Beyond Bacillus thuringiensis: New insecticidal proteins with potential applications in agriculture

Future biotech crops to control agriculturally relevant insects require new modes of action (MoAs) to counter acquired insect resistance or new pest emergence. A new MoA must entail a new “site of action” (SoA) as resistance to insecticidal proteins can involve alteration in the binding site or receptor, a key MoA determinant of insect resistance traits and foundational to discovery of useful new proteins. Bacillus thuringiensis (Bt) has provided nearly all successfully deployed crop incorporated insect protectants, but it has become increasingly difficult to identify new proteins with utility for agricultural applications. Researchers have increasingly turned to ‘non-Bt’ sources that span the biosphere. In this chapter, we present some key insecticidal protein discoveries from bacteria, fungi and plants with differing degrees of promise. These proteins come from a variety of protein structural families, some similar to those identified from Bt, while others are only remotely related and novel. From bacteria, we feature PIP-47Aa (novel), IPD072Aa (novel), AfIP-1A/AfIP-1B (aegerolysin/resembles membrane attack complex perforin-like; MACPF), Mpf2Ba1 (MACPF) and Mpf3Aa1 (MACPF), and from fungi we feature several aegerolysin/MACPF binary proteins. From plants, we cover candidates from lower plants, particularly ferns and lycophytes, drawing a contrast to largely unsuccessful efforts sourcing efficacious genes from higher plants. We feature: Tma12 (AA10 lytic polysaccharide monooxygenases), IPD083 (novel) and the PtIP-50/PtIP-65 binary pair (novel/aerolysin), IPD079 (MACPF), and IPD113 (δ-endotoxin-like). These lower plant discoveries exhibit interesting parallels with microbial insecticidal proteins. From these examples, it becomes clear that non-Bt organisms are rich in proteins with promise for biotech development.