Overexpression of AtBBX29 Improves Drought Tolerance by Maintaining Photosynthesis and Enhancing the Antioxidant and Osmolyte Capacity of Sugarcane Plants

B-box proteins have emerged as prominent mechanisms for controlling growth and developmental processes and in some instances responses to biotic and abiotic stresses in plants. These proteins mediate transcriptional regulations and protein–protein interactions in cellular signalling processes. B-box proteins thereby play an important role in coordinating physiological and biochemical pathway flux and are therefore ideal targets for controlling stress responses in plants. In this study, the overexpression of an Arabidopsis thaliana B-box gene (BBX29) in sugarcane (Saccharum spp. hybrid) has led to enhanced drought tolerance and delayed senescence under water-deficit conditions when compared to the wild-type plants. Transgenic plants maintained a higher relative water content and better protected its photosynthetic machinery. These plants accumulated more proline and displayed enhanced enzymatic antioxidant activity under drought conditions. Overexpression of AtBBX29 further alleviated the build-up of reactive oxygen species and curtailed oxidative damage, resulting in transgenic plants with improved health and higher survival rates during dehydration. Our results suggested that the AtBBX29 gene influenced an array of physiological and biochemical mechanisms in sugarcane to the advantage of the crop and might be a target to genetically engineer drought tolerance into sugarcane. This is the first report to elucidate B-box protein functionality in a polyploid crop such as sugarcane.