Azadirachtin-A
(AzaA) from the Indian neem tree (
Azadirachta indica
) has insecticidal properties;
however, its molecular mechanism
remains elusive. The “targeted and nontargeted proteomic profiling”,
metabolomics, matrix-assisted laser desorption/ionization time of
flight (MALDI-TOF) imaging, gene expression, and in silico analysis
provided clues about its action on
Helicoverpa armigera
. Fourth instar
H. armigera
larvae
fed on AzaA-based diet (AzaD) suffered from significant mortality,
growth retardation, reduced larval mass, complications in molting,
and prolonged development. Furthermore, death of AzaD-fed larvae was
observed with various phenotypes like bursting, blackening, and half-molting.
Liquid chromatography–mass spectrometry (LC–MS) data
showed limited catabolic processing of ingested AzaA and dramatic
alternations of primary metabolism in
H. armigera
. MALDI-TOF imaging indicated the presence of AzaA in midgut of
H. armigera
. In the gut, out of 79 proteins identified,
34 were upregulated, which were related to digestion, immunity, energy
production, and apoptosis mechanism. On the other hand, 45 proteins
were downregulated, including those from carbohydrate metabolism,
lipid metabolism, and energy transfer. In the hemolymph, 21 upregulated
proteins were reported to be involved in immunity, RNA processing,
and mRNA-directed protein synthesis, while 7 downregulated proteins
were implicated in energy transfer, hydrolysis, lipid metabolism,
defense mechanisms, and amino acid storage-related functions. Subsequently,
six target proteins were identified using labeled AzaA that interacted
with whole insect proteins. In silico analysis suggests that AzaA
could be efficiently accommodated in the hydrophobic pocket of juvenile
hormone esterase and showed strong interaction with active site residues,
indicating plausible targets of AzaA in
H. armigera
. Quantitative polymerase chain reaction analysis suggested differential
gene expression patterns and partly corroborated the proteomic results.
Overall, data suggest that AzaA generally targets more than one protein
in
H. armigera
and hence could be a
potent biopesticide.
