Control of translation during the unfolded protein response in maize seedlings: Life without PERKs.

Pulkit Kanodia,Stephen H Howell,Ran Bi,W Allen Miller,Peng Liu,Renu Srivastava,Paramasivan Vijayapalani

doi:10.1002/pld3.241

Pulkit Kanodia, Stephen H Howell + Show 5 more

Open Access

https://doi.org/10.1002/pld3.241

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Journal: Plant Direct	Publication Date: Jul 1, 2020
Citations: 11	License type: CC BY 4.0

Affiliation: Iowa State University

Abstract

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) defines a condition called ER stress that induces the unfolded protein response (UPR). The UPR in mammalian cells attenuates protein synthesis initiation, which prevents the piling up of misfolded proteins in the ER. Mammalian cells rely on Protein Kinase RNA‐Like Endoplasmic Reticulum Kinase (PERK) phosphorylation of eIF2α to arrest protein synthesis, however, plants do not have a PERK homolog, so the question is whether plants control translation in response to ER stress. We compared changes in RNA levels in the transcriptome to the RNA levels protected by ribosomes and found a decline in translation efficiency, including many UPR genes, in response to ER stress. The decline in translation efficiency is due to the fact that many mRNAs are not loaded onto polyribosomes (polysomes) in proportion to their increase in total RNA, instead some of the transcripts accumulate in stress granules (SGs). The RNAs that populate SGs are not derived from the disassembly of polysomes because protein synthesis remains steady during stress. Thus, the surge in transcription of UPR genes in response to ER stress is accompanied by the formation of SGs, and the sequestration of mRNAs in SGs may serve to temporarily relieve the translation load during ER stress.

Highlights

A major challenge for plant scientists is to understand how plants adapt to climate change given the prediction for greater weather extremes in the future
Translation initiation in mammalian cells is attenuated by the action of Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK) (Yan et al, 2002), an endoplasmic reticulum (ER) membrane enzyme which is activated by ER stress to phosphorylate the translation initiation factor eIF2α (Harding, Novoa, et al, 2000)
It has been reasoned that attenuation prevents the further piling up of misfolded proteins in the ER when the demand exceeds the capacity for folding

Summary

| INTRODUCTION

A major challenge for plant scientists is to understand how plants adapt to climate change given the prediction for greater weather extremes in the future. Translation initiation in mammalian cells is attenuated by the action of Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK) (Yan et al, 2002), an ER membrane enzyme which is activated by ER stress to phosphorylate the translation initiation factor eIF2α (Harding, Novoa, et al, 2000). Arabidopsis eIF2α is phosphorylated following treatment with herbicides, such as glyphosate or chlorsulfuron, that block amino acid biosynthesis (Lageix et al, 2008; Zhang et al, 2008) Another means by which ER stress can attenuate general protein synthesis is through the activation of regulated IRE1-dependent decay of mRNA (RIDD) (Hollien & Weissman, 2006). We provide evidence that many of the UPR gene transcripts are not loaded onto polysomes, but they accumulate in SGs instead

| MATERIALS AND METHODS

| DISCUSSION