CONICET | Buscador de Institutos y Recursos Humanos

PAP accumulates in Arabidopsis thaliana plastids in response to high light or drought stress and is able to regulate stress-responsive nuclear genes. Its levels are controlled by dephosphorylation to AMP through SAL1 enzyme activity. The mode of action of PAP is the inhibition of 5´ to 3´ exoribonucleases (XRNs). Transcriptome analysis of Arabidopsis sal1 and xrn mutant plants further revealed that the ferritin genes AtFer1, AtFer3, and AtFer4 are upregulated in these genetic backgrounds, thus establishing a link between the PAP retrograde signaling pathway and the regulation of iron (Fe) homeostasis genes. In this study, we used three different mutants of the PAP/SAL1 retrograde pathway to characterize the relation of this retrograde signaling pathway with Fe metabolism. Mutant plants showed an increment in the expression level of genes implicated in Fe uptake and storage. Also, mutant lines accumulated more Fe content in shoots, roots and seeds than wild type plants when they grew in both Fe-sufficient and Fe-deficient media. Likewise, mutant plant roots did not deactivated Fe uptake when foliar Fe was applied. As reported, AtERF1 -a transcription factor of the ethylene signaling pathway- is a target of XRN4 degradation in a posttranscriptional regulation process. In PAP/SAL1 mutant lines, there was an increment in AtEFR1 and Fe uptake transcripts. However in the presence of ethylene inhibitors, mutant lines presented a reduction in the relative expression of genes involved in Fe acquisition and in the ferrochelate reductase activity. Furthermore, RNA decay assays showed that full XRN4 activity restored AtFRO2 and AtIRT1 transcripts (Strategy I genes of Fe uptake) up to wild type line levels in RNA extracts of PAP/SAL1 mutants. In summary, through these results we can infer that there is a link between PAP/SAL pathway, ethylene signaling and Fe metabolism.