The 35S promoter used in a selectable marker gene of a plant transformation vector affects the expression of the transgene

Positive selection of transgenic plants is essential during plant transformation. Thus, strong promoters are often used in selectable marker genes to ensure successful selection. Many plant transformation vectors, including pPZP family vectors, use the 35S promoter as a regulatory sequence for their selectable marker genes. We found that the 35S promoter used in a selectable marker gene affected the expression pattern of a transgene, possibly leading to a misinterpretation of the result obtained from transgenic plants. It is likely that the 35S enhancer sequence in the 35S promoter is responsible for the interference, as in the activation tagging screen. This affected expression mostly disappeared in transgenic plants generated using vectors without the 35S sequences within their T-DNA region. Therefore, we suggest that caution should be used in selecting a plant transformation vector and in the interpretation of the results obtained from transgenic approaches using vectors carrying the 35S promoter sequences within their T-DNA regions.