Small-Molecules Selectively Modulate Iron-Deficiency Signaling Networks in Arabidopsis

Abstract

Plant growth requires optimal levels of iron (Fe). Fe is used for energy production, numerous enzymatic processes, and is indispensable for cellular metabolism. Recent studies have established the mechanism involved in Fe uptake and transport. However, our knowledge of Fe sensing and signaling is limited. Dissecting Fe signaling may be useful for crop improvement by Fe fortification. Here, we report two small-molecules, R3 and R6 [where R denotes repressor of IRON-REGULATED TRANSPORTER 1 (IRT1)], identified through a chemical screening, whose use blocked activation of the Fe-deficiency response in Arabidopsis thaliana. Physiological analysis of plants treated with R3 and R6 showed that these small molecules drastically attenuated the plant response to Fe starvation. Small-molecule treatment caused severe chlorosis and strongly reduced chlorophyll levels in plants. Fe content in shoots was decreased considerably by small-molecule treatments especially in Fe deficiency. Small-molecule treatments attenuated the Fe-deficiency-induced expression of the Fe uptake gene IRT1. Analysis of FER-LIKE IRON-DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT) and subgroup Ib basic helix-loop-helix (bHLH) gene (bHLH38/39/100/101) expression showed that R3 affects the FIT-network, whereas R6 affects both the FIT and Ib bHLH networks. An assessment of the effects of the structural analogs of R3 and R6 on the induction of Fe-dependent chlorosis revealed the functional motif of the investigated chemicals. Our findings suggest that small-molecules selectively modulate the distinct signaling routes that operate in response to Fe-deficiency. R3 and R6 likely interrupt the activity of key upstream signaling regulators whose activities are required for the activation of the Fe-starvation transcriptional cascade in Arabidopsis roots.

The PUB4 E3 Ubiquitin Ligase Is Responsible for the Variegated Phenotype Observed upon Alteration of Chloroplast Protein Homeostasis in Arabidopsis Cotyledons

“…Transmission electron microscopy analyses of ftsh2 and ftsh5 leaves revealed, indeed, correctly-shaped chloroplasts in the green sectors, while the white sectors showed miss-shaped plastids with highly vacuolated organelle structures [ 6 , 9 ]. Furthermore, second-site suppressor screens aimed to identify mutations able to suppress the ftsh leaf variegated phenotype, so-called Suppressors of Variegation (SVR), allowed the identification of several nuclear genes encoding plastid-located proteins mostly involved in rRNA maturation, translation, protein folding and protein degradation [ 3 , 10 , 11 , 12 , 13 , 14 ]. Overall, these findings indicated that the differentiation of functional chloroplasts requires an optimal balance between the rate of plastid protein synthesis and the activity of the plastid protein quality control machinery [ 15 ].…”

QTL and candidate gene analyses of rootstock-mediated tomato fruit yield and quality traits under low iron stress

“…Genes involved in Fe acquisition and distribution have been previously identified by the reverse genetic strategy through expression studies in mutants and transgenic genotypes in Arabidopsis and tomato (Kobayashi and Nishizawa 2012;Connort et al 2017). For Fe uptake, coumarins, facilitated by the PDR9/ABCG37 transporter (Fourcroy et al 2014;Tsai and Schmidt 2017) and protons, mediated by a plasmalemma P-Type ATPase (AHA2) (Santi and Schmidt 2009) are pumped to the rhizosphere to increase Fe 3+ solubility (Kailasam et al 2019). The secretion of coumarins (derived from precursors of the phenylpropanoid pathway) is dependent on specific β-glucosidases (Clemens and Weber 2015).…”

“…In plastids, several thousand Fe atoms are stored per ferritin molecule (Briat et al 2010). Regulation of iron homeostasis is essential and it occurs through the action of positive and negative regulators (Kailasam et al 2019). Iron uptake and transport is coordinated by transcription factors including FER in tomato (FIT in Arabidopsis) and many others from the basic Helix-Loop-Helix (bHLH), MYB and WKY families.…”

“…Iron uptake and transport is coordinated by transcription factors including FER in tomato (FIT in Arabidopsis) and many others from the basic Helix-Loop-Helix (bHLH), MYB and WKY families. Phytohormones ethylene, auxin (in the shoot-to-root regulation), as well as molecules such as nitric oxide and sucrose (promoting auxin signaling) positively regulate Fe-deficiency transcription, while others act negatively on the network (Kailasam et al 2019;Liu et al 2016;Li and Lan 2017;Lin et al 2016;Lucena et al 2006).…”

Tissue-specific signatures of metabolites and proteins in asparagus roots and exudates

“…It is known that nucleosides and nucleobases can pass plant membranes via several transport proteins 27 , and plant roots can take up and metabolize nucleosides for degradation, or utilize them in more efficient salvaging processes 28 . However, the extracellular nucleotide ATP has been identified as a plant-surface signaling molecule, with functions in stress and wounding responses of roots 29 – 31 .…”