FdC1 and Leaf-Type Ferredoxins Channel Electrons From Photosystem I to Different Downstream Electron Acceptors

Abstract

Plant-type ferredoxins in Arabidopsis transfer electrons from the photosystem I to multiple redox-driven enzymes involved in the assimilation of carbon, nitrogen, and sulfur. Leaf-type ferredoxins also modulate the switch between the linear and cyclic electron routes of the photosystems. Recently, two novel ferredoxin homologs with extra C-termini were identified in the Arabidopsis genome (AtFdC1, AT4G14890; AtFdC2, AT1G32550). FdC1 was considered as an alternative electron acceptor of PSI under extreme ferredoxin-deficient conditions. Here, we showed that FdC1 could interact with some, but not all, electron acceptors of leaf-type Fds, including the ferredoxin-thioredoxin reductase (FTR), sulfite reductase (SiR), and nitrite reductase (NiR). Photoreduction assay on cytochrome c and enzyme assays confirmed its capability to receive electrons from PSI and donate electrons to the Fd-dependent SiR and NiR but not to the ferredoxin-NADP+ oxidoreductase (FNR). Hence, FdC1 and leaf-type Fds may play differential roles by channeling electrons from photosystem I to different downstream electron acceptors in photosynthetic tissues. In addition, the median redox potential of FdC1 may allow it to receive electrons from FNR in non-photosynthetic plastids.

Primary leaf‐type ferredoxin 1 participates in photosynthetic electron transport and carbon assimilation in rice

“…The 2Fe–2S iron–sulfur cluster binding proteins are necessary for photosynthetic electron transport in algae and Arabidopsis (Hanke et al ., 2004a; Hanke and Mulo, 2013; Guan et al ., 2018). The specific functions of different Fds in rice are not fully understood, however.…”

“…In photosynthetic tissues, AtFdC1 transports photosynthetic electrons from PSI to NiR and SiR in nitrogen and sulfur assimilation, respectively. In non‐photosynthetic tissues, the median redox potential of AtFdC1 may allow it to receive electrons from FNR (Guan et al ., 2018).…”

“…To measure the electron transfer from PSI to Fd1, FdC2 and ΔFd1 proteins, the photoreduced cytochrome c assay was carried out as described previously (Voss et al ., 2011; Guan et al ., 2018). A reaction mixture with a total volume of 0.2 ml, containing 10 mg L −1 thylakoid membrane, 1 m m MgCl 2 , 0.1 m NaCl, 0.025 m HEPES‐KOH (pH 7.6), 0.2 m m cytochrome c and various concentrations of recombinant Fd1, FdC2, ΔFd1‐1, ΔFd1‐2 or ΔFd1‐3 (0–4 µ m ) proteins, was illuminated under LEDs with a photon intensity of 300 μmol m −2 sec −1 .…”

An alternative plant-like cyanobacterial ferredoxin with unprecedented structural and functional properties

“…This process was measured via cytochrome c reduction (by Fd red ) under continuous illumination and a 14-fold decrease in the Michaelis constant K m was found vs the main Fd. FdC1 has a relatively high midpoint potential (-281 mV, ibid) and may not be primarily expressed in leaves [94], which would be in line with its poor reactivity with PSI. In a different approach, site-directed mutants of FdN studied with a low time resolution [95] showed that the effects of mutations are much smaller when looking at reduction by PSI than when looking at reduction of FNR by Fd red , concluding that Fd reduction by PSI is relatively robust toward amino-acid substitutions.…”

“…In Arabidopsis, it was found that the minor ferredoxin FdC1 is unable to photoreduce NADP + via FNR, and this absence of activity was attributed to its high midpoint potential [93]. FdC1 can however interact with leaf-type electron acceptors including NiR, as with PSI, and can interact with FNR for reverse electron flow, albeit with a decreased efficiency [94]. The same authors showed that FdC1 might divert some reducing power away from FNR in Arabidopsis mutants overexpressing this Fd.…”