Accumulation of Cry1Ab/Ac proteins released from transgenic Bt-rice in the rhizosphere of a paddy soil

By cultivating transgenic crops engineered with cry genes encoding insecticidal proteins (Cry-proteins or Bt-toxins) from Bacillus thuringiensis (Bt), Cry-proteins could be released into the agricultural soil ecosystem. This study was aimed to monitor rice root development along with Cry-protein production within Bt-rice and to analyze spatial and temporal distribution of Cry-proteins in the rhizosphere soil. Transgenic Bt-rice and its isogenic non-Bt-rice cultivar were cultivated in rhizotron boxes. Scanning and subsequent image analysis allowed the display of root development and redoximorphic features. Cry-proteins were analyzed with an ELISA assay after spatiotemporal soil sampling. Cry1Ab/Ac protein continuously produced within plant tissue of Bt-rice and could be released via root exudates during growth. The distribution and amount of Cry1Ab/Ac proteins were root-oriented as the protein amount in rhizotrons decreased with increasing distance to rice roots. In addition, Cry-protein distribution correlated with redox features by showing much higher amount of proteins in oxidized soil material than the reduced. A successive growth period showed same trends in the distribution of Cry-protein but on a higher level, as was related to a background concentration of Cry-proteins, resulting from the initial cultivation of transgenic rice cultivars. We could clearly show that Cry-proteins are persistent in the rhizosphere and that more attention should be payed to their fate especially in complex and dynamic soil ecosystems such as paddy soils.