Practice question

Search for effective protease inhibitor for transgenic resistance identified cowpea trypsin inhibitor as potent candidate due to broad activity against lepidopteran gut proteases and stability in alkaline environment. Cowpea Vigna unguiculata seeds accumulate defense proteins to protect against storage pests. Gene CpTI encoding 80 amino acid inhibitor with two disulfide bridges isolated from developing seeds and placed under CaMV 35S promoter. Tobacco transformed with CpTI exhibited 2 to 5 percent soluble protein as inhibitor, reducing tryptic activity of Heliothis virescens midgut extracts and causing 50 percent reduction in larval weight gain in feeding bioassays. Compared to soybean Kunitz inhibitor, CpTI showed enhanced resistance to proteolytic degradation due to compact structure. Field trials of transgenic tobacco and later cotton combining CpTI with cry1Ab demonstrated reduced bollworm damage. Hence cowpea provides source of trypsin inhibitor gene utilized in early proteinase inhibitor mediated insect control strategies complementing Bacillus thuringiensis approach in transgenic plant development history. Development involved Agrobacterium mediated transformation with nptII marker and analysis of T1 progeny for Mendelian segregation of inhibitor activity. Resistance level correlated with inhibitor expression dose, illustrating quantitative relationship between defensive protein accumulation and insect growth inhibition in transgenic tobacco lines.