AUTHOR=Llabata Paula , Richter Julia , Faus Isabel , Słomiňska-Durdasiak Karolina , Zeh Lukas Hubert , Gadea Jose , Hauser Marie-Theres 

TITLE=Involvement of the eIF2α Kinase GCN2 in UV-B Responses

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01492

DOI=10.3389/fpls.2019.01492

ISSN=1664-462X

ABSTRACT=<p><italic>GCN2</italic> (<italic>general control nonrepressed 2</italic>) 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 <italic>GCN2</italic> 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 <italic>GCN2</italic> 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 <italic>Arabidopsis thaliana</italic>. EIF2α phosphorylation was detectable 30 min after UV-B exposure, independent of the UV-B photoreceptor <italic>UV RESISTANCE LOCUS8</italic> and its downstream signaling components. GCN2 dependent phosphorylation of eIF2α was also detectable in mutants of the stress related MAP kinases, <italic>MPK3</italic> and <italic>MPK6</italic> and their negative regulator <italic>map kinase phosphatase1</italic> (<italic>MKP</italic>1). Transcription of downstream components of the UV-B signaling pathway, the <italic>Chalcone synthase</italic> (<italic>CHS</italic>) was constitutively higher in <italic>gcn2-1</italic> compared to wildtype and further increased upon UV-B while <italic>GLUTATHIONE PEROXIDASE7</italic> (<italic>GPX7</italic>) behaved similarly to wildtype. The UVR8 independent <italic>FAD-LINKED OXIDOREDUCTASE</italic> (<italic>FADox</italic>) had a lower basal expression in <italic>gcn2-1</italic> which was increased upon UV-B. Since high fluence rates of UV-B induce DNA damage the expression of the <italic>RAS ASSOCIATED WITH DIABETES PROTEIN51</italic> (<italic>RAD51</italic>) 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 <italic>gcn2-1</italic> mutant. This expression pattern correlates with the finding that <italic>gcn2</italic> mutants develop less cyclobutane pyrimidine dimers after UV-B exposure. Quantification of translation with the puromycination assay revealed that <italic>gcn2</italic> mutants have an increased rate of translation which was also higher upon UV-B. Growth of <italic>gcn2</italic> mutants to chronic UV-B exposure supports <italic>GCN2</italic>’s role as a negative regulator of UV-B responses. The elevated resistance of <italic>gcn2</italic> mutants towards repeated UV-B exposure points to a critical role of <italic>GCN2</italic> in the regulation of translation upon UV-B.</p>