Elucidation of mechanisms by which plants respond to stress is crucial for developing stress tolerant crops. Unlike plants, stress response mediated by eIF2α-kinases is well described in yeast and mammalian systems. We isolated a NaCl-tolerant mutant (JP2) with 35S enhancers upstream of AtGCN2. Under NaCl-stress, JP2 had 1.4 fold AtGCN2 transcripts than control. JP2 phenotype was however inconsistent, but prompted enquiry of AtGCN2-mediated plant stress response. A null mutant (atgcn2) was isolated and characterised to identify associated phenotypes and putative cold (4°C) induced transcripts under AtGCN2 control. The atgcn2 mutant had a T-DNA insertion on the 27th exon, disrupting AtGCN2 C-terminal domain. The atgcn2 mutant lacked a strong growth phenotype under optimal growth conditions, temperature acclimation and NaCl stress. Unlike WT plants, amino acid starvation, prolonged NaCl stress and temperature acclimation failed to induce phosphorylation of eIF2α in atgcn2 mutant. RNAseq revealed 37 cold-induced transcripts that were upregulated in WT and not in atgcn2 mutant. SQ-RT PCR confirmed cold-induced At4g06536, At5g15970 and At2g33790 genes were under AtGCN2 control. We therefore conclude that prolonged NaCl exposure activates AtGCN2 kinase, C-terminal domain is crucial for AtGCN2activation in planta and AtGCN2 mediates transcription of some cold response genes.

Keywords: Arabidopsis, GCN2, eIF2-α phosphorylation, C-terminal Domain, Stress response, Kinase