Elucidating the function of the CYBDOM protein HYP1 in phosphorus deficiency-dependent primary root growth
Final Report Abstract
The availability of nutrients in soils has a strong impact on root growth and development. 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 tips of P-deprived plants. Many plant species secrete malate to release P sorbed onto Fe (hydro)oxides, which not only increases the availability of P but also of Fe. However, it still remains unclear how roots counteract the increased Fe availability and redox activity. By combining transcriptomics and bioinformatics with reverse genetics in Arabidopsis thaliana, we identified a previously uncharacterized gene as critical to maintain cell elongation and meristem integrity under low-P conditions. The identified gene encodes for a CYBDOM, consisting of a plasma membrane-embedded cytochrome b561 domain fused to an apoplastic dopamine ß-monooxygenase N-terminal (DOMON) domain. Due to the more severe loss of meristematic integrity and more significantly inhibited cell elongation of a T-DNA insertional mutant specifically under low-P conditions, we named the gene HYPERSENSITIVE TO LOW P1 (HYP1). HYP1 is up-regulated in response to P deficiency in the proximal zone of the root apical meristem and the protein locates in the plasma membrane. AlphaFoldsupported modelling identified two putative coordination sites for b-hemes in the cytochrome b561 domain and one additional site in the DOMON. We further demonstrated that HYP1 mediates ascorbate-dependent trans-plasma membrane electron transport in Xenopus laevis oocytes and reduces ferric and cupric substrates in planta, suggesting that HYP1 is a metalloreductase. Disruption of HYP1 resulted in increased Fe and callose accumulation in the root meristem and significant transcriptional changes in roots. In contrast, HYP1 overexpression prevented Fe overaccumulation, aberrant callose deposition and meristem disintegration, thereby improving root growth under low-P conditions. Using a cell type-specific complementation approach, it was possible to determine that HYP1 activity in a confined zone of the root apical meristem is required to maintain meristem integrity and root growth. In this root portion, HYP1 promoted the depletion of apoplastic Fe pools solubilized by low P-induced malate release. Altogether, our study uncovered an ascorbate-dependent metalloreductase that protects root meristems of P-deficient plants from increased Fe availability and provided insights into the physiological function of the yet poorly characterized but ubiquitous CYBDOM proteins.
Publications
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Ferric reduction by a CYBDOM protein counteracts increased iron availability in root meristems induced by phosphorus deficiency. Nature Communications, 15(1).
Maniero, Rodolfo A.; Picco, Cristiana; Hartmann, Anja; Engelberger, Felipe; Gradogna, Antonella; Scholz-Starke, Joachim; Melzer, Michael; Künze, Georg; Carpaneto, Armando; von Wirén, Nicolaus & Giehl, Ricardo F. H.
