TheSUFBC₂D complex is required for the biogenesis of all major classes of plastid Fe‐S proteins

Abstract

SUMMARYIron-sulfur (Fe-S) proteins play crucial roles in plastids, participating in photosynthesis and other metabolic pathways. Fe-S clusters are thought to be assembled on a scaffold complex composed of SUFB, SUFC and SUFD proteins. However, several additional proteins provide putative scaffold functions in plastids, and, therefore, the contribution of SUFB, C and D proteins to overall Fe-S assembly still remains unclear. In order to gain insights regarding Fe-S cluster biosynthesis in plastids, we analyzed the complex composed of SUFB, C and D in Arabidopsis by blue native-polyacrylamide gel electrophoresis. Using this approach, a major complex of 170 kDa containing all subunits was detected, indicating that these proteins constitute a SUFBC 2 D complex similar to their well characterized bacterial counterparts. The functional effects of SUFB, SUFC or SUFD depletion were analyzed using an inducible RNAi silencing system to specifically target the aforementioned components; resulting in a decrease of various plastidic Fe-S proteins including the PsaA/B and PsaC subunits of photosystem I, ferredoxin and glutamine oxoglutarate aminotransferase. In contrast, the knockout of potential Fe-S scaffold proteins, NFU2 and HCF101, resulted in a specific decrease in the PsaA/B and PsaC levels. These results indicate that the functions of SUFB, SUFC and SUFD for Fe-S cluster biosynthesis cannot be replaced by other scaffold proteins and that SUFBC 2 D, NFU2 and HCF101 are involved in the same pathway for the biogenesis of PSI. Taken together, our results provide in vivo evidence supporting the hypothesis that SUFBC 2 D is the major, and possibly sole scaffold in plastids.

A Program for Iron Economy during Deficiency Targets Specific Fe Proteins

“…1, 3, and 4). RNAi lines induced for loss of NFS2 or SufBCD complex components had shown a general loss of all Fe-S proteins, including strong effects on PSI subunits PSAA, and PSAB on GOGAT (Van Hoewyk et al, 2007;Hu et al, 2017b). However, we did not see this general loss of plastid Fe-S cluster proteins for Fe deficiency.…”

“…However, we did not see this general loss of plastid Fe-S cluster proteins for Fe deficiency. Conversely, whereas we noted down-regulation of the heme containing subunits of the cytochrome-b 6 f subunits together with PETC (Rieske protein) in Fe deficiency, the genetically induced loss of SUFB, SUFC, or SUFD strongly affected Rieske protein but had marginal effects on CYTb 6 and CYTf protein accumulation (Hu et al, 2017b).…”

“…Therefore, at least some of the observed effects seem to be caused by Fe deficiency proper and not just by downstream defects due to lack of cofactor assembly. We can also compare consequences of Fe deficiency at the molecular level with effects caused by genetically induced loss of Fe-S assembly factors NFS2 (Van Hoewyk et al, 2007) and SUF-BCD (Hu et al, 2017a(Hu et al, , 2017b. Loss via RNAi of NFS2 activity (Van Hoewyk et al, 2007) or SUF-BCD activity (Hu et al, 2017b) caused physiological effects after 1 week that are very similar to the Fe deficiency described here (Figs.…”

“…SUFB is a key component of the plastid SUF-BCD complex that functions as a scaffold required for the assembly of all plastid Fe-S clusters (Hu et al, 2017b). Down-regulation of SUFB in Fe deficiency had been reported but only at the transcript level, both in Arabidopsis grown on agar media (Xu et al, 2005;Sivitz et al, 2012;Rodríguez-Celma et al, 2013) and in rice (Oryza sativa; Liang et al, 2014).…”

Roles and maturation of iron–sulfur proteins in plastids

“…1) [14]. The assembly of a Fe–S cluster on this scaffold complex theoretically requires the concerted action of several proteins as it requires the polypeptide backbones, ATP, Fe, and sulfur atoms and electrons.…”