Ectopic expression of choline oxidase (codA) gene from Arthrobacter globiformis confers drought stress tolerance in transgenic sugarcane

Drought is a serious problem that impacts sugarcane production and productivity worldwide. In this current investigation, a codon-optimized choline oxidase (codA) gene was transformed into Saccharum hybrid cultivar Co 86032 through Agrobacterium-mediated transformation. The transgenic events with the codA gene driven by the portubi882 (PD2) promoter accumulated elevated levels of glycine betaine (5 – 10µg/g) whereas untransformed control plants accumulated less than 1.5µg/g which in turn maintained the plant health by sustaining transpiration rate (4 – 5 µmol of H₂O/cm²/s) and photosynthetic efficiency (30 – 34 µmol/Co₂/s) whereas the control plants suffered from 50% reduction under water-deficit stress condition. Morpho-anatomic cross-sections of both transgenic events and control plants exhibited significant differences in the epidermal layer and sclerenchyma cells under stress conditions. The relative water content (71 – 76%) and chlorophyll fluorescence (0.60 – 0.72 Fv/Fm) were higher in transgenic events compared to control plants respectively recorded 59% and 0.50 respectively. In addition, significantly elevated activity of antioxidant enzymes viz., superoxide dismutase (95 – 102 U/g), catalase (65 – 73 umol/min/g), ascorbate peroxidase (1700 – 1900 umol/min/mg) and glutathione reductase (17 – 20 umol/min/mg) were observed in transgenic events along with reduced levels of hydrogen peroxide (14 – 16 µmol/g) and malondialdehyde (14 – 17 nmol/g) content. Transgenic events recorded significantly higher arial biomass content compared to untransformed plant after the drought stress. Overall, the increased expression levels of codA gene in sugarcane events resulted in an enhanced ability to withstand water-deficit conditions.