Deciphering the tomato defense network againstHelicoverpa armigera: From transcriptional reprogramming to biochemical changes.

Abstract

Helicoverpa armigera (Hübner) is able to feed on more than 280 host plants; however, the mechanisms that allow it to persist on such a wide range of hosts may involve transcriptional reprogramming and biochemical alternations which are still not well understood. Therefore, we analyzed the transcriptional responses of salicylic acid (SA)- and jasmonic acid (JA)-mediated signaling pathways in tomato (Solanum lycopersicum L.), which is increasingly used as a model plant system. The SA-related genes PR1a and PAL showed increased expression both locally and systemically at 12, 24, 36, and 48  h post-infestation (HPI). In contrast, the JA-associated transcripts PIN2 and LOX did not show induction and were even suppressed at 48 HPI. An oxidative burst of H2O2 was detected, which subsequently activated antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) at 2, 5, 12, 24, and 48 HPI. The levels of phenolic compounds increased markedly, and the concentration of soluble proteins also showed noticeable changes. Larval weight of H. armigera declined at 3, 5, and 7  days post-infestation (DPI) when plants were treated with exogenous BTH (Benzothiadiazole) and MeJA (Methyl Jasmonate). The 0.25  mM MeJA resulted in a significantly greater reduction compared with 0.5  mM BTH. These findings suggest that activation of the JA pathway is unfavorable for H. armigera, whereas the insect may survive on diverse hosts by promoting SA signaling pathway. H. armigera-mediated defense network was also constructed. Such insights may contribute to the development of safer pest management techniques and insect-resistant crops against polyphagous pests.