Overexpression of the Sweet Potato ORANGE (IbOr) Gene Enhances Water Deficit Tolerance in Arabidopsis thaliana

Abstract

: Water-deficit stress is a major environmental constraint that limits plant growth and productivity, highlighting the importance of identifying genetic factors that enhance stress tolerance. To evaluate the response of Arabidopsis thaliana plants overexpressing the Ipomoea batatas ORANGE gene ( IbOr ) under water-deficit and osmotic stress, empty vector (EV) controls and IbOr-OX lines were examined using two complementary stress systems: hydroponic 10% (w/v) polyethylene glycol 6000 (PEG-6000)-induced water-deficit stress and in vitro 200 mM mannitol-induced osmotic stress. Under PEG-6000-induced water-deficit stress, IbOr-OX lines exhibited less pronounced morphological damage, including leaf wilting, chlorosis, and desiccation, than EV plants. PEG-6000-induced water-deficit stress decreased fresh weight and relative water content (RWC) in all lines, although these reductions were less pronounced in IbOr-OX44. Furthermore, under PEG-6000-induced water-deficit stress, the IbOr-OX lines maintained higher total chlorophyll and carotenoid levels than EV plants. Under PEG-6000-induced water-deficit stress, H 2 O 2 and malondialdehyde (MDA) levels were significantly lower in the IbOr-OX lines than in EV plants. This pattern was accompanied by line-dependent changes in antioxidant enzyme activities, with particularly strong induction of catalase (CAT) in IbOr-OX44 and guaiacol peroxidase (POD) in IbOr-OX34. To further characterize molecular and metabolic responses associated with IbOr overexpression, soluble sugar accumulation and the transcriptional profiles of nine carotenoid-and ABA-related genes ( GGPS1 , ABI2 , AAO3 , NCED3 , ZEP , ABA2 , PSY , ABF3 , and RD20 ) were examined under mannitol-induced osmotic stress. Mannitol-induced osmotic stress markedly increased soluble sugar accumulation in all lines, with the highest level observed in IbOr-OX34. Mannitol-induced osmotic stress also produced line-dependent changes in the expression of carotenoid biosynthesis-and ABA signaling-related genes, including GGPS1 , PSY , ABI2 , and ABF3 . Together, these findings suggest that IbOr overexpression is associated with enhanced soluble sugar accumulation, altered ROS homeostasis, and changes in ABA-related biosynthetic and signaling responses that may contribute to stress tolerance in A. thaliana .