Mitochondrial RNA helicase SUV3 modulates photosynthetic efficiency and ROS homeostasis to confer salinity tolerance in marker-free rice (Oryza sativa L. cv. IR64)

In the era of frequently changing global climatic conditions, abiotic stresses represent the primary constraints to global crop productivity which pose serious challenges to food security. Among the molecular factors implicated in stress adaptation, helicases involved in DNA and RNA metabolism have recently gained attention as potential targets for enhancing stress tolerance in various crop plants. SUV3 (Suppressor of Var3), a mitochondrial RNA helicase (mtSUV3), plays a critical role in mitochondrial RNA processing and maintenance. However, its involvement in abiotic stress responses remains largely unexplored. In this study, we generated marker-free transgenic rice ( Oryza sativa L. cv. IR64) overexpressing mtSUV3 (mtSUV3-OE) and evaluated its functional role in salinity tolerance. Three independent marker-free transgenic rice lines were established and subjected to high salinity stress (200 mM NaCl). Compared to wild-type plants, mtSUV3-OE lines exhibited enhanced tolerance to salt stress. Stable integration and expression of transgene were confirmed by PCR, Southern blot and RT-PCR analyses. Under salt stress conditions, transgenic lines accumulated significantly higher levels of phytohormones (IAA, GA and zeatin) and endogenous sugars (glucose and fructose). Moreover, mtSUV3-OE plants displayed improved photosynthetic performance, as evidenced by increased chlorophyll content, intercellular CO₂ concentration, stomatal conductance and net photosynthetic rate. Enhanced activities of antioxidant enzymes in transgenic lines correlated with reduced oxidative stress markers, including malondialdehyde and H₂O₂ content. Collectively, these findings uncover a previously uncharacterized role for mtSUV3 in mediating salinity tolerance in rice. Marker-free overexpression of mtSUV3 has the potential to enhance rice salinity tolerance. It also addresses biosafety issues and lays the groundwork for future field testing. • Marker-free mtSUV3 overexpressing rice lines exhibit significantly enhanced tolerance to 200 mM salinity stress. • mtSUV3 overexpression improves photosynthetic efficiency and gas-exchange parameters under salt stress conditions. • Transgenic lines show enhanced antioxidant enzyme activity and reduced oxidative damage (MDA, H₂O₂) compared to wild type. • Elevated phytohormones and soluble sugars contribute to improved metabolic and physiological adaptation to salinity stress.