Molecular Evidence of CeO2 Nanoparticle Modulation of ABA and Genes Containing ABA-Responsive Cis-Elements to Promote Rice Drought Resistance

Cerium dioxide nanoparticles (CeO₂ NPs) have enzyme-like properties and scavenge excess ROS induced by stressors such as drought. However, the underlying molecular mechanisms by which CeO₂ NPs enhance drought resistance are unknown. In this work, both foliar application and soil injection of CeO₂ NPs were used to rice seedlings under a 30 day moderate drought (40% soil relative moisture). Foliar application of 4 mg of CeO₂ NPs per pot reduced excess reactive oxygen species and abscisic acid (ABA) in rice leaves, thereby maintaining chloroplast structural integrity and photosynthetic output, ultimately increasing drought-stressed rice biomass by 31.3%. Genes associated with photosynthesis and ribosome activity provided the foundation by which CeO₂ NPs enhanced rice drought resistance. Importantly, these genes were tightly regulated by ABA due to the large number of abscisic acid responsive elements in their promoter regions. CeO₂ NPs also upregulated the expression of soluble sugar and fatty acid synthesis associated genes in drought-stressed rice, thereby contributing to osmotic balance and membrane lipid stability. These results highlight the potential of CeO₂ NPs to enhance rice photosynthesis and drought-resistant biomolecule accumulation by regulating ABA-dependent responses. This work provides further evidence demonstrating nanomaterials have great potential to sustainably promote stress resistance and climate resilient crops.