Involvement of the eIF2α Kinase GCN2 in UV-B Responses

Abstract

GCN2 (general control nonrepressed 2) is a serine/threonine-protein kinase that regulates translation in response to stressors such as amino acid and purin deprivation, cold shock, wounding, cadmium, and UV-C exposure. Activated GCN2 phosphorylates the α-subunit of the eukaryotic initiation factor 2 (eIF2) leading to a drastic inhibition of protein synthesis and shifting translation to specific mRNAs. To investigate the role of GCN2 in responses to UV-B radiation its activity was analyzed through eIF2α phosphorylation assays in mutants of the specific UV-B and stress signaling pathways of Arabidopsis thaliana. EIF2α phosphorylation was detectable 30 min after UV-B exposure, independent of the UV-B photoreceptor UV RESISTANCE LOCUS8 and its downstream signaling components. GCN2 dependent phosphorylation of eIF2α was also detectable in mutants of the stress related MAP kinases, MPK3 and MPK6 and their negative regulator map kinase phosphatase1 (MKP1). Transcription of downstream components of the UV-B signaling pathway, the Chalcone synthase (CHS) was constitutively higher in gcn2-1 compared to wildtype and further increased upon UV-B while GLUTATHIONE PEROXIDASE7 (GPX7) behaved similarly to wildtype. The UVR8 independent FAD-LINKED OXIDOREDUCTASE (FADox) had a lower basal expression in gcn2-1 which was increased upon UV-B. Since high fluence rates of UV-B induce DNA damage the expression of the RAS ASSOCIATED WITH DIABETES PROTEIN51 (RAD51) was quantified before and after UV-B. While the basal expression was similar to wildtype it was significantly less induced upon UV-B in the gcn2-1 mutant. This expression pattern correlates with the finding that gcn2 mutants develop less cyclobutane pyrimidine dimers after UV-B exposure. Quantification of translation with the puromycination assay revealed that gcn2 mutants have an increased rate of translation which was also higher upon UV-B. Growth of gcn2 mutants to chronic UV-B exposure supports GCN2’s role as a negative regulator of UV-B responses. The elevated resistance of gcn2 mutants towards repeated UV-B exposure points to a critical role of GCN2 in the regulation of translation upon UV-B.

Multi-Omics Analysis of Low-Temperature Fruiting Highlights the Promising Cultivation Application of the Nutrients Accumulation in Hypsizygus marmoreus

“…that regulates translation in response to stressors such as amino acid and purine deprivation, cold shock, wounding, cadmium exposure, and UV-C exposure [39]. In yeast and animals, phosphorylation of the α-subunit of eIF2 is the most thoroughly characterized event regulating global translation under stress.…”

“…A close link between the upregulation of low-temperature-associated proteins and vernalization fulfillment in wheat [ 38 ] suggests a role of cold stress-responsive genes in the vernalization-like process in H. marmoreus . GCN2 is a serine/threonine-protein kinase that regulates translation in response to stressors such as amino acid and purine deprivation, cold shock, wounding, cadmium exposure, and UV-C exposure [ 39 ]. In yeast and animals, phosphorylation of the α-subunit of eIF2 is the most thoroughly characterized event regulating global translation under stress.…”

“…GCN2 and eIF2 were upregulated under low-temperature fruiting ( Figure 5 B), indicating that low temperature stimulated the GCN2-mediated eIF2 pathway to promote global protein translation ( Figure 7 ). Activated GCN2 phosphorylates the α-subunit of eIF2, drastically inhibiting protein synthesis in most species [ 39 ]. However, GCN2-mediated protein translation in H. marmoreus promotes the activation of protein synthesis, and this constitutes a significant exception; it also occurs in wheat under cold shock [ 40 ].…”

Translational gene regulation in plants: A green new deal

“…However, other evidence indicates a broader role for GCN2 in plant translational control beyond amino acid sensing. First, plant GCN2 is activated by several abiotic stresses, pathogens, and defense‐related signaling molecules (Lageix et al, 2008; X. Liu et al, 2019; Llabata et al, 2019; Lokdarshi, Guan, et al, 2020; Sormani et al, 2011; L. Wang et al, 2017). Upon infection with Pseudomonas syringae , the GCN2‐eIF2α module is involved in the regulation of genes encoding ABA receptors, ABA biosynthetic enzymes, and ABA‐related transcription factors (X. Liu et al, 2019).…”

Light-Dependent Activation of the GCN2 Kinase Under Cold and Salt Stress Is Mediated by the Photosynthetic Status of the Chloroplast

“…GCN2 activity has been implicated in the down-regulation of mRNA translation under a variety of stress conditions (Lageix et al, 2008;Zhang et al, 2008;Liu et al, 2015a;Wang et al, 2017;Llabata et al, 2019). To test the role of GCN2 in global mRNA translation under cold and salt stress, gcn2 mutant and wildtype seedlings were challenged with the respective stresses under light.…”