The PAP/SAL1 retrograde signaling pathways is involved in iron homeostasis via ethylene activity in Arabidopsis.

BALPARDA, MANUEL; DIEGO FABIAN GOMEZ CASATI; PAGANI M.A.

Salta

Congreso; LV Reunión de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB),; 2019

SAIB

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