Premature polyadenylation contributes to the poor expression of the Bacillus thuringiensis cry3Ca1 gene in transgenic potato plants.

The cry genes that code for the insecticidal crystal proteins of Bacillus thuringiensis (B.t.) have been widely used to develop insect-resistant transgenic plants. The cry3Ca1 gene has been reported to code for a crystal protein which is particularly potent against the Colorado potato beetle (CPB). To explore the biotechnological potential of cry3Ca1, we introduced this gene into transgenic potato plants under the control of the CaMV 35S promoter. In the resulting transformants, the cry3-Ca1 gene was very poorly expressed. In fact, no full-length transcript (2300 nt) could be detected. Instead, only short transcripts of approximately 1100 nt were observed. Analysis of these short transcripts by Northern hybridization, RT-PCR as well as by cloning and sequencing showed that they resulted from premature polyadenylation. These processing events occurred at four sites within the cry3Ca1 coding region (at positions 652, 669, 914 and 981 relative to the translation start site). The sites at which premature polyadenylation took place were not those that showed the highest degree of identity to the canonical AAUAAA motif. Together with other recent data, our findings suggest that premature polyadenylation is an important mechanism which can contribute to the poor expression of transgenes in a foreign host.