Low selenium increases the auxin concentration and enhances tolerance to low phosphorous stress in tobacco

Selenite is the predominant form of selenium (Se) available to plants in soils, which is uptake by inorganic phosphate (Pi) transporters. Previous studies have suggested that selenite might affect plants' growth and development, but the molecular mechanisms connecting Pi, Se, and auxin functions are still unclear. Here, we show that Se is involved in auxin and phosphate starvation responses in tobacco (Nicotiana tabacum). Low Se (1 mg L-1) addition increased the biomass and changed the architecture of tobacco root (increased primary root length and the number of lateral roots) compared to control treatments without adding Se, and Se treated plants also had higher auxin concentrations, possibly as a result of the increased expression of auxin synthesis genes and auxin efflux carriers. Moreover, low Se (1 mg L-1) enhanced tolerance to low Pi stress, and the over expression of NtPT2 in tobacco increased its total P and Se contents under Pi-sufficient conditions. These data revealed there is an interactive mechanism among Pi, Se and auxin acting upon plant growth, and provide a potential candidate gene (NtPT2) for breeding Se-enriched tobacco plants.