Genetic studies of transgenic rice plants overproducing an antibacterial peptide show that a high level of transgene expression did not cause inferior effects on host plants

Abstract

Overexpression of an oat thionin gene (Asthi1) confers enhanced disease resistance of rice (a cultivar “Chiyohonami”) against seed-transmitted phytopathogenic bacteria. The isolated paddy field test for evaluation of agronomic traits using T4 transgenic rice plants which are homozygous with a high level of Asthi1 protein has shown that transgenic rice possesses, in addition to enhanced anti-bacterial resistance, slight different characteristics compared with the original cultivar such as slight decrease in plant height, grain yield and simultaneity in heading behavior in addition to 2 days earlier in heading date. To address whether this difference was caused by ectopic high level expression of the transgene, T4 plants were back-crossed with wild-type and selfed, and the progenies were analyzed. Almost all characteristics observed in the field were found to be genetically segregated. While only a limited number of plants were used, the present findings indicate that the altered characteristics found in transgenic plants were not attributable to integration of Asthi1 transgene or its high expression itself, but instead to possible spontaneous mutations which may have occurred during in vitro culture for Agrobacterium-mediated transformation.