Marker-free, tissue-specific expression of Cry1Ab as a safe transgenic strategy for insect resistance in rice plants

Abstract

Background: Rice is the major food resource for nearly half of the global population; however, insect infestation could severely affect the production of this staple food. To improve rice insect resistance and reduce the levels of Bt toxin released into the environment, the Cry1Ab gene was conjugated to the rice rbcS promoter to express Bt toxin in specific tissues of transgenic plants.

Results: Eight marker-free, T(2) lines were separated from the T(0) cotransformants. Using RT-PCR, high levels of Cry1Ab expression were detected in the leaf but not in the seed. The Cry1Ab protein level ranged from 1.66 to 3.31 µg g(-1) in the leaves of four transgenic lines, but was barely detectable in their seeds by ELISA. Bioassays showed that the mortality rate of silkworm larvae feeding on mulberry leaves dipped in transgenic rice flour and pollen was less than that of the positive control (KMD), and that their average weight was higher than that of KMD, suggesting that the Cry1Ab protein was not expressed in the seed and pollen.

Conclusion: The transgene conferred a high level of resistance to insects and biosafety to the rice plants, which could be directly used in rice breeding.