The accumulation of recombinant miraculin is independent of fruit size in tomato.

The taste-modifying protein miraculin (MIR) has received increasing interest as a new low-calorie sweetener. In our previous study using the tomato variety 'Micro-Tom,' it was shown that in transgenic tomatoes in which was expressed by using the promoter () and a terminator () cassette (), higher levels of miraculin accumulated than when was driven by the terminator () cassette (). 'Micro-Tom' is a dwarf tomato used for research and shows a low yield. To achieve high productivity of MIR, it is essential to improve the MIR accumulation potential by using high-yielding cultivars. In this study, we evaluate whether the high MIR accumulation trait mediated by the appears even when fruit size increases. A line in which the cassette was introduced into a high-yielding variety was bred by backcrossing. The line homozygous for showed higher accumulation of MIR than the heterozygous line. Despite large differences in fruit size, the MIR level in the backcross line was similar to that in the line (background 'Micro-Tom'). It was approximately 3.1 times and 4.0 times higher than those in miracle fruits and the tomato line 5B ('Moneymaker' background, which exhibits the highest miraculin productivity achieved thus far), respectively. These results demonstrate that the high MIR accumulation trait mediated by the appears even when fruit size is increased.