Ethylene involvement in the regulation of the H+-ATPase CsHA1 gene and of the new isolated ferric reductase CsFRO1 and iron transporter CsIRT1 genes in cucumber plants

In previous works using ethylene inhibitors and precursors, it has been shown that ethylene participates in the regulation of several Fe deficiency stress responses by Strategy I plants, such as enhanced ferric reductase activity, rhizosphere acidification and subapical root hair development. Furthermore, recent evidence suggests that ethylene could regulate the expression of both the ferric reductase and the iron transporter genes of Strategy I plants by affecting the FER (or FER-like) transcription factor. Recently, two H+-ATPase genes have been isolated from cucumber roots, CsHA1 and CsHA2. CsHA1 is up-regulated under Fe deficiency while CsHA2 is constitutively expressed. In this work we have cloned and characterized the sequences of the ferric reductase (CsFRO1) and the iron transporter (CsIRT1) genes from cucumber (Cucumis sativus L. cv Ashley). Expression of CsHA1, CsFRO1 and CsIRT1 is diminished in Fe-deficient roots by treatment with ethylene inhibitors, like Co (cobalt) or AOA (aminooxyacetic acid). Treatment with ethylene precursors, like ACC (1-aminocyclopropane-1-carboxylic acid) or Ethephon (2-chloroethylphosphonic acid), resulted in increased CsHA1, CsFRO1 and CsIRT1 transcript levels and increased ferric reductase activity during early stages of Fe deficiency. These results suggest that ethylene is involved in the regulation of CsHA1, CsFRO1 and CsIRT1 gene expression.