Transcriptome Reveals the Rice Response to Elevated Free Air CO Concentration and TiO Nanoparticles.

Increasing CO levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice ( L. cv. IIyou) response to TiO nanoparticles (nano-TiO, 0 and 200 mg kg) using a free-air CO enrichment system with different CO levels (ambient ∼370 μmol mol and elevated ∼570 μmol mol). The results showed that elevated CO or nano-TiO alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO, elevated CO significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO and nano-TiO might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.