Overexpression of Tobacco GCN2 Stimulates Multiple Physiological Changes Associated With Stress Tolerance

Abstract

General control non-derepressible-2 (GCN2) is a ubiquitous protein kinase that phosphorylates the α subunit of the eukaryotic initiation factor, eIF2, preventing the initiation of a new cycle of protein synthesis, subsequently reducing the global protein biosynthesis. GCN2 can also regulate the response of plants to biotic and abiotic stresses. In this study, two GCN2 homologs, NtGCN2-1 and NtGCN2-2, were cloned from Nicotiana tabacum, and were predicted to have been derived from their progenitors in N. tomentosiformis and N. sylvestris, respectively. The phosphorylation of NteIF2α could be activated by promoting the expression of NtGCN2 with plant hormones, including salicylic acid (SA), azelaic acid (AZA), methyl jasmonate (MeJA), and by imposition of different stresses (Bemisia tabaci infection, drought, and cold), indicating that NtGCN2 is involved in the response of plants to multiple biotic and abiotic stresses. We also observed that the overexpression of NtGCN2-1 significantly influenced different physiological processes. It promoted seed germination and root elongation. The content of total soluble sugars and reducing sugars were decreased, whereas those of chlorophyll a and b were increased in the GCN2 overexpressing plants. In addition, the overexpressing plants had lower content of reactive oxygen species and exhibited higher antioxidant activities. These physiological alterations could be attributed to the changes in the endogenous phytohormones, decrease in the SA and abscisic acid content, and accumulation of MeJA and AZA. It indicated that the overexpression of NtGCN2 in tobacco, stimulated the plant defense responses via phosphorylation of NteIF2α and regulation of plant hormones, and changes in the antioxidant ability and plant nutrient status.

eIF2α Phosphorylation by GCN2 Is Induced in the Presence of Chitin and Plays an Important Role in Plant Defense against B. cinerea Infection

“…Altogether, the results indicate that GCN2 is involved in plant immunity against the necrotrophic fungus B. cinerea . These results are in accordance with the reduced induction of ET- and JA-related mRNAs in the gcn2 mutant analyzed by (Faus et al, 2015) and with the high production of MeJA and the lower accumulation of SA in the NtGCN2 overexpressing plants [ 14 ].…”

“…Until now, different studies demonstrated that GCN2 is involved in eIF2α phosphorylation in response to other pathogens and to different phytohormones associated to plant immunity [ 7 , 14 , 15 ]. In this study, we report that GCN2 is also involved in plant defense against B. cinerea infection.…”

“…Plant GCN2 has also been involved in other specific developmental programs, abiotic stress responses, and defense [ 7 , 14 , 15 ]. In this latter sense, it has been described that GCN2-mediated eIF2α phosphorylation is induced by wounding and by hormones involved in plant defense such as salicylic acid (SA), jasmonic acid (JA), methyl jasmonate (MeJA), and the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC) [ 7 , 14 ]. In addition, GCN2-mediated eIF2α-P is induced by the presence of the whitefly Bemisia tabaci in tobacco plants [ 14 ] and in response to bacterial infection by P. syringae pv.…”

Perception of double‐stranded RNA in plant antiviral immunity

“…2b,c). Nevertheless, eIF2 alpha phosphorylation has been shown to take place in response to Pseudomonas syringae infection and upon infection by Bemisia tabaci (Li et al, 2018a;Pajerowska-Mukhtar et al, 2012) as well as in response to treatment with plant hormones involved in pathogen defence and the priming agent beta-aminobutyric acid (Lageix et al, 2008, Li et al, 2018a, Liu et al, 2015, Luna et al, 2014, Wang et al, 2017. Thus, additional studies are needed to clarify the specific function of eIF2 alpha phosphorylation upon biotic stress and to further define the conditions under which it is induced.…”

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

“…Even the stimulation of GCN2 by inhibitors of amino acid biosynthesis requires light and does not occur in darkness, suggesting that ROS are an essential requirement for GCN2 activation (Lokdarshi et al, 2020). A second conundrum surrounding plant GCN2 is that gcn2 mutants have rather mild phenotypes under favorable lab conditions (Liu et al, 2015b) and a near-normal transcriptome (Faus et al, 2015;Lokdarshi et al, 2020). Moreover, among the various treatments that activate eIF2α phosphorylation, the herbicide chlorosulfuron is the only one that also results in a GCN2-dependent global translational repression (Lageix et al, 2008;Lokdarshi et al, 2020).…”