Transgenic Tobacco Plants Overexpressing Chloroplastic Ferredoxin-NADP(H) Reductase Display Normal Rates of Photosynthesis and Increased Tolerance to Oxidative Stress

Abstract

(M.P., H.T., M.-R.H.)Ferredoxin-NADP(H) reductase (FNR) catalyzes the last step of photosynthetic electron transport in chloroplasts, driving electrons from reduced ferredoxin to NADP 1 . This reaction is rate limiting for photosynthesis under a wide range of illumination conditions, as revealed by analysis of plants transformed with an antisense version of the FNR gene. To investigate whether accumulation of this flavoprotein over wild-type levels could improve photosynthetic efficiency and growth, we generated transgenic tobacco (Nicotiana tabacum) plants expressing a pea (Pisum sativum) FNR targeted to chloroplasts. The alien product distributed between the thylakoid membranes and the chloroplast stroma. Transformants grown at 150 or 700 mmol quanta m 22 s 21 displayed wild-type phenotypes regardless of FNR content. Thylakoids isolated from plants with a 5-fold FNR increase over the wild type displayed only moderate stimulation (approximately 20%) in the rates of electron transport from water to NADP 1 . In contrast, when donors of photosystem I were used to drive NADP 1 photoreduction, the activity was 3-to 4-fold higher than the wild-type controls. Plants expressing various levels of FNR (from 1-to 3.6-fold over the wild type) failed to show significant differences in CO 2 assimilation rates when assayed over a range of light intensities and CO 2 concentrations. Transgenic lines exhibited enhanced tolerance to photooxidative damage and redox-cycling herbicides that propagate reactive oxygen species. The results suggest that photosynthetic electron transport has several rate-limiting steps, with FNR catalyzing just one of them.

N-Terminal Structure of Maize Ferredoxin:NADP+ Reductase Determines Recruitment into Different Thylakoid Membrane Complexes

“…Previous transformation of tobacco (Nicotiana tabacum) with pea FNR did not yield a phenotypic difference (Rodriguez et al, 2007), indicating that factors other than FNR limit photosynthesis in tobacco. It was recently reported that expression of rice (Oryza sativa) FNR2 in Arabidopsis perturbed both LET and CET, while rice FNR1 disturbed N assimilation (Higuchi-Takeuchi et al, 2011).…”

Metabolome and Photochemical Analysis of Rice Plants Overexpressing Arabidopsis NAD Kinase Gene

“…However, increases in protein levels of photosynthetic electron transport chain components, except for overexpression of cytochrome c6 (Cyt c 6 ) from the red alga Porphyra yezoensis, did not result in increase in FPSII and plant growth [ferredoxin NADP(H) oxidoreductase, Rodriguez et al, 2007;ferredoxin, Yamamoto et al, 2006]. Overexpression of Porphyra Cyt c 6 in Arabidopsis resulted in enhanced ETR through PSII and plant growth and an increase in NADPH and ATP (Chida et al, 2007).…”

Energy Conductance from Thylakoid Complexes to Stromal Reducing Equivalents

“…Studies in vivo have revealed that suppression of FNR expression leads to increased susceptibility to photo-oxidative damage, impaired plant growth and lowered photosynthetic activity of transgenic plants (Hajirezaei et al, 2002;Palatnik et al, 2003). On the other hand, overexpression of FNR results in slightly increased rates of electron transport from water to NADP+ and increased tolerance to oxidative stress (Rodriguez et al, 2007). Based on isoelectric focusing and SDS-PAGE the proteome of wheat has revealed four distinct leaf FNR isoforms that can be divided into two groups, FNRI and FNRII.…”

“…The redox poise of the NADP(H) pool is also likely to regulate photosynthetic electron transfer activity in order to balance production and consumption of reducing equivalents, and thereby to limit production of ROS in the chloroplasts (Hald et al, 2008). Overexpression of FNR, however, did not markedly up-regulate the rate of NADP + photoreduction or CO 2 assimilation, but showed increased tolerance to photodamage (Rodriguez et al, 2007). Fig.…”

“…Overexpression of FNR in transgenic plants causes enhanced tolerance to photo-oxidative damage and herbicides that propagate reactive oxygen species (Rodriguez et al, 2007). On the other hand, antisense repression of FNR renders transgenic plants abnormally prone to photo-oxidative stress (Palatnik et al, 2003).…”