Comparative analysis of leaf‐type ferredoxin‐NADP⁺ oxidoreductase isoforms in Arabidopsis thaliana

Abstract

SummaryPhysiological roles of the two distinct chloroplast-targeted ferredoxin-NADP + oxidoreductase (FNR) isoforms in Arabidopsis thaliana were studied using T-DNA insertion line fnr1 and RNAi line fnr2. In fnr2 FNR1 was present both as a thylakoid membrane-bound form and as a soluble protein, whereas in fnr1 the FNR2 protein existed solely in soluble form in the stroma. The fnr2 plants resembled fnr1 in having downregulated photosynthetic properties, expressed as low chlorophyll content, low accumulation of photosynthetic thylakoid proteins and reduced carbon fixation rate when compared with wild type (WT). Under standard growth conditions the level of F 0 'rise' and the amplitude of the thermoluminescence afterglow (AG) band, shown to correlate with cyclic electron transfer (CET), were reduced in both fnr mutants. In contrast, when plants were grown under low temperatures, both fnr mutants showed an enhanced rate of CET when compared with the WT. These data exclude the possibility that distinct FNR isoforms feed electrons to specific CET pathways. Nevertheless, the fnr2 mutants had a distinct phenotype upon growth at low temperature. The fnr2 plants grown at low temperature were more tolerant against methyl viologen (MV)-induced cell death than fnr1 and WT. The unique tolerance of fnr2 plants grown at low temperature to oxidative stress correlated with an increased level of reduced ascorbate and reactive oxygen species (ROS) scavenging enzymes, as well as with a scarcity in the accumulation of thylakoid membrane protein complexes, as compared with fnr1 and WT. These results emphasize a critical role for FNR2 in the redistribution of electrons to various reducing pathways, upon conditions that modify the photosynthetic capacity of the plant.

Chloroplast lipid droplet type II NAD(P)H quinone oxidoreductase is essential for prenylquinone metabolism and vitamin K 1 accumulation

“…2A shows the afterglow thermoluminescence band, induced by farred preillumination, that corresponds to a heat-induced back electron transfer to the PQ pool in the dark (23). In Arabidopsis, this pathway has been shown to reflect mainly the NDH activity (24,25), as confirmed here by the strong reduction of this band in ndh1. Again, no difference was found between WT and ndc1.…”

Systemic Cold Stress Adaptation of Chlamydomonas reinhardtii

“…Thioredoxins are labile to low temperatures, with a high unfolding constant (6), so its quick denaturation may lead to degradation and recycling, while ferredoxins, with a much more lower unfolding constant and resistant to temperature changes, became over-accumulated. These biophysical properties of ferredoxins may explain its known function of controlling oxidative damage and maintaining the integrity of thylakoid membranes and photosynthesis during cold stress (92,93). The ferredoxin and thioredoxin system is reported to have also important roles in light perception and redox signaling pathways within the chloroplast (94).…”

Energy Conductance from Thylakoid Complexes to Stromal Reducing Equivalents

“…Recently, also formation of large (~ 330 kDa) FNR oligomers, devoid of other proteins, has been documented (Grzyb et al, 2008). Inactivation of one chloroplast FNR isoform did not result in upregulation of the expression of the other, neither at the level of transcription nor translation (Lintala et al, 2007;Lintala et al, 2009). Inactivation of either FNR gene resulted in general downregulation of the photosynthetic machinery, but neither of the isoforms showed any specific function in LEF or CEF of photosynthesis, or other alternative electron transfer reactions (Lintala et al, 2007;Lintala et al, 2009).…”

“…Inactivation of one chloroplast FNR isoform did not result in upregulation of the expression of the other, neither at the level of transcription nor translation (Lintala et al, 2007;Lintala et al, 2009). Inactivation of either FNR gene resulted in general downregulation of the photosynthetic machinery, but neither of the isoforms showed any specific function in LEF or CEF of photosynthesis, or other alternative electron transfer reactions (Lintala et al, 2007;Lintala et al, 2009). Growth of the fnr knock-out plants under unfavorable conditions revealed a unique role for FNR2 in redistribution of electrons to various redox reactions ).…”

“…When the amount of FNR was artificially reduced by antisense or silencing techniques (Hajirezaei et al, 2002;Lintala et al, 2009), or by interruption of a FNR gene by T-DNA (Lintala et al, 2007;Hanke & Hase, 2008), the plants suffered from chlorosis and reduced photosynthetic activity, which finally resulted in reduced growth. Although the level of total NADP(H) was not affected in the mutants, the NADPH/NADP + ratio was strongly reduced (Hajirezaei et al, 2002;Hald et al, 2008).…”