Abstract
The first generation transgenic crops used strong constitutive promoters for transgene expression. However, tissue-specific expression is desirable for more precise targeting of transgenes. Moreover, piercing/sucking insects, which are generally resistant to insecticidal Bacillus thuringiensis (Bt) proteins, have emerged as a major pests since the introduction of transgenic crops expressing these toxins. Phloem-specific promoters isolated from Banana bunchy top virus (BBTV) were used for the expression of two insecticidal proteins, Hadronyche versuta (Blue Mountains funnel-web spider) neurotoxin (Hvt) and onion leaf lectin, in tobacco (Nicotiana tabacum). Here we demonstrate that transgenic plants expressing Hvt alone or in combination with onion leaf lectin are resistant to Phenacoccus solenopsis (cotton mealybug), Myzus persicae (green peach aphids) and Bemisia tabaci (silver leaf whitefly). The expression of both proteins under different phloem-specific promoters resulted in close to 100% mortality and provided more rapid protection than Hvt alone. Our results suggest the employment of the Hvt and onion leaf lectin transgenic constructs at the commercial level will reduce the use of chemical pesticides for control of hemipteran insect pests.
Highlights
Most conventional neurotoxic pesticides[26,27,28]
RSs1 has already been used to regulate the expression of β-glucuronidase (GUS)[33], Galanthus nivalis agglutinin (GNA)[34,35], and Allium sativum leaf agglutinin (ASAL)[36] in a phloem-specific manner
Banana bunchy top virus BBTV, the type member of the genus Babuvirus in the family Nanoviridae, has a phloem-limited nature[40]. This virus, which is transmitted by the green peach aphid (Myzus persicae), has a multipartite genome consisting of six circular ssDNAs, individually encapsulated within separate icosahedral virions
Summary
Most conventional neurotoxic pesticides[26,27,28]. A variety of long-term strategies are being developed to avoid the development of insect resistance to Bt toxins. As many hemipteran insects feed exclusively from the phloem, effective resistance to these insects can be limited to the phloem cells by expressing genes under phloem-specific promoters. Using this approach, the expression of resistance genes in non-target parts and tissues can be avoided, thereby reducing the metabolic load on the transgenic plants. The most important constituents of many spider venoms are 4–10 kDa ligand peptides that are tightly folded by means of intramolecular disulfide bridges, and which include a great diversity of antagonists acting on membrane ion channels[48,49] Some of these peptides have the ability to block ion channels at the neuronal level. In feeding experiments with the chewing herbivores H. armigera and Spodoptera littoralis (Egyptian cotton leafworm), insects on transgenic plants expressing Hvt from the 35S promoter were dead within 24 h53–56
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