Arabidopsis AtIscA-I is affected by deficiency of Fe–S cluster biosynthetic scaffold AtCnfU-V

IscA has been proposed to be a scaffold protein of the iron–sulfur cluster biosynthetic machinery. We have identified the IscA homolog to be localized to plastids, termed AtIscA-I, in Arabidopsis thaliana. The AtIscA-I protein was apparently constitutively expressed in all tissues analyzed in Arabidopsis. The AtIscA-I protein exists in the stroma as a soluble protein which tends to form a homo-dimer and can host a [2Fe–2S]-like cluster. Complete loss of the protein from plastids did not cause any significant defect either in normal plant growth or in biogenesis of major iron–sulfur proteins, indicating this protein is not essential or redundant for these functions. In contrast, loss of one of the three plastid-localized CnfU scaffold proteins, AtCnfU-V, caused significant reduction in the level of AtIscA-I. These data suggest that efficient biogenesis of AtIscA-I scaffold requires function of another essential scaffold protein CnfU.