Biology subjects

Castillo-Michel, H.

Publications and source records attributed to Castillo-Michel, H..

5 recordsLinked to original sources

bioRxiv2026

Medicago truncatula Iron-chaperone 1 (ICHAP1) is required for symbiotic nitrogen fixation

Hundreds of proteins in the cell require iron (Fe) or Fe-containing cofactors to function. However, how Fe2+ or Fe3+ are specifically allocated to each of these proteins in plant cells remains largely unknown. It has been proposed that Fe metalation could be driven by specific interactions with Fe-shuttling proteins known as Fe-chaperones. Here, we present the first family of plant Fe2+-chaperones (ICHAPs) with orthologues in dicots and monocots. The role of these proteins in Fe distribution to Fe-dependent metabolic processes has been illustrated using symbiotic nitrogen fixation in Medicago truncatula root nodules. ICHAP1 is a soluble Fe2+-binding protein that interacts with plasma membrane Fe2+ transporter NRAMP1, but not with symbiosome Fe2+-transporters. ICHAP1 mutants present altered Fe distribution in cells and they cannot fix nitrogen. A second family member, ICHAP2 is required to target Fe2+ to symbiosomes, as it accepts Fe2+ from ICHAP1 and interacts with symbiosome Fe2+-importer VTL8, but not with NRAMP1. These results indicate a path for Fe2+ allocation from the plasma membrane to the symbiosome through specific protein-protein interactions and Fe2+ exchange from NRAMP1 to ICHAP1, to ICHAP2, and to VTL8.

plant biology↗

bioRxiv2026

NRAMP2 controls manganese partitioning between seed coat and embryo to regulate seed vigor

Seed development and germination depend on the coordinated transport of macronutrients and micronutrients, which sustain the embryo and determine seed vigour. Manganese (Mn) is an essential micronutrient involved in various metabolic processes, yet its role in seed development is not well understood. In this study, we investigated manganese (Mn) homeostasis in seeds and identified NRAMP2, a previously characterised trans-Golgi-localised Mn exporter, as a key transporter that controls Mn delivery to the embryo. Promoter analysis showed NRAMP2 expression in the chalazal region, which is a central hub for the exchange of nutrients between maternal tissues and the developing seed. X-ray fluorescence mapping revealed mislocalisation of Mn in nramp2 mutant seeds, retention of Mn on the seed coat and markedly reduced levels of Mn in the embryo. Functionally, Mn depletion delayed seed germination and increased physiological dormancy by reducing reactive oxygen species (ROS) accumulation. Our results uncover the vital role of Mn in supporting embryo development and seed vigour, establishing NRAMP2 as a pivotal component of the Mn transport machinery during seed development.

plant biology↗

bioRxiv2025

Synchrotron XRF imaging reveals manganese accumulation in the Golgi and post-synapses of neurons and enhanced uptake in astrocytes

Manganese is an essential trace metal for humans, but excessive exposure can cause neurotoxicity, including parkinsonian syndromes, cognitive deficits, and has also been implicated in the pathogenesis of neurodegenerative diseases. Globally, tens of millions of people are exposed to elevated manganese levels through drinking water, exceeding the WHO recommended guideline. Despite its public health significance, the cellular and subcellular mechanisms underlying manganese neurotoxicity remain poorly defined, particularly its distribution across brain cell types and its specific intracellular targets. In this study, we investigated manganese accumulation in primary cultures of hippocampal neurons and astrocytes. Using a correlative imaging approach that combined cryo-fluorescence light microscopy with synchrotron X-ray fluorescence imaging, we mapped and quantified manganese at subcellular resolution. Our analysis revealed that manganese preferentially accumulates in the Golgi apparatus of both neurons and astrocytes. In neurons, manganese was also detected in dendrites at the postsynaptic density, suggesting a role in synaptic vulnerability. Quantitative elemental analysis showed that astrocytes accumulated 3 times more manganese than neurons. Furthermore, when neurons were co-cultured with astrocytes, their manganese uptake was significantly reduced, indicating a possible protective or buffering role of astrocytes. These findings identify key cellular and subcellular targets of manganese and highlight the Golgi apparatus as a major regulator of manganese neurotoxicity. This work provides a foundation for understanding cell type-specific responses to manganese exposure and may inform the development of targeted neuroprotection strategies. Significance statementManganese neurotoxicity impact millions of people worldwide. Understanding how manganese distributes within brain cells is critical for addressing its neurotoxic effects. This study identifies the Golgi apparatus and postsynaptic density as key sites of manganese accumulation and reveals astrocytes as major regulators of neuronal manganese uptake. These findings provide a cellular framework for developing targeted strategies to mitigate manganese-induced neurotoxicity.

neuroscience↗

bioRxiv2019

Nicotianamine synthase 2 is required for symbiotic nitrogen fixation in Medicago truncatula nodules

Symbiotic nitrogen fixation carried out by the interaction between legumes and diazotrophic bacteria known as rhizobia requires of relatively large levels of transition metals. These elements act as cofactors of many key enzymes involved in this process. Metallic micronutrients are obtained from soil by the roots and directed to sink organs by the vasculature, in a process participated by a number of metal transporters and small organic molecules that mediate metal delivery in the plant fluids. Among the later, nicotianamine is one of the most important. Synthesized by nicotianamine synthases (NAS), this non-proteinogenic amino acid forms metal complexes participating in intracellular metal homeostasis and long-distance metal trafficking. Here we characterized the NAS2 gene from model legume Medicago truncatula. MtNAS2 is located in the root vasculature and in all nodule tissues in the infection and fixation zones. Symbiotic nitrogen fixation requires of MtNAS2 function, as indicated by the loss of nitrogenase activity in the insertional mutant nas2-1, a phenotype reverted by reintroduction of a wild-type copy of MtNAS2. This would be the result of the altered iron distribution in nas2-1 nodules, as indicated by X-ray fluorescence studies. Moreover, iron speciation is also affected in these nodules. These data suggest a role of nicotianamine in iron delivery for symbiotic nitrogen fixation.\n\nSignificance StatementNicotianamine synthesis mediated by MtNAS2 is important for iron allocation for symbiotic nitrogen fixation by rhizobia in Medicago truncatula root nodules.

plant biology↗

bioRxiv2019

Medicago truncatula Ferroportin2 mediates iron import into nodule symbiosomes

Iron is an essential cofactor for symbiotic nitrogen fixation. It is required by many of the enzymes facilitating the conversion of N2 into NH4+ by endosymbiotic bacteria living within root nodule cells, including signal transduction proteins, O2 homeostasis systems, and nitrogenase itself. Consequently, host plants have developed a transport network to deliver essential iron to nitrogen-fixing nodule cells. Model legume Medicago truncatula Ferroportin2 (MtFPN2) is a nodule-specific gene that encodes an iron-efflux protein. MtFPN2 is located in intracellular membranes in the nodule vasculature, and in the symbiosome membranes that contain the nitrogen-fixing bacteria in the differentiation and early-fixation zones of the nodules. Loss-of-function of MtFPN2 leads to altered iron distribution and speciation in nodules, which causes a reduction in nitrogenase activity and in biomass production. Using promoters with different tissular activity to drive MtFPN2 expression in MtFPN2 mutants, we determined that MtFPN2-facilitated iron delivery across symbiosomes is essential for symbiotic nitrogen fixation, while its presence in the vasculature does not seem to play a major role in in the conditions tested.

plant biology↗