Identification and validation of HaGNA gene as potential RNAi target for management of Old-World bollworm Helicoverpa armigera (Hübner).

BACKGROUND: The chitin biosynthesis pathway represents an important molecular target for the development of sustainable insect pest management strategies. In this pathway, glucosamine-6-phosphate N-acetyltransferase (HaGNA) catalyzes a key upstream acetylation step required for the generation of precursors for chitin synthesis. However, the functional role of this gene in the globally important pest Helicoverpa armigera remains unexplored. METHODS AND RESULTS: In the present study, HaGNA was identified, cloned and functionally validated using RNA interference (RNAi). In vitro synthesized dsRNA targeting HaGNA gene was administered through injection. Growth, developmental and wing morphometric observations were recorded coupled with analysis of chitin content and gene down regulation. Expression analysis revealed its constitutive expression across developmental stages and tissues, with elevated transcript levels in the head, midgut, egg and pupal stages, indicating an important role of HaGNA in growth and metamorphosis. RNAi-mediated knockdown of HaGNA in larval stages resulted in a a modest but statistically significant 30.12% reduction in transcript abundance following primary dsRNA injection, accompanied by a 25.40 ± 5.03% decrease in chitin content. Knockdown of HaGNA induced severe developmental abnormalities, including incomplete ecdysis, cuticular deformities, larval-pupal intermediates, pupal rupture and impaired adult emergence. Treated insects showed poor weight gain in larva and pupa, prolonged pupal duration and cumulative mortality of 73.33 ± 3.85%. In addition, more than 55% of emerging adults exhibited severe wing deformities, with wing length reductions of 25.81-39.25%, indicating disrupted metamorphic remodeling and cuticular integrity. CONCLUSIONS: Overall, these findings demonstrate the multifaceted roles of HaGNA in chitin metabolism, metamorphosis, wing development and survival of H. armigera.