Target of Rapamycin (TOR) negatively regulates chlorophyll degradation and lipid peroxidation and controls responses under abiotic stress in Arabidopsis thaliana

The Target of Rapamycin (TOR) is a conserved multifunctional Serine/Threonine protein kinase present in all eukaryotes, which controls several important signaling pathways related to growth and development. In the present investigation, we report that TOR overexpressing Arabidopsis plants ATR-1.4.27, and ATR-3.7.32 exhibit enhanced tolerance to osmotic and salt stress treatments. The TOR overexpressing lines ATR-1.4.27, and ATR-3.7.32 treated with mannitol (100 mM), NaCl (150 mM), sorbitol (200 mM), and PEG (7% w/v), showed improved performance in root growth, fresh weight, and lateral root density. The transgenic lines also exhibited increased proline and chlorophyll contents along with the significant upregulation of stress-responsive genes compared with their corresponding treated and untreated wild-type (WT) controls. More than 90% degradation of chlorophyll-a, chlorophyll b, and total chlorophyll contents was observed in WT plants under each stress treatment, whereas the two transgenic lines had very low degradation ranging from 40% to 50%. Stress treated TOR-OE lines also showed decreased malondialdehyde (MDA) content, and high chlorophyll fluorescence of PhotosystemII (PSII; F-v/F-m ratio) compared with the treated WT control. Taken together, our results show that the constitutive overexpression of TOR enhances salt and osmotic stress tolerance in Arabidopsis thaliana.