L-DOPA elicits iron deficiency response through root-to-shoot signaling and independently of the canonical regulatory pathway.

Iron (Fe) deficiency causes anemia in humans and yield losses in crops. Increasing Fe concentration in plants would be beneficial for agriculture and global health. The allelochemical L-3-(3,4-dihydroxyphenyl)alanine (L-DOPA) can promote Fe accumulation, and its potential use for Fe biofortification was investigated. L-DOPA was exogenously supplied to Arabidopsis thaliana, and the expression of Fe deficiency genes was measured in shoots and roots of the ima8x and bhlh121 mutants defective in Fe deficiency response. L-DOPA and Fe were quantified, and Fe was imaged in leaves. L-DOPA triggers a transient and intense increase in the expression of Fe deficiency genes, leading to Fe accumulation in shoots. The transcription of Fe deficiency genes was also induced in shoots, indicating that L-DOPA affected Fe perception by leaves. Surprisingly, while L-DOPA accumulated in roots, it remained undetectable in shoots. The increased expression of the upstream Fe deficiency genes upon L-DOPA exposure did not require functional URI/bHLH121 nor IMA genes and also occurred in rice. L-DOPA stimulated the transcriptional response to Fe deficiency through a mechanism independent of the well-known network of BASIC HELIX-LOOP-HELIX transcription factors that regulate Fe homeostasis. This process involved a root-borne signal that activated the shoot response to Fe deficiency in Fe-overloaded plants.