Transcriptomics Reveals the Pathway for Increasing <i>Brassica chinensis</i> L. Yield under Foliar Application of Titanium Oxide Nanoparticles

In this study, <i>Brassica chinensis</i> L seedlings after 6 weeks of soil cultivation were treated with foliar application of TiO₂ NPs (20 mg/L) for different times. Transcriptomics analysis was employed to investigate the impact of TiO₂ NPs on the physiology, growth, and yield of <i>B. chinensis</i> L. Results showed that TiO₂ NPs' exposure significantly increased the biomass, total phosphorus, and catalase enzyme activity by 23.60, 23.72, and 44.01%, respectively, compared to the untreated ones (not bulk or ion).TiO₂ NPs increased the leaf chlorophyll content by 4.9% and photosynthetic rate by 16.62%, which was attributed to the upregulated expression of seven genes (<i>PetH</i>, <i>PetF</i>, <i>PsaF</i>, <i>PsbA</i>, <i>PsbB</i>, <i>PsbD</i>, and <i>Lhcb</i>) associated with electron transport in photosystem I and light-harvesting in leaves. The water balance of <i>B. chinensis</i> was improved correlating with the altered expressions of 19 aquaporin genes (e.g., <i>PIP2;1</i> and <i>NIP6;1</i>). The expressions of 58 genes related to plant hormone signaling and growth were dysregulated, with notable downregulations in GA20, SnRK2, and PP2C and upregulations of DELLAs, SAM, and ETR. Moreover, the 11 tricarboxylic acid cycle genes and 13 glycolysis genes appear to stimulate pathways involved in promoting the growth and physiology of <i>B. chinensis</i>. This research contributes valuable insights into new strategies for increasing the yield of <i>B. chinensis</i>.