- The stoichiometry of two LFNR isoforms(OsLFNR1 and OsLFNR2) plays an important role in electron partitioning between carbon fixation and nitrogen assimilation.
- Electrons might be transferred preferentially from Fd to the nitrogen assimilation pathway when OsLFNR2 accounts for a larger portion of the total LFNR.
- OsLFNR2 expression leads to the impairment of photosynthetic linear electron transport as well as Fd-dependent cyclic electron flow around photosystem I.
Figure 1. Isolation of rice FOX Arabidopsis lines with altered chlorophyll fluorescence. A, The left panel shows Arabidopsis wild-type (WT) and T2 seedlings of K17234. The right panel shows a pseudocolor image of the NPQ. B, Plants of the wild type and the T2 generation of K17234 in the adult stage..
- OsLFNR2 expressed in Arabidopsis.
- Scientists isolated the rice FOX(for fulllength cDNA overexpressor) Arabidopsismutants K17234 with altered chlorophyll fluorescence kinetics. The phenotypes of K17234 was apparently caused by expression of the rice LFNR2 gene. K17234 showed a pale green phenotype and that this phenotype was caused by the expression of OsLFNR2. Figure 1A shows the seedling plants and false-color images of nonphotochemical quenching (NPQ) in K17234. The false colors show the minimum NPQ in blue and the maximum in red. The NPQs K17234 were lower than in the wild type. K17234 exhibited pale green leaves at the seedling stage. As shown in Figure 1B, K17234 also exhibited growth defects and had paler green leaves in adult plants compared with the wild type. Chlorophyll content (μg chlorophyll mg-1 fresh weight) was lower in K17234 (0.97 ± 0.17) than in the wild type (1.73 ± 0.15). Concomitantly, a higher chlorophyll a/b ratio was observed in K17234 (3.39 ± 0.17) than in the wild type (3.13 ± 0.06). In K17234, endogenous expression of AtLFNR1 and AtLFNR2 might be affected by heterologous expression of the OsLFNR genes. The levels of AtLFNR1 and AtLFNR2 in K17234 decreased to 10% and 30% of those of the wild type, respectively. The results indicate that heterologous expression of OsLFNR fl-cDNAs results in a decreased level of AtLFNR mRNA in Arabidopsis.
Figure 2. Characterization of rice overexpression plants of OsLFNR2 .
- Overexpression of OsLFNR2 Genes in Rice
- Scientists observed 13 T0 transgenic plants of OsLFNR2 (OsLFNR2-overexpression in rice) and found that two of them were sterile, and six plants showed a pale green phenotype. Rice T1 plants of OsLFNR2OE showed growth defects (Fig. 2A) when they were grown in soil.
- Chlorophyll content (μg chlorophyll mg-1 fresh weight), when compared with that of the wild type (4.54 ± 0.62), was low in OsLFNR2OE (2.25 ± 0.47). The ratio of chlorophyll a/b was slightly higher in OsLFNR2OE (3.83 ± 0.18) than in the wild type (3.52 ± 0.12).
- Quantitative real-time RT-PCR analysis suggests that overexpression of OsLFNR2 gene causes the down-regulation of the endogenous LFNR1 in rice as observed in the rice FOX Arabidopsis lines(K17234).
- Proteins levels of OsLFNR1 and OsLFNR2 were determined by western blotting using the FNR antibody(Fig. 2D). Apparently, OsLFNR2OE accumulates more OsLFNR2 and less OsLFNR1 compared with the wild type.
- The gene expression profiles of OsLFNR2OE was investigated by microarray analysis. Many genes encoding nucleus-encoded PSI subunits were down-regulated, and the expression of genes encoding PSII subunits also decreased in OsLFNR2OE. Genes other than those encoding the subunits of the photosystems were also down-regulated, such as genes encoding light-harvesting proteins, chlorophyll biosynthesis-related genes, the Rubisco small subunit, and thylakoid ascorbate peroxidase.
- OsLFNR2-Expressing Arabidopsis and rice were impaired in linear electron transport and Fd-dependent cyclic electron flow around PSI.
- An alignment of LFNR1 and LFNR2 in rice and Arabidopsis is shown in Figure 3. Both in rice and Arabidopsis, LFNR1 and LFNR2 show high sequence identity at the amino acid level (80% identity between AtLFNR1 and AtLFNR2, 80% identity between OsLFNR1 and OsLFNR2) except for the N-terminal amino acids, corresponding to the chloroplast transit peptide signal sequences. The identity between rice and Arabidopsis is also high in LFNR1 and LFNR2 (80% identity between AtLFNR1 and OsLFNR1, 82% identity between AtLFNR2 and OsLFNR2). Several isoform-specific amino acids were seen as shown in the gray boxes.
Figure 3. Amino acid sequence alignment of LFNR proteins in rice and Arabidopsis.
- During photosynthesis, light energy is converted to chemical energy (in the form of ATP) through electron transport, and NADPH, a reducing agent, is also produced. In the final step of the linear electron transport of photosynthesis, ferredoxin NADP+-oxidoreductase (FNR) catalyzes the reduction of NADP+ by ferredoxin (Fd) and provides the reducing power for CO2 fixation in the Calvin cycle. FNR is supposed to be one of the limiting factors in photosynthetic electron transport. Through the analysis of FNR antisense tobacco (Nicotiana tabacum) plants, the amount of FNR has been shown to correlate with photosynthetic activity.
- FNR exists in a leaf form (LFNR) and a root form . There are two LFNR proteins (LFNR1 and LFNR2) in the Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) genomes. The overexpression of the OsLFNR1 and OsLFNR2 full-length cDNAs resulted in distinct phenotypes despite the high sequence similarity between them.
Labs working on this gene
- Plant Functional Genomics Research Group, RIKEN, Tsurumi-ku, Yokohama, Kanagawa 230–0045, Japan(M.H.-T., K.M., Y.H., M.K., M. Matsui)
- Technology Center, Okinawa Institute of Science and Technology Promotion Corporation, Onna-son, Kunigami-gun, Okinawa 904–0412, Japan (T.I.);
- Department of Applied Material and Life Science, Faculty of Engineering, Kanto Gakuin University, Kanazawa-ku, Yokohama, Kanagawa 236–8501, Japan (Y.K.);
- Faculty of Education and Integrated Arts and Sciences, Waseda University, Shinjuku, Tokyo 162–8480, Japan (K.S.)
- National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305–8602, Japan (M. Mori, H.H.)
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13
Higuchi-Takeuchi M, Ichikawa T, Kondou Y, Matsui K, Hasegawa Y, Kawashima M, Sonoike K, Mori M, Hirochika H, Matsui M. Functional analysis of two isoforms of leaf-type ferredoxin-NADP(+)-oxidoreductase in rice using the heterologous expression system of Arabidopsis. Plant Physiol. 2011 Sep;157(1):96-108. doi: 10.1104/pp.111.181248. Epub 2011 Jul 6. PubMed PMID: 21734114; PubMed Central PMCID: PMC3165901.
Hanke GT, Okutani S, Satomi Y, Takao T, Suzuki A, Hase T (2005) Multiple iso-proteins of FNR in Arabidopsis: evidence for different contributions to chloroplast function and nitrogen assimilation. Plant Cell Environ 28: 1146–1157