Phosphorylation of Arabidopsis eIF4E and eIFiso4E by SnRK1 inhibits translation

Abstract

Regulation of protein synthesis is critical for maintaining cellular homeostasis. In mammalian systems, translational regulatory networks have been elucidated in considerable detail. In plants, however, regulation occurs through different mechanisms that remain largely elusive. In this study, we present evidence that the Arabidopsis thaliana energy sensing kinase SnRK1, a homologue of mammalian AMP-activated kinase and yeast sucrose non-fermenting 1 (SNF1), inhibits translation by phosphorylating the cap binding proteins eIF4E and eIFiso4E. We establish that eIF4E and eIFiso4E contain two deeply conserved SnRK1 consensus target sites and that both interact with SnRK1 in vivo. We then demonstrate that SnRK1 phosphorylation inhibits the ability of Arabidopsis eIF4E and eIFiso4E to complement a yeast strain lacking endogenous eIF4E, and that inhibition correlates with repression of polysome formation. Finally, we show that SnRK1 over-expression in Nicotiana benthamiana plants reduces polysome formation, and that this effect can be counteracted by transient expression of eIF4E or mutant eIF4E containing non-phosphorylatable SnRK1 target residues, but not by a phosphomimic eIF4E. Together, these studies elucidate a novel and direct pathway for translational control in plant cells. In light of previous findings that SnRK1 conditions an innate antiviral defense and is inhibited by geminivirus pathogenicity factors, we speculate that phosphorylation of cap binding proteins may be a component of the resistance mechanism.Abbreviations AD, activation domain; ADK, adenosine kinase; AMPK, AMP-activated kinase; BD, binding domain; BiFC, bimolecular fluorescence complementation; CBE1, conserved binding of eIF4E1; DCL4, Dicer-like 4; DRB4, double-stranded RNA binding protein 4; eIF4E, eukaryotic initiation factor 4E; eIFiso4E, eukaryotic initiation factor iso4E; GPD, glyceraldehyde-3-phosphate dehydrogenase; GST, glutathione-Stransferase; RFP, red fluorescent protein; rRNA, ribosomal RNA; SNF1, sucrose non-fermenting 1; SNF1, sucrose non-fermenting 1; SnRK1-KDKR, SnRK1 kinase domain inactive.; SnRK1-KD, SnRK1 kinase domain; SnRK1, SNF1-related kinase 1; TOR, target of rapamycin; YFP, yellow fluorescent protein.A. N. Bruns et al.SnRK1 phosphorylates eIF4E and eIFiso4E

Attenuation of cytosolic translation by RNA oxidation is involved in singlet oxygen‐mediated transcriptomic responses

“…Another layer of cellular control of translation in stress can be achieved by the phosphorylation of eIF4E and eIFiso4E that attenuates translation by preventing its initiation (Bruns, Li, Mohannath, & Bisaro, 2019;Merchante, Stepanova, & Alonso, 2017). Thus, additional molecular mechanisms for global translation attenuation may come into play during stress alongside the novel mechanism of direct RNA oxidation explored here.…”

A Novel Interaction Network Used by Potyviruses in Virus–Host Interactions at the Protein Level

“…CBE1 is a constituent of 4E cap-binding complexes and has the potential to regulate gene expression [22]. Plant 4Es can also be phosphorylated at the lateral surface of 4E by the energy-sensing kinase SnRK1, which inhibits translation [23]. Phosphorylation of 4E increases binding of VPg [24].…”

Abscisic Acid Connects Phytohormone Signaling with RNA Metabolic Pathways and Promotes an Antiviral Response that Is Evaded by a Self-Controlled RNA Virus

“…Translation inhibition, RNA maturation and turnover, and their regulation by phosphorylation events have critical roles in the antiviral immune responses of human cells ( Narayanan and Makino, 2013 ; McCormick and Khaperskyy, 2017 ; Boudreault et al, 2019 ). In plants, phosphorylation events promote RNA decay in response to bacteria and abiotic stress ( Xu and Chua, 2012 ; Soma et al, 2017 ; Yu et al, 2019 ), inhibit or disrupt the translation of host transcripts ( Bruns et al, 2019 ; Cho et al, 2019 ), and have been suggested to alter RNA maturation by affecting the activity or subcellular distribution of splicing factors ( Laloum et al, 2018 ). Consistent with these studies, results of our phosphoproteomic meta-analysis revealed ABA-dependent responsiveness of the phosphorylation status of host components that regulate RNA stability, turnover, maturation, and translation initiation.…”