Inheritance and expression of Cry3Aa and PVY-O coat protein transgenes in diploid and tetraploid potato

Transgenic resistance to plant pathogens and insect pests, although temporarily on hold for potato because of political reasons, offers promise for the future of both asexually and sexually propagated potato. For a system that exploits both true potato seed (TPS) and transgenic resistance, factors that affect transgene expression during and after gametogenesis must be understood. Gene silencing is an epigenetic phenomenon affecting transgene expression that may be influenced by the parent-of-origin of a transgene. Using PCR to determine transgene segregation, and ELISA to determine transgene expression in reciprocal crosses of tetraploid potato lines, one of which carried the Cry3Aa gene as a single insert, we found that expression levels of progeny bearing the transgene did not differ. However, in crosses between transgenic Atlantic and wild type Katahdin plants, the ratio of expressers to nonexpressers varied significantly between reciprocals and differed significantly from the expected 1:1 segregation ratio (n=70, χ2=8.2). A lack of variation in transgene expression indicated that there was no parent of origin effect in the reciprocal progeny tested. An excess of transgenic progeny when the Cry3Aa gene was maternally inherited suggests differential gametic selection or an epigenetic effect on transgene expression during megagametogenesis and/or pollination and fertilization.