The universally conserved HCF101 protein is involved in assembly of [4Fe‐4S]‐cluster‐containing complexes in Arabidopsis thaliana chloroplasts

Abstract

SummaryThe seedling-lethal nuclear Arabidopsis hcf101 (high chlorophyll¯uorescence) mutant is impaired in photosynthesis and complemented by the wild-type HCF101 cDNA. Photosystem I (PSI) activity is abolished, and PSI core complexes fail to accumulate in hcf101, whereas levels of other thylakoid membrane proteins are unaffected. Northern and in vivo labelling analyses as well as studies on polysome loading show that PSI transcript levels and translation rates of proteins, which belong to PSI, are normal in hcf101. PSI-speci®c uorescence at 77 K is shifted from 735 to 728 nm in hcf101, indicating that exitons cannot ef®ciently be transferred to the PSI reaction centre, whereby the PSI antenna is almost unaffected. Mutant plants not only fail to accumulate mature PSI, which contains three [4Fe-4S] clusters (FSCs), but also are characterized by reduced levels of the soluble FSC-containing complex ferredoxin-thioredoxin reductase (FTR) in the stroma. Inhibited FTR maturation is not a secondary effect stemming from lack of PSI because the mutant hcf145, which also lacks PSI, accumulates FTR at normal levels. Levels of the [2Fe-2S] clustercontaining soluble and membrane proteins, ferredoxin and PetC, respectively, were unchanged in hcf101 plants. These data suggest a speci®c role of HCF101 in FSC biogenesis. HCF101 is plastid localized and belongs to an ancient and universally conserved family of P-loop ATPases previously designated as thè MRP' (metG related protein) family. The function identi®ed for HCF101 suggests a new designation, FSC, for this family.

Chloroplast iron-sulfur cluster protein maturation requires the essential cysteine desulfurase CpNifS

“…The altered chloroplast ultrastructure observed in CpNifSsilenced lines is reminiscent of the ultrastructure reported for an APO1 mutant (22) that affects PSI accumulation, as well as a mutant in Hcf101 and other mutations that affect PSI (23,24). Therefore, the dilated stromal lamellae and absence of grana may be a consequence of a lack of PSI.…”

AtNAP1 Represents an Atypical SufB Protein in Arabidopsis Plastids

“…In plants, NIF (17)(18)(19), HCF101 (20), and NFU proteins (35) have been shown to be involved in Fe-S assembly and we recently suggested that Arabidopsis most probably also contains a complete plastid-localized SUF system (23). In support of this notion we have demonstrated that the essential ABC/ATPase AtNAP7 can restore growth defects in a SufCdeficient E. coli mutant demonstrating that Arabidopsis harbors an evolutionary conserved SufC protein (23).…”

“…Moreover, the recent observation that Arabidopsis harbors chloroplast-localized Nif proteins AtCpNIFS/AtNFS2, AtCnfU-V, and AtCnfU-IVb (17)(18)(19) and HCF101 (20) demonstrates that plant Fe-S cluster biogenesis occurs in both mitochondria and plastids. In chloroplasts Fe-S clusters are required for cytochrome b 6 /f complex, ferredoxin and photosystem I ensuring electron flow in the thylakoids (21,22); however, to date Fe-S cluster biogenesis in plastid is poorly understood.…”

Interaction with Cfd1 Increases the Kinetic Lability of FeS on the Nbp35 Scaffold

“…Members of the ApbC/Nbp35 family are widely distributed, being found in virtually all organisms in the biosphere (17,20,22). Intriguingly, the requirement for two such P-loop NTPases within the same pathway for FeS cluster biogenesis to date has only been demonstrated in animals and fungi (23).…”