyll - metabolism; Chlorophylls; Chloroplasts; complementary DNA; DNA, Complementary; electron transfer; Electron Transport; electrons; enzymology; Ferredoxin-NADP Reductase; Ferredoxin-NADP Reductase - chemistry; Ferredoxin-NADP Reductase - genetics; Ferredoxin-NADP Reductase - metabolism; Fluorescence; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Genes, Plant; genetics; glutamates; Isoenzymes; Isoenzymes - metabolism; metabolism; Molecular Sequence Data; nitrite reductase; Nitrogen; nitrogen fixation; Oryza; Oryza - enzymology; Oryza - genetics; Oryza sativa; Phenotypes; photosystem I; Plant growth; Plant Leaves; Plant Leaves - enzymology; Plant physiology and development; Plants; Protein isoforms; Rice; RNA, Messenger; RNA, Messenger - genetics; Sequence Homology, Amino Acid; Spectrometry, Fluorescence; stoichiometry; Thylakoids; transport proteins
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.111.181248

Ferredoxin-NADP⁺-oxidoreductase (FNR) mediates electron transfer between ferredoxin (Fd) and NADP⁺; therefore, it is a key enzyme that provides the reducing power used in the Calvin cycle. Other than FNR, nitrite reducíase, sulfite reducíase, glutamate synthase, and Fd-thioredoxin reducíase also accept electrons from Fd, an electron carrier protein in the stroma. Therefore, the regulation of electron partitioning in the chloroplast is important for photosynthesis and other metabolic pathways. The regulatory mechanism of electron partitioning, however, remains to be elucidated. We found, by taking advantage of a gain-of-function approach, that expression of two rice (Oryza sativa) full-length cDNAs of leaf-type FNRs (OsLFNR1 and OsLFNR2) led to altered chlorophyll fluorescence and growth in Arabidopsis (Arabidopsis thaliana) and rice. We revealed that overexpression of the OsLFNR1 and OsLFNR2 full-length cDNAs resulted in distinct phenotypes despite the high sequence similarity between them. Expression of OsLFNR1 affected the nitrogen assimilation pathway without inhibition of photosynthesis under normal conditions. On the other hand, OsLFNR2 expression led to the impairment of photosynthetic linear electron transport as well as Fd-dependent cyclic electron flow around photosystem I. The endogenous protein level of OsLFNR was found to be suppressed in both OsLFNR1-and OsLFNR2-overexpressing rice plants, leading to changes in the stoichiometry of the two LFNR isoforms within the thylakoid and soluble fractions. Thus, we propose that the stoichiometry of two LFNR isoforms plays an important role in electron partitioning between carbon fixation and nitrogen assimilation.