In regulation of Fe uptake genes and was first

In Arabidopsis
thaliana, genes involved in the Fe deficiency response can be grouped into sub-clusters.
Genes involved in Fe uptake and transport, that are directly or indirectly
dependent on the major regulator of Strategy I, FIT, are grouped into the so called
“FIT target network” and contains root-expressed genes like IRT1 (Colangelo and Guerinot, 2004; Ivanov et al., 2012;
Mai et al., 2016). An
additional cluster contains FIT-independent genes, such as PYE and its direct targets as well as BHLH039 and BHLH101. As associated
genes function mainly in Fe homeostasis, this sub-cluster can be referred to as
“Fe homeostasis network”, (Ivanov et al., 2012).

 

1.1.1       
Regulation
of Fe Deficiency Response by the FIT Target Network

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The Fe regulated, root specific bHLH transcription
factor FER is responsible for the transcriptional regulation of Fe uptake genes
and was first identified in Solanum
lycopersicum (Ling et al., 2002; Brumbarova and Bauer, 2005). The FIT gene encodes the respective FER homolog
in Arabidopsis (Bauer et al., 2004; Colangelo and Guerinot, 2004;
Jakoby et al., 2004; Yuan et al., 2005). FIT promotor activity was detected in
epidermal cells within the differentiation
zone and elongation zone of the main root, in lateral roots, as well as
in the central cylinder. fit1-1 loss-of-function
causes lethality if not supplemented with Fe. (Colangelo and Guerinot, 2004). FIT
regulates the expression of 72 out of 179 Fe-responsive genes (Colangelo and Guerinot, 2004). Interestingly, recently 13 novel genes
were identified, being strictly Fe-dependent and FIT-regulated (Mai et al., 2016). Within these 85 genes, genes involved in Fe uptake,
like IRT1, ABCG37 or F6’H1, but in
Fe homeostasis, e.g. natural
resistance-associated macrophage protein1 (NRAMP1), NICOTIANAMINE
SYNTHASE1 (NAS1) or ZRT/IRT-LIKE PROTEIN8 (ZIP8)
are present (Colangelo and
Guerinot, 2004; Mai et al., 2016).