AUTHOR=Ramamurthy Raghuprakash Kastoori , Waters Brian M. 

TITLE=Mapping and Characterization of the fefe Gene That Controls Iron Uptake in Melon (Cucumis melo L.)

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01003

DOI=10.3389/fpls.2017.01003

ISSN=1664-462X

ABSTRACT=<p>Iron (Fe) deficiency in plants limits crop growth and productivity. Molecular mechanisms that plants use to sense and respond to Fe deficiency by coordinated expression of Fe-uptake genes are not fully understood. The C940-fe chlorotic melon (<italic>Cucumis melo</italic>) mutant known as <italic>fefe</italic> is unable to upregulate Fe-uptake genes, however, the <italic>FeFe</italic> gene had not been identified. In this study, we used two F<sub>2</sub> mapping populations to map and identify the <italic>FeFe</italic> gene as <italic>bHLH38</italic>, a homolog of subgroup Ib <italic>bHLH</italic> genes from <italic>Arabidopsis thaliana</italic> that are involved in transcriptional regulation of Fe-uptake genes in partnership with the <italic>FIT</italic> gene. A Ty1-copia type retrotransposon insertion of 5.056 kb within <italic>bHLH38</italic> is responsible for the defect in <italic>bHLH38</italic> in <italic>fefe</italic>, based on sequencing and expression analysis. This retrotransposon insertion results in multiple non-functional transcripts expected to result in an altered and truncated protein sequence. Hairy root transformation of <italic>fefe</italic> plants using wild-type <italic>bHLH38</italic> resulted in functional complementation of the chlorotic <italic>fefe</italic> phenotype. Using a yeast-2-hybrid assay, the transcription factor Fit interacted with the wild-type bHLH38 protein, but did not interact with the <italic>fefe</italic> bHLH38 protein, suggesting that heterodimer formation of Fit/bHLH38 to regulate Fe-uptake genes does not occur in <italic>fefe</italic> roots. The second subgroup Ib <italic>bHLH</italic> gene in the melon genome is not functionally redundant to <italic>bHLH38</italic>, in contrast to Arabidopsis where four subgroup Ib <italic>bHLH</italic> genes are functionally redundant. Whereas the Arabidopsis <italic>bHLH</italic> transcript levels are upregulated by Fe deficiency, melon <italic>bHLH38</italic> was not regulated at the transcript level. Thus, the <italic>fefe</italic> mutant may provide a platform for studying <italic>bHLH38</italic> genes and proteins from other plant species.</p>