Elucidating the function of the CYBDOM protein HYP1 in phosphorus deficiency-dependent primary root growth

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The availability of nutrients in soils has a strong impact on root growth and development. Apart from effects triggered by single nutrients, also the interaction of different elements can act as a cue to modify root developmental processes. Recent studies have shown that the transition metal iron (Fe) can inhibit root elongation in response to low phosphorus (P) by initiating a complex interplay of redox reactions and signaling events in the root apical zone of P-deprived plants. However, still little is known about the mechanism underlying Fe-dependent redox activity in P-deficient roots. By combining transcriptomics with bioinformatics and reverse genetics in Arabidopsis thaliana we identified a novel cytochrome b561/dopamine beta-monooxygenase N-terminal (CYBDOM) protein, which is predicted to drive apoplastic redox reactions by using cytosolic ascorbate as an electron donor. Our preliminary work demonstrated that the identified protein, which we named HYPERSENSITIVE TO LOW P 1 (HYP1), is crucial for maintaining root growth on low P availability. Thus, the main objectives of this project are: i) to determine the genetic link between HYP1 and other molecular players that adjust root growth under low P and to assess how HYP1 localization in specific roots zones affects cell biological responses in zones where this protein is not expressed; ii) to characterize HYP1- and ascorbate-dependent redox changes in P-deprived roots and to investigate the role of HYP1 in ferric Fe reduction or ascorbate regeneration in the apoplast; and iii) to determine the biochemical function of HYP1 and the functional interplay between the protein’s cytochrome b561 core and the DOMON domain. To achieve these goals, we will combine genetic tools with histochemical, cell biological, biochemical and pharmacological methods. The findings of this research will shed light on the physiological function of yet poorly characterized ascorbate-dependent trans-membrane electron transport via CYBDOMs. Furthermore, the characterization of HYP1 will provide a means to improve root stress tolerance by manipulating root apoplastic redox activity.