Zinc and iron cross-homeostasis in Arabidopsis thaliana

Stanton, Camilla (2021) Zinc and iron cross-homeostasis in Arabidopsis thaliana. Doctoral thesis, University of East Anglia.

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Abstract

Zinc (Zn) and iron (Fe) are essential micronutrients in all biological systems, being utilised by thousands of enzymes and regulatory proteins as cofactors and structural components. In plants, nutrition is closely interlinked, with Zn excess causing secondary Fe deficiency. Highly coordinated homeostatic mechanisms have evolved to maintain optimal cellular Zn and Fe concentrations, although little is known about the regulatory proteins involved in cross-talk between these homeostasis networks. The aim of this thesis is to uncover novel components involved in Zn and Fe cross-homeostasis in Arabidopsis thaliana using forward and reverse genetic approaches.

Two reporter-based mutant screens were established to identify new genes and mutant alleles involved in the Zn deficiency and excess response. Transgenic lines expressing firefly luciferase (LUC) under the control of a Zn deficiency-responsive promoter, Zrt-/Irt-Like Protein 5 (ZIP5), or a Zn excess and Fe deficiency-responsive promoter, Ferric Reduction Oxidase 3 (FRO3), were generated. Initial screening of EMS-mutagenised populations failed to identify any candidate mutants but helped to establish screening populations and optimise screening protocols for future research.

Previously, BRUTUS-LIKE 1 (BTSL1) and BTSL2 were identified as partially functionally redundant E3 ubiquitin ligases that negatively regulate Fe uptake by targeting a central regulator of Fe deficiency, FER-like Fe deficiency Induced Transcription factor (FIT), for proteasomal degradation. Enhanced Fe uptake capacity in the btsl double mutant confers tolerance to Fe deficiency, and here it is shown that BTSL1 and BTSL2 also impact Zn uptake and distribution, conferring an Fe-mediated Zn tolerance phenotype. The btsl double mutant shows constitutive expression of FIT-dependent and FIT-independent metal homeostasis genes in roots, suggesting that BTSL proteins have additional transcription factor targets upstream of FIT as well. Furthermore, the btsl mutant is insensitive to systemic Fe signalling, showing that BTSL proteins are regulated by both local and systemic Fe signals, likely mediated by the cellular ratio of Zn and Fe. Together, the work presented in this thesis proposes a new role for BTSL proteins in regulating Zn and Fe cross-homeostasis in plants.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	19 Oct 2021 09:41
Last Modified:	19 Oct 2021 09:41
URI:	https://ueaeprints.uea.ac.uk/id/eprint/81785
DOI:

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