Gene dosage and genetic background affect miraculin accumulation in transgenic tomato fruits

Gene dosage and genetic background are factors that influence transgene expression in transgenic plants. In our previous studies, we produced transgenic tomato plants that accumulate miraculin, a taste-modifying protein, in a genetically stable manner. To elucidate the effects of gene dosage and genetic background on miraculin accumulation in transgenic tomato fruits, we generated hybrid tomato lines between the homozygous transgenic line 56B (background cultivar 'Moneymaker') and the pure cultivars 'Micro-Tom,' 'Moneymaker,' 'Ailsa Craig,' 'M82,' 'Rutgers' and 'Aichi-first' and analyzed them for miraculin mRNA expression and miraculin protein accumulation. The hybrid lines exhibited variation in their fruit structures. Among the hybrid lines heterozygous for the miraculin gene, miraculin accumulation in the fruits varied from 111.0 mu g g(-1) fresh weight (FW) to 159.4 mu g g(-1) FW. Furthermore, the homozygous line 56B showed higher miraculin accumulation and miraculin mRNA expression than the heterozygous line 56B x 'Moneymaker.' These results demonstrate the profound effects of gene dosage and genetic background on miraculin accumulation in transgenic tomato fruits.