Ancient and essential: the assembly of iron–sulfur clusters in plants

In plants iron–sulfur (Fe–S) proteins are found in the plastids, mitochondria, cytosol and nucleus, where they are essential for numerous physiological and developmental processes. Recent mutant studies, mostly in Arabidopsis thaliana, have identified three pathways for the assembly of Fe–S clusters. The plastids harbor the SUF (sulfur mobilization) pathway and operate independently, whereas cluster assembly in the cytosol depends on the emerging CIA (cytosolic iron–sulfur cluster assembly) pathway and mitochondria. The latter organelles use the ISC (iron–sulfur cluster) assembly pathway. In all three pathways the assembly process can be divided into a first stage where S and Fe are combined on a scaffold protein, and a second stage in which the Fe–S cluster is transferred to a target protein. The second stage might involve different carrier proteins with specialized functions.