Natural allelic variation of FRO2 modulates Arabidopsis root growth under iron deficiency

Low availability of Fe significantly limits crop yields in many parts of the world. However, it is largely unknown which genes and alleles adjust plant growth in Fe limited environments. Using natural variation of a geographically restricted panel of Arabidopsis thaliana accessions, we identify allelic variation at the FRO2 locus associated with root length under iron deficiency. We show that non-coding sequence variation at the FRO2 locus leads to variation of FRO2 transcript levels, as well as ferric chelate reductase activity, and is causal for a portion of the observed root length variation. These FRO2 allele dependent differences are coupled with altered seedling phenotypes grown on iron-limited soil. Overall, we show that these natural genetic variants of FRO2 tune its expression. These variants might be useful for improvement of agronomically relevant species under specific environmental conditions, such as in podzols or calcareous soils.