Overview of expression control of NFS1 and NFS2 genes. This model shows some cis-elements found within the promoter regions of cysteine desulfurases genes (green and red boxes). According to our qPCR data and in silico analysis those genes have particular expression triggers, indicated above the cis-elements (blue boxes). NFS1_Chr01 is modulated by stresses, such as cold and salicylic acid (SA), and induced in roots. NFS1_Chr11 is modulated by the same stimuli but induced in leaves. NFS2_Chr09 is modulated by cold, whereas NFS2_Chr15 is modulated by the same stress and induced in leaves. In plastid (bottom), cysteine desulfurase catalyses the release of sulfur from cysteine to [Fe-S] cluster biogenesis in order to organelle request. In mitochondria (top), the same process occurs to provide clusters to the organelle and cytosol/nucleus, being stimulated by a small protein called ISD11 (light green box). An export system, including an ABC transporter, is involved in maturation of Fe-S proteins outside mitochondria. Some Fe-S proteins in cytosol and nucleus are involved in cellular sensing, controlling gene expression.