Vacuolar iron stores gated by NRAMP3 and NRAMP4 are the primary source of iron in germinating seeds

Bastow, E. L., Garcia de la Torre, V. S., MacLean, A. E., Green, R. T., Merlot, S., Thomine, S. and Balk, J. (2018) Vacuolar iron stores gated by NRAMP3 and NRAMP4 are the primary source of iron in germinating seeds. Plant Physiology, 177(3), pp. 1267-1276. (doi:10.1104/pp.18.00478) (PMID:29784767)

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Abstract

During seed germination, iron (Fe) stored in vacuoles is exported by the redundant NRAMP3 and NRAMP4 transporter proteins. A double nramp3 nramp4 mutant is unable to mobilize Fe stores and does not develop in the absence of external Fe. We used RNA sequencing to compare gene expression in nramp3 nramp4 and wild type during germination and early seedling development. Even though sufficient Fe was supplied, the Fe-responsive transcription factors bHLH38, 39, 100, and 101 and their downstream targets FRO2 and IRT1 mediating Fe uptake were strongly upregulated in the nramp3 nramp4 mutant. Activation of the Fe deficiency response was confirmed by increased ferric chelate reductase activity in the mutant. At early stages, genes important for chloroplast redox control (FSD1 and SAPX), Fe homeostasis (FER1 and SUFB), and chlorophyll metabolism (HEMA1 and NYC1) were downregulated, indicating limited Fe availability in plastids. In contrast, expression of FRO3, encoding a ferric reductase involved in Fe import into the mitochondria, was maintained, and Fe-dependent enzymes in the mitochondria were unaffected in nramp3 nramp4. Together, these data show that a failure to mobilize Fe stores during germination triggered Fe deficiency responses and strongly affected plastids, but not mitochondria.

Item Type:Articles
Additional Information:Funding: the Biotechnology and Biological Sciences Research Council (BBSRC; BB/K008838/1 to E.L.B. and J.B.); BBSRC institute strategic program grants (BB/P012523/1 and BB/P012574/1 to R.T.G. and J.B.); the John Innes Foundation to A.E.M.; Agence Nationale de la Recherche grants ANR-16-CE20-0019-02 to S.T. and ANR-13- ADAP-0004 to S.M.; and LabEx Saclay Plant Sciences-SPS (ANR-10-LABX-0040-SPS) to S.M. and S.T.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:MacLean, Dr Andrew
Authors: Bastow, E. L., Garcia de la Torre, V. S., MacLean, A. E., Green, R. T., Merlot, S., Thomine, S., and Balk, J.
College/School:College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Journal Name:Plant Physiology
Publisher:American Society of Plant Biologists
ISSN:0032-0889
ISSN (Online):1532-2548
Published Online:21 May 2018
Copyright Holders:Copyright © 2018 American Society of Plant Biologists
First Published:First published in Plant Physiology 177(3):1267-1276
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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