Unravelling the regulatory function of FurA in Anabaena sp. PCC 7120 through 2-D DIGE proteomic analysis.

The Anabaena sp. PCC 7120 ferric uptake regulator FurA controls iron homeostasis and appears implicated in a broad regulatory network, whereas failures to eliminate wild-type copies of furA gene from the polyploid genome suggest essential functions. In the present study, we comparatively analyzed the proteomes of a furA-overexpressing strain and its parental wild-type in conjunction with subsequent semi-quantitative RT-PCR and electrophoretic mobility shift assays, in order to identify direct transcriptional targets and unravel new biological roles of FurA. The results of such approach drove us to find 10 novel direct targets belonging to different functional categories including photosynthesis, energy metabolism, oxidative stress defences, redox regulation, signal transduction mechanisms, DNA replication, thiamine biosynthesis and heterocyst differentiation. Two peroxiredoxins and the thioredoxin reductase exhibited the most significant changes in both mRNA level and protein abundance under a FurA overexpression background, indicating a connection between iron metabolism, redox signalling and oxidative stress defences. A FurA box consensus sequence was ill-defined. The results suggest that particular DNA structures rather than a defined sequence govern FurA regulation of its target genes. Overall, the results provide new insights into the FurA regulon in Anabaena sp. PCC 7120.