Transcriptional Profiling of the Arabidopsis Iron Deficiency Response Reveals Conserved Transition Metal Homeostasis Networks

Iron (Fe) deficiency is counteracted by a suite of responses to ensure maintenance of vital processes for which Fe is essential. Here, we report on transcriptional changes upon Fe deficiency, investigated in two Arabidopsis (Arabidopsis thaliana) accessions, Columbia (Col-0) and C24. Functional modules of the Arabidopsis Fe deficiency syndrome were inferred from clustering of Fe-responsive genes according to their coexpression. It was found that the redistribution of transition metals is an integral part of the reduction-based response to Fe starvation. The differential expression of metal transporters under the control of the FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR appeared to reflect an anticipated reaction rather than a response to the actual change in metal distribution. In contrast, the regulation of the zinc transporters ZRT/IRT-LIKE PROTEIN2 (ZIP2), ZIP3, ZIP4, and ZIP9 was dependent on the cellular zinc level, and their regulation by Fe was a secondary effect. Cellular Fe homeostasis was found to be closely coupled to Fe-related processes in the plastids. Using clustered genes as bait in gene-fishing experiments, we were able to attribute potentially important roles for gene candidates that have no previously described function in the Fe deficiency response. These results demonstrate a conceptually novel and integrative view into the regulation and interactions that allow Arabidopsis to adapt to suboptimal Fe availability.