Transgenic sugarcane plants expressing high levels of modified cry1Ac provide effective control against stem borers in field trials

To improve transgene expression level, we synthesized a truncated insecticidal gene m-cry1Ac by increasing its GC content from 37.4 to 54.8%, based on the codon usage pattern of sugarcane genes, and transferred it into two sugarcane cultivars (ROC16 and YT79-177) by microprojectile bombardment. The integration sites and expression pattern of the transgene were determined, respectively, by Southern, northern and western blot analyses. The transgenic sugarcane lines produced up to 50 ng Cry1Ac protein per mg soluble proteins, which was about fivefold higher than that produced by the partially modified s-cry1Ac (GC% = 47.5%). In greenhouse plant assay, about 62% of the transgenic lines exhibited excellent resistance to heavy infestation by stem borers. In field trials, the m-cry1Ac transgenic sugarcane lines expressing high levels of Cry1Ac were immune from insect attack. In contrast, expression of s-cry1Ac in transgenic sugarcane plants resulted in moderately decreased damages in internodes (0.4-1.7%) and stalks (13.3-26.7%) in comparison with the untransformed sugarcane controls, which showed about 4 and 26-40% damaged internodes and stalks, respectively. Significantly, these transgenic sugarcane lines with high levels of insect resistance showed similar agronomic and industrial traits as untransformed control plants. Taken together, the findings from this study indicate a promising potential of engineering an insect-resistant gene to tailor its protein expression levels in transgenic sugarcane to combat insect infestations.