Transmission of a Bacillus thuringiensis cry3Aa transgene from diploid to tetraploid potato using 4x-2x hybridization: effect of ploidy increase on transgene expression and implications for TPS hybrid production

Abstract

The study examined the effect of ploidy elevation through unreduced gametes on transgene expression in potato. Tetraploid transgenic progenies were obtained from one tetraploid potato cultivar crossed with 2n pollen producing diploid clones harbouring an exogenous transgene (cry3Aa). Both single- and multiple-insert diploid transgenic lines that were regenerated by Agrobacterium tumefaciens leaf disc inoculation were used in crosses. A DAS–ELISA system and no-choice feeding bioassay enabled characterization of the parental lines as either 'high' or 'low' expressers of the Cry3Aa protein. High Cry3Aa expression was observed for both single-insert transgenic diploids and their 4x–2x progeny. On the contrary, 68% of 4x–2x progeny derived from a multiple-insert, diploid transgenic had significantly reduced Cry3Aa expression compared with the parent, with 32% demonstrating nearly complete silencing of the transgene. Multiple copies of a transgene, like homologous native genes, may be susceptible to transgene silencing following polyploidization. Therefore, incorporation of exogenous transgenes into a true potato seed (TPS) production system is feasible if a single-insert diploid parent is used. Gene-centromere mapping of the cry3Aa transgene demonstrated that a non-transgenic refuge might be naturally created in a TPS hybrid system through genetic recombination.