The Fe-S cluster assembly NFS1-ISD11-FH subcomplex is involved in heme biosynthesis in plants

Iron is an essential micronutrient for plants, participating in vital processes such as the biogenesis of hemoproteins and iron-sulfur (Fe-S) proteins. This study investigated the functional relationship between the mitochondrial Fe-S cluster (ISC) assembly machinery and the heme synthesis pathway in Arabidopsis thaliana, specifically focusing on the NFS1-ISD11-FH subcomplex. Using cysteine desulfurase (AtNFS1) T-DNA insertion mutants and overexpression lines, it was found that non-covalently bound leaf heme content directly correlated with AtNFS1 expression, varying by roughly 30%. Furthermore, catalase activity-a heme-dependent enzyme-altered accordingly, increasing in overexpression lines and decreasing in mutants, despite no significant changes in catalase gene expression (CAT1-3). Rescue experiments in isolated mutant mitochondria demonstrated that adding hemin almost fully restored catalase activity, whereas protoporphyrin IX had no effect, confirming that heme deficiency drives the low enzymatic activity. Additionally, reducing frataxin (AtFH) expression via transient transformation decreased both heme content and catalase activity, showing an additive negative effect when combined with reduced AtNFS1. In conclusion, this work demonstrates a clear functional connection between the ISC machinery and heme biosynthesis. The NFS1-ISD11-FH subcomplex would facilitate the production of heme groups required for active hemoproteins, with frataxin playing a crucial role, possibly through its ferrochelatase activity enhanced by the complex.