Molecular Evidence of CeO 2 Nanoparticle Modulation of ABA and Genes Containing ABA-Responsive Cis-Elements to Promote Rice Drought Resistance

Cerium dioxide nanoparticles (CeO NPs) have enzyme-like properties and scavenge excess ROS induced by stressors such as drought. However, the underlying molecular mechanisms by which CeO NPs enhance drought resistance are unknown. In this work, both foliar application and soil injection of CeO NPs were used to rice seedlings under a 30 day moderate drought (40% soil relative moisture). Foliar application of 4 mg of CeO 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 CeO 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. CeO 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 CeO 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.