Zinc oxide nanoparticles (ZnONPs) influenced seed development, grain quality, and remobilization by affecting the transcription of microRNA 171 (miR171), miR156, NAM, and SUT genes in wheat (Triticum aestivum): a biological advantage and risk assessment study

Limited studies have been conducted on the role of microRNAs (miRs) and transcription factors in regulating plant cell responses to nanoparticles. This study attempted to address whether the foliar application of zinc oxide nanoparticles (ZnONPs; 0, 10, 25, and 50 mgL^-1) can affect miRs, gene expression, and wheat grain quality. The seedlings were sprayed with ZnONPs (0, 10, 25, and 50 mgL^-1) or bulk counterpart (BZnO) five times at 72 h intervals. The application of ZnONPs at 10 mgL^-1 increased the number of spikelets and seed weight, while the nano-supplement at 50 mgL^-1 was accompanied by severe restriction on developing spikes and grains. ZnONPs, in a dose-dependent manner, transcriptionally influenced miR156 and miR171. The expression of miR171 showed a similar trend to that of miR156. The ZnONPs at optimum concentration upregulated the NAM transcription factor and sucrose transporter (SUT) at transcriptional levels. However, the transcription of both NAM and SUT genes displayed a downward trend in response to the toxic dose of ZnONPs (50 mgL^-1). Utilization of ZnONPs increased proline and total soluble phenolic content. Monitoring the accumulation of carbohydrates, including fructan, glucose, fructose, and sucrose, revealed that ZnONPs at 10 mgL^-1 modified the source/sink communication and nutrient remobilization. The molecular and physiological data revealed that the expression of miR156 and miR171 is tightly linked to seed grain development, remobilization of carbohydrates, and genes involved in nutrient transportation. This study establishes a novel strategy for obtaining higher yields in crops. This biological risk assessment investigation also displays the potential hazard of applying ZnONPs at the flowering developmental phase.