Overexpression of METAL TOLERANCE PROTEIN8 reveals new aspects of metal transport in Arabidopsis thaliana seeds

Abstract

METAL TOLERANCE PROTEIN8 (MTP8) of Arabidopsis thaliana is a member of the CATION DIFFUSION FACILITATOR (CDF) family of proteins that transports primarily manganese (Mn), but also iron (Fe). MTP8 mediates Mn allocation to specific cell types in the developing embryo, and Fe re-allocation as well as Mn tolerance during imbibition. We analysed if an overexpression of MTP8 driven by the CaMV 35S promoter has an effect on Mn tolerance during imbibition and on Mn and Fe storage in seeds, which would render it a biofortification target.• Fe, Mn and Zn concentrations in MTP8-overexpressing lines in wild type and vit1-1 backgrounds were analysed by ICP-MS. Distribution of metals in intact seeds was determined by synchrotron µXRF tomography.• MTP8 overexpression led to a strongly increased Mn tolerance of seeds during imbibition, supporting its effectiveness in loading excess Mn into the vacuole. In mature seeds, MTP8 overexpression did not cause a consistent increase in Mn and Fe accumulation, and it did not change the allocation pattern of these metals. Zn concentrations were consistently increased in bulk samples.• The results demonstrate that Mn and Fe allocation is not determined primarily by the MTP8 expression pattern, suggesting either a cell type-specific provision of metals for vacuolar sequestration by upstream transport processes, or the determination of MTP8 activity by post-translational regulation.

The vacuolar transporterLaMTP8.1 detoxifies manganese in leaves ofLupinus albus

“…1 expression strength did not reflect the preferential accumulation of Mn in old leaves of plants grown under control conditions. This suggests the operation of further mechanisms of Mn allocation that may act on, upstream of, or in parallel to LaMTP8 , similar to what has been observed in Mn distribution in Arabidopsis embryos (Höller et al, 2022).…”

“…Arabidopsis MTP8 is regulated by phosphorylation of serine residues at its N‐terminal domain by calcium‐dependent protein kinases (CPK 4/5/6/11; Zhang et al, 2021) and calcineurin B‐like proteins (CBL2/3) and their interacting kinases (CIPK3/9/26; Ju et al, 2022). In Arabidopsis, MTP8 has a further role in mediating Mn storage in vacuoles of subepidermal cells of developing embryos (Eroglu et al, 2017; Höller et al, 2022). Besides Mn, MTP8 transports Fe, which appears to be relevant for the storage of remobilized Fe during imbibition and germination (Eroglu et al, 2017).…”

Size- and Ligand-Dependent Transport of Nanoparticles in Matricaria chamomilla as Demonstrated by Mass Spectroscopy and X-ray Fluorescence Imaging

“…This technology allows for the study of naturally occurring elements important to plant metabolism or disease course ( i.e ., Fe, Cu, Zn, Mn, etc .) with different spatial resolution (μm or nm), − as well as exogenous environmental elements present as contaminants accumulated by plant species ( i.e ., La, Ce, As, etc . ). , For example, XFI mapping and tomography were used to demonstrate a correlation between Zn and Fe homeostasis, as Zn can be found in the chloroplasts and mitochondria of leaf cells in Fe-deficient plants .…”

The trans-Golgi-localized protein BICAT3 regulates manganese allocation and matrix polysaccharide biosynthesis

“…The pathway of xylem loading is dubious in dicots ( Alejandro et al, 2020 ). Intracellularly, Mn 2+ may be sequestrated in vacuoles by CATION DIFFUSION FACILITATOR/METAL TOLERANCE PROTEIN (CDF/MTP) and CATION/H + EXCHANGER (CAX) transporters, which is an important mechanism of its detoxification and its storage in seeds ( Eroglu et al, 2016 , 2017 ; He et al, 2021 ; Höller et al, 2022 ). Transfer of Mn 2+ into the endoplasmic reticulum by the P 2A -type ATPase ER-TYPE CA 2+ -ATPASE 1 (ECA1) also confers tolerance to the metal ( Liang et al, 1997 ).…”