Influence of plant development and environment on transgene expression in potato and consequences for insect resistance

Clonal replicates of different transformed potato plants expressing transge ne constructs containing the constitutive Cauliflower Mosaic Virus (CaMV) 3 5S promoter, and sequences encoding the plant defensive proteins snowdrop l ectin (Galanthus nivalis agglutinin; GNA), and bean chitinase (BCH) were pr opagated in tissue culture. Plants were grown to maturity, at first under c ontrolled environmental conditions, and later in the glasshouse. For a give n transgene product, protein accumulation was found to vary between the dif ferent lines of clonal replicates (where each line was derived from a singl e primary transformant plant), as expected. However, variability was also f ound to exist within each line of clonal replicates, comparable to the vari ation of mean expression levels observed between the different clonal lines . Levels of GNA, accumulated in different parts of a transgenic potato plan t, also showed variation but to a lesser extent than plant-plant variation in expression. With the majority of the clonal lines investigated, accumula tion of the transgene product was found to increase as the potato plant dev eloped, with maximum levels found in mature plants. The variation in accumu lation of GNA among transgenic plants within a line of clonal replicates wa s exploited to demonstrate that the enhanced resistance towards larvae of t he tomato moth, Lacanobia oleracea L., caused by expression of this protein in potato, was directly correlated with the level of GNA present in the pl ants, and that conditions under which the plants were grown affect the leve ls of GNA expression and subsequent levels of insect resistance.