Genetic basis of historical pea mutants that hyper-accumulate iron

The Pisum sativum (pea) mutants degenerate leaves ( dgl ) and bronze ( brz ) accumulate large amounts of iron in leaves. First described several decades ago, the two mutants have provided important insights into iron homeostasis in plants but the underlying mutations have remained unknown. Using exome sequencing we identified an in-frame deletion associated with dgl in a BRUTUS homologue. The deletion is absent from wild type and the original parent line. BRUTUS belongs to a small family of E3 ubiquitin ligases acting as negative regulators of iron uptake in plants. The brz mutation was previously mapped to chromosome 4, and superimposing this region to the pea genome sequence uncovered a mutation in OPT3 , encoding an oligopeptide transporter with a plant-specific role in metal transport. The causal nature of the mutations was confirmed by additional genetic analyses. Identification of the mutated genes rationalises many of the previously described phenotypes and provides new insights into shoot-to-root signalling of iron deficiency. Furthermore, the non-lethal mutations in these essential genes suggest new strategies for biofortification of crops with iron. Significance statement Two iron-accumulating pea mutants first described more than 30 years ago have greatly contributed to our understanding of iron homeostasis in plants, but the mutations were never identified. Here we show that the phenotypes are caused by mutations in the BRUTUS and OPT3 genes and how this leads to specific defects in iron signalling and leaf development.