Ferric reduction by a CYBDOM protein counteracts increased iron availability in root meristems induced by phosphorus deficiency

The Phosphorus-Iron Nexus: Decoding the Nutrients Interaction in Soil and Plant

Phosphorus (P) and iron (Fe) are two essential mineral nutrients in plant growth. It is widely observed that interactions of P and Fe could influence their availability in soils and affect their homeostasis in plants, which has received significant attention in recent years. This review presents a summary of latest advances in the activation of insoluble Fe-P complexes by soil properties, microorganisms, and plants. Furthermore, we elucidate the physiological and molecular mechanisms underlying how plants adapt to Fe-P interactions. This review also discusses the current limitations and presents potential avenues for promoting sustainable agriculture through the optimization of P and Fe utilization efficiency in crops.

Recent advances in research on phosphate starvation signaling in plants

Phosphorus is indispensable for plant growth and development, with its status crucial for determining crop productivity. Plants have evolved various biochemical, morphological, and developmental responses to thrive under conditions of low P availability, as inorganic phosphate (Pi), the primary form of P uptake, is often insoluble in soils. Over the past 25 years, extensive research has focused on understanding these responses, collectively forming the Pi starvation response system. This effort has not only expanded our knowledge of strategies to cope with Pi starvation (PS) but also confirmed their adaptive significance. Moreover, it has identified and characterized numerous components of the intricate regulatory network governing P homeostasis. This review emphasizes recent advances in PS signaling, particularly highlighting the physiological importance of local PS signaling in inhibiting primary root growth and uncovering the role of TORC1 signaling in this process. Additionally, advancements in understanding shoot-root Pi allocation and a novel technique for studying Pi distribution in plants are discussed. Furthermore, emerging data on the regulation of plant-microorganism interactions by the PS regulatory system, crosstalk between the signaling pathways of phosphate starvation, phytohormones and immunity, and recent studies on natural variation in Pi homeostasis are addressed.

A CYBDOM protein impacts iron homeostasis and primary root growth under phosphate deficiency in Arabidopsis

Arabidopsis primary root growth response to phosphate (Pi) deficiency is mainly controlled by changes in apoplastic iron (Fe). Upon Pi deficiency, apoplastic Fe deposition in the root apical meristem activates pathways leading to the arrest of meristem maintenance and inhibition of cell elongation. Here, we report that a member of the uncharacterized cytochrome b561 and DOMON domain (CYBDOM) protein family, named CRR, promotes iron reduction in an ascorbate-dependent manner and controls apoplastic iron deposition. Under low Pi, the crr mutant shows an enhanced reduction of primary root growth associated with increased apoplastic Fe in the root meristem and a reduction in meristematic cell division. Conversely, CRR overexpression abolishes apoplastic Fe deposition rendering primary root growth insensitive to low Pi. The crr single mutant and crr hyp1 double mutant, harboring a null allele in another member of the CYDOM family, shows increased tolerance to high-Fe stress upon germination and seedling growth. Conversely, CRR overexpression is associated with increased uptake and translocation of Fe to the shoot and results in plants highly sensitive to Fe excess. Our results identify a ferric reductase implicated in Fe homeostasis and developmental responses to abiotic stress, and reveal a biological role for CYBDOM proteins in plants.