New gene construction strategy in T-DNA vector to enhance expression level of sweet potato sporamin and insect resistance in transgenic Brassica oleracea.

Sporamin, an abundant storage protein in tuberous roots of sweet potato, possesses strong inhibitory activity against trypsin and pest-resistance. To promote consistent high-level expression of sporamin and insect resistance in transgenic Brassica plants, a wound-responsive sporamin promoter (Pspoa) alone or combined with matrix-attached-region-like DNA segment (spoMAR) were constructed for driving sporamin cDNA. The results showed the transgenic plants containing Pspoa-drived sporamin and spoMAR displayed the highest level and low inter-transformant variability of sporamin expression, and the ability of insect resistance of transformants positively correlated with sporamin activity. Furthermore, expressions of Pspoa-drived sporamin especially combined with the spoaMAR retains high and steady levels in the T(1) and T(2) generations, in marked contrast to the variable expression patterns observed in CaMV35S promoter-driven transformants. This study evidently indicates that the Pspoa and spoaMAR would be very efficient for high transgene expression in plants and obtaining inherently stable transformants in consecutive progenies.