Selenium Modulates the Level of Auxin to Alleviate the Toxicity of Cadmium in Tobacco.

Cadmium (Cd) is an environmental pollutant that potentially threatens human health worldwide. Developing approaches for efficiently treating environmental Cd is a priority. Selenium (Se) plays important role in the protection of plants against various abiotic stresses, including heavy metals. Previous research has shown that Se can alleviate Cd toxicity, but the molecular mechanism is still not clear. In this study, we explore the function of auxin and phosphate (P) in tobacco (Nicotiana tabacum), with particular focus on their interaction with Se and Cd. Under Cd stress conditions, low Se (10 µM) significantly increased the biomass and antioxidant capacity of tobacco plants and reduced uptake of Cd. We also measured the auxin concentration and expression of auxin-relative genes in tobacco and found that plants treated with low Se (10 µM) had higher auxin concentrations at different Cd supply levels (0 µM, 20 µM, 50 µM) compared with no Se treatment, probably due to increased expression of auxin synthesis genes and auxin efflux carriers. Overexpression of a high affinity phosphate transporter NtPT2 enhanced the tolerance of tobacco to Cd stress, possibly by increasing the total P and Se content and decreasing Cd accumulation compared to that in the wild type (WT). Our results show that there is an interactive mechanism among P, Se, Cd, and auxin that affects plant growth and may provide a new approach for relieving Cd toxicity in plants.

Modelling pollen-mediated gene flow in rice: risk assessment and management of transgene escape.

Fast development and commercialization of genetically modified plants have aroused concerns of transgene escape and its environmental consequences. A model that can effectively predict pollen-mediated gene flow (PMGF) is essential for assessing and managing risks from transgene escape. A pollen-trap method was used to measure the wind-borne pollen dispersal in cultivated rice and common wild rice, and effects of relative humidity, temperature and wind speed on pollen dispersal were estimated. A PMGF model was constructed based on the pollen dispersal pattern in rice, taking outcrossing rates of recipients and cross-compatibility between rice and its wild relatives into consideration. Published rice gene flow data were used to validate the model. Pollen density decreased in a simple exponential pattern with distances to the rice field. High relative humidity reduced pollen dispersal distances. Model simulation showed an increased PMGF frequency with the increase of pollen source size (the area of a rice field), but this effect levelled off with a large pollen-source size. Cross-compatibility is essential when modelling PMGF from rice to its wild relatives. The model fits the data well, including PMGF from rice to its wild relatives. Therefore, it can be used to predict PMGF in rice under diverse conditions (e.g. different outcrossing rates and cross-compatibilities), facilitating the determination of isolation distances to minimize transgene escape. The PMGF model may be extended to other wind-pollinated plant species such as wheat and barley.

Dramatic reduction of crop-to-crop gene flow within a short distance from transgenic rice fields.

Genetically modified (GM) rice with enhanced agronomic traits and pharmaceutical uses are ready for widespread adoption. Little is known about isolation requirements for achieving stringent transgene confinement in rice. To investigate the extent of pollen-mediated crop-to-crop transgene flow, we conducted a field experiment with four plot-size treatments of adjacent GM and nonGM rice (Oryza sativa) in China. Three insect-resistant GM rice (Bt/CpTI) and nonGM isogenic lines were used in the study. The hygromycin-resistance transgene (hpt) marker was used to screen seeds from the nonGM rice rows at different distance intervals from GM rice plots. Based on the examination of > 2.1 million germinated seeds, we found a dramatic reduction in transgene frequencies with increasing distance from the GM crop, ranging from c. 0.28% at 0.2 m to < 0.01% at 6.2 m. In addition, different plot size did not significantly affect the frequencies of gene flow. In conclusion, pollen-mediated crop-to-crop transgene flow in rice can be maintained at negligible levels with short spatial isolation. The model can also be applied to other crops with self- and wind-pollination.