Plant Plastid Engineering

Wani, Shabir H.; Haider, Nadia; Kumar, Hitesh; Singh, N.B.

Over-expression of the cry2Aa2 operon in plastids was proved effective in allowing a broad-spectrum of protection against a range of pests [81] . In cabbage, the cry1Ab gene was also successfully transferred into the plastid genome [85] . Expression of cry1Ab protein was detected in the range of 4.8-11.1% of total soluble protein in transgenic mature leaves of the two species. Insecticidal effects on Plutella xylostella were also demonstrated in cry1Ab transformed cabbage. In an attempt to increase insect resistance in trans-genic rice plants, a synthetic truncated cry1Ac gene was linked to the rice rbcS promoter and its transit peptide sequence (tp) for plastid-targeted expression [86] . Use of the rbcS-tp sequence increased the cry1Ac transcript and protein levels by 25-and 100-fold, respectively, with the accumulated protein in plastids comprising up to 2% of the total soluble proteins. The high level of cry1Ac expression resulted in high levels of plant resistance to three common rice pests, rice leaf folder, rice green caterpillar, and rice skipper, as evidenced by insect feeding assays. It was concluded that targeting of cry1Ac protein to the plastid using the rbcS:tp system confers a high level of plant protection to insects. Several other cry proteins have also been expressed in plastids of tobacco [83, 84, 87, 88] and rice [50] (see Table 2 ).