Titanium dioxide nanoparticles affect the growth and microRNA expression of tobacco (Nicotiana tabacum)

Titanium dioxide (TiO2) is one of the most widely used pigments in the world. Due to its heavy use in industry and daily life, such as food additives, cosmetics, pharmaceuticals, and paints, many residues are released into the environment and currently TiO2 nanoparticles are considered an emerging environmental contaminant. Although several studies have shown the effect of TiO2 nanoparticles on a wide range of organisms including bacteria, algae, plankton, fish, mice, and rats, little research has been performed on land plants. In this study, we investigated the effect of TiO2 nanoparticles on the growth, development, and gene expression of tobacco, an important economic and agricultural crop in the southeastern USA as well as around the world. We found that TiO2 nanoparticles significantly inhibited the germination rates, root lengths, and biomasses of tobacco seedlings after 3 weeks of exposure to 0.1, 1, 2.5, and 5 % TiO2 nanoparticles and that overall growth and development of the tobacco seedlings significantly decreased as TiO2 nanoparticle concentrations increased. Overall, tobacco roots were the most sensitive to TiO2 nanoparticle exposure. Nano-TiO2 also significantly influenced the expression profiles of microRNAs (miRNAs), a recently discovered class of small endogenous noncoding RNAs (similar to 20-22 nt) that are considered important gene regulators and have been shown to play an important role in plant development as well as plant tolerance to abiotic stresses such as drought, salinity, cold, and heavy metal. Low concentrations (0.1 and 1 %) of TiO2 nanoparticles dramatically induced miRNA expression in tobacco seedlings with miR395 and miR399 exhibiting the greatest fold changes of 285-fold and 143-fold, respectively. The results of this study show that TiO2 nanoparticles have a negative impact on tobacco growth and development and that miRNAs may play an important role in tobacco response to heavy metals/nanoparticles by regulating gene expression.