Stability and tissue-specific Cry10Aa overexpression improves cotton resistance to the cotton boll weevil

Abstract

The cotton boll weevil (CBW, Anthonomus grandis) is the most destructive cotton insect pest affecting cotton crops. To overcome this problem, CBW-resistant genetically modified cotton plants overexpressing Bacillus thuringiensis entomotoxins were successfully obtained. Previous results showed that the overexpression of Cry10Aa protoxin led to high mortality of the CBW larvae in greenhouse conditions. In this study, we advanced three more generations (T2 to T4), with several cotton events constitutively overexpressing the Cry10Aa protoxin, and the transgene stability and agronomic performance were investigated. In addition, stable transgenic cotton overexpressing the Cry10Aa active (Cry10Aa protoxin lacking the α-helix N-terminal) driven by cotton flower bud-specific promoters were generated and characterized. Cotton events constitutively or tissue-specifically overexpressing the Cry10Aa protein (protoxin or active) represented mortality percentages of the CBW larva of up to 85 % in plants under greenhouse conditions. Events overexpressing the Cry10Aa active under control of the flower bud-specific promoter showed higher protein accumulation in stamens and carpels compared to the events with constitutive expression. Our findings suggested that the high stability of the Cry10Aa transgene and the elevated expression level and protein accumulation in flower bud tissues (primarily in stamen and carpels) contribute to improved resistance to CBW larvae. Finally, some notable events were selected with potential for future field trials in different cotton-producing regions of Brazil. Therefore, cotton events overexpressing high levels of the Cry10Aa protein in flower bud tissue may have a strong potential for commercial use in the integrated management of CBW.