Gene silencing in potato: allelic differences and effect of ploidy

Silencing of genes is mostly studied in diploid, homozygous, self-fertile a nd sexually propagated species. However, conclusions drawn for these specie s are not always applicable to crops like potato, which is an autotetraploi d, highly heterozygous, vegetatively propagated species. Factors influencin g the level of silencing in potato are discussed, with emphasis on inhibiti on of the granule-bound starch synthase I (GBSSI) gene. Type of construct, number of integrated T-DNA copies, structural arrangement of the T-DNA locu s, integration site, target tissue and genetic background are important fac tors for all plant species. Ploidy level and multiple allelism are factors deserving special attention when the efficiency of silencing of endogenous genes is studied in polyploid, heterozygous species such as potato.