Titanium Dioxide Nanoparticles Promote Root Growth by Interfering with Auxin Pathways in Arabidopsis thaliana

TiO_(2) nanoparticles(nano-TiO_(2))are widely used in the world,and a considerable amount of nano-TiO_(2) is released into the environment,with toxic effects on organisms.In the various species of higher plants,growth,including seed germination,root elongation,and biomass accumulation,is affected by nano-TiO_(2).However,the underlying molecular mechanisms remain to be elucidated.In this study,we observed that nano-TiO_(2) promoted root elongation in a dose-dependent manner.Furthermore,we found that nano-TiO_(2) elevated auxin accumulation in the root tips of the auxin marker lines DII-VENUS and DR5::GUS,and,correspondingly,quantitative real-time PCR analysis revealed that nano-TiO_(2) increased the expression levels of auxin biosynthesis-and transport-related genes.GFP fluorescence observation using transgenic PIN2-GFP indicated that nano-TiO_(2) promoted root growth by inducing PIN2 accumulation.Thus,we propose that nano-TiO_(2) promote root growth in Arabidopsis thaliana by altering the expression levels of auxin biosynthesis-and transport-related genes.