An Fe Deficiency Responsive Element with a Core Sequence of TGGCA Regulates the Expression of FEA1 in Chlamydomonas reinharditii

Iron is essential to the unicellular green alga Chlamydomonas, but the molecular mechanism for response to iron deficiency remains largely unknown. In previous studies, we have identified FOX1 and ATX1 FEREs (Fe deficiency-responsive elements) as important regulation components of iron response in this organism. Here we present another iron regulated gene FEA1, which promoter was analysed by using a 5'- and 3'-end deletion and a scanning mutagenesis assay. The results reveal that the co-existence of -273/-188 and -118/-49 regions from transcriptional start site of FEA1 were sufficient and necessary for Fe deficiency-induced expression. Further deletion analysis indicates both -273/-253 and -103/-85 regions are essential for inducible expression. The scanning mutagenesis analysis of these regions identifies two cis-acting elements: the FeaFeRE1 at -273/-259 (CTGCGGTGGCAAAGT) and FeaFeRE2 at -106/-85 (CCGCCGCNNNTGGCACCAGCCT). Sequence comparison of FeaFeRE1 and FeaFeRE2 reveals a core sequence of TGGCA, which had been found in our previously reported Fe-deficiency-inducible gene ATX1. Moreover, we show that the promoter region of several genes, including FRE1, IRT1, ISCA, ZRT1, ZRT5, NRAMP2 and COPT1, also contains this core sequence, suggesting that at least two classes FeRE elements exist in Clamydomonas, one in FEA1 and ATX1 and others the second in FOX1, FEA2, MTP4, NRAMP3 and RBOL1.