The HSP Terminator of Arabidopsis thaliana Induces a High Level of Miraculin Accumulation in Transgenic Tomatoes

High-level accumulation of the target recombinant protein is a significant issue in heterologous protein expression using transgenic plants. Miraculin, a taste-modifying protein, was accumulated in transgenic tomatoes using an expression cassette in which the miraculin gene was expressed by the cauliflower mosaic virus (CaMV) 35S promoter and the heat shock protein (HSP) terminator (MIR-HSP). The HSP terminator was derived from heat shock protein 18.2 in Arabidopsis thaliana. Using this HSP-containing cassette, the miraculin concentration in T0 transgenic tomato lines was 1.4–13.9% of the total soluble protein (TSP), and that in the T1 transgenic tomato line homozygous for the miraculin gene reached 17.1% of the TSP. The accumulation level of the target protein was comparable to levels observed with chloroplast transformation. The high-level accumulation of miraculin in T0 transgenic tomato lines achieved by the HSP terminator was maintained in the successive T1 generation, demonstrating the genetic stability of this accumulation system.