Functional Characterization Of The SbNrat1 Gene In Sorghum

Aluminum toxicity is a primary limitation for crop production on acid soils,which comprise about 40%of the world's potentially arable land.When the pH of soils is below 5,the aluminum will become soluble AL3+,which will poison the root of the plant at micromolar concentrations.Besides,AL3+ concentration will continue to increase with the drop of pH.Aluminum toxicity can inhibit the growth of the roots,shortening the roots and making them thicker,thus affecting absorption of mineral elements and water.Finally Aluminum toxicity might limit the growth of aerial parts.Therefore,understanding genes and mechanisms of plant aluminum tolerance has important implications for crop growth in acid soil areas.There is a wide variation in the tolerance to A1 toxicity between species and cultivars within a species.Species or cultivars with high Al tolerance have evolved various strategies to detoxify Al externally and/or internally.Japonica cultivars of rice show superior Al tolerance under both field and hydroponic conditions.Genetic and molecular analysis showed that high Al tolerance in rice is likely achieved by multiple genes and mechanisms at different cellular level.OsNrat1(OsNramp4)which is located on the plasma membrane cooperates with OsALSl localized on the vacuolar membrane for the internal detoxification mechanism of rice.The Natural Resistance Associated Macrophage Protein(NRAMP)members play diverse roles in metal transport in plants.Recent studies have showed that OsNratl(OsNra,mp4)encodes an A1 transporter,which is required for rice Al tolerance.In this study,we functionally characterized a NRAMP member in sorghum,SbNratl,which is homologous to OsNratl with 88%identity.SbNratl was expressed in both roots and shoots,and its expression was not induced by Al treatment.Transient expression of SbNratl fused with GFP showed that SbNratl was localized to the plasma membrane.When expressed in yeast,SbNratl transports trivalent Al ion,but not Mn and Cd.Furthermore,introduction of SbNratl into the rice mutant osnratl can rescue its sensitivity to Al.However,no correlation between Al tolerance and the expression level of SbNratl was found in thirteen sorghum cultivars tested.These results indicate that SbNratl functions as an Al transporter that is possibly involved in basic Al tolerance in sorghum.