Background: Under limited iron (Fe) availability maize, a Strategy II plant, improves Fe acquisition through the
release of phytosiderophores (PS) into the rhizosphere and the subsequent uptake of Fe-PS complexes into root
cells. Occurrence of Strategy-I-like components and interactions with phosphorous (P) nutrition has been
hypothesized based on molecular and physiological studies in grasses.
Results: In this report transcriptomic analysis (NimbleGen microarray) of Fe deficiency response revealed that maize
roots modulated the expression levels of 724 genes (508 up- and 216 down-regulated, respectively). As expected,
roots of Fe-deficient maize plants overexpressed genes involved in the synthesis and release of 2’-deoxymugineic
acid (the main PS released by maize roots). A strong modulation of genes involved in regulatory aspects, Fe
translocation, root morphological modification, primary metabolic pathways and hormonal metabolism was
induced by the nutritional stress. Genes encoding transporters for Fe2+ (ZmNRAMP1) and P (ZmPHT1;7 and ZmPHO1)
were also up-regulated under Fe deficiency.
Fe-deficient maize plants accumulated higher amounts of P than the Fe-sufficient ones, both in roots and shoots. The
supply of 1 μM 59Fe, as soluble (Fe-Citrate and Fe-PS) or sparingly soluble (Ferrihydrite) sources to deficient plants, caused a
rapid down-regulation of genes coding for PS and Fe(III)-PS transport, as well as of ZmNRAMP1 and ZmPHT1;7.
Levels of 32P absorption essentially followed the rates of 59Fe uptake in Fe-deficient plants during Fe resupply, suggesting
that P accumulation might be regulated by Fe uptake in maize plants.
Conclusions: The transcriptional response to Fe-deficiency in maize roots confirmed the modulation of known genes
involved in the Strategy II and revealed the presence of Strategy I components usually described in dicots. Moreover, data
here presented provide evidence of a close relationship between two essential nutrients for plants, Fe and P, and highlight
a key role played by Fe and P transporters to preserve the homeostasis of these two nutrients in maize plants.
