The many facets of protein ubiquitination and degradation in plant root iron-deficiency responses

Abstract

Organisms need to deal with the absolute requirement for metals, and their possible toxicity. This is achieved through an intricate network of signaling pathways integrated to ultimately fine tune iron uptake and metabolism. The mechanisms by which plants cope with iron limitation and the associated genomic responses are well characterized. On top of this transcriptional cascade is layered another level of regulation involving the post-translational modification and degradation. The ubiquitination and/or degradation of several transcription factors in the iron deficiency signaling pathways and metal transporters recently came to light. In this review we discuss about the mechanisms and on the possible roles of protein modification and turn over in the regulation of root iron deficiency responses. We also highlight the tight coupling between metal sensing by E3 ubiquitin ligases or bifunctional transporters and protein degradation.

Annotation and Molecular Characterisation of the TaIRO3 and TaHRZ Iron Homeostasis Genes in Bread Wheat (Triticum aestivum L.)

“…Given that RxLxL is an atypical EAR motif sequence, we have labelled this sequence as “EAR-like” in the TaIRO3 proteins, and further research is required to confirm whether this motif is functional in bread wheat. In contrast to the TaIRO3 proteins, the TaHRZ proteins belong to an E3-ligase family that contain conserved, putative metal-binding domains (hemerythrin, CHY-type, CTCHY-type, RING-type, and RCHY1 Zn-ribbon) that together act to post-transcriptionally regulate genes [ 10 , 55 ]. All HRZ proteins contained a conserved Zn-finger region (containing CHY-type, CTCHY-type, and RING-type motifs) at the C-terminus that is responsible for polyubiquitination and the subsequent degradation of proteins ( Figure 4 b).…”

IRONMAN Tunes Responses to Iron Deficiency in Concert with Environmental pH

“…In Arabidopsis, all Fe deficiency responses are regulated by a complex cascade of regulatory processes that orchestrate a subtle balance of promotive and repressive trans -acting factors in concert with post-translational control of central regulatory nodes (Rodrígues-Celma et al, 2019; Schwarz and Bauer, 2020; Spielmann and Vert, 2020; Gao and Dubos, 2020). Overexpression of IMA1-IMA3 was shown to induce large parts of the Fe deficiency response in Arabidopsis (Grillet et al, 2018; Hirayama et al, 2018; this study), but the exact position of IMA peptides in the regulatory network governing cellular Fe homeostasis has not yet been defined.…”

The iron will of the research community: advances in iron nutrition and interactions in lockdown times

“…Post-translational regulation also plays a role in maintaining iron homeostasis. In particular, protein ubiquitination mediates the degradation of the core bHLH transcription factors and controls the recycling and degradation of the main iron transporter IRT1 ( Dubeaux et al , 2018 ; Spielmann and Vert, 2021 ). Mechanisms for how the iron status of the cell is sensed are also emerging.…”

“…Mechanisms for how the iron status of the cell is sensed are also emerging. One of them involves the plant-specific BTS/L ubiquitin ligases that can bind iron ( Rodríguez-Celma et al , 2019 ; Spielmann and Vert, 2021 ). This proposed sensing mechanism is distinct from those in yeast and mammalian cells.…”