Overexpression of tomato polyphenol oxidase increases resistance to common cutworm

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Polyphenol oxidases (PPOs), which catalyze the oxidation of phenolics to quinones, have been reported to confer resistance to Pseudomonas syringae and are thought to be involved in insect resistance. To assess the impact of PPO expression on resistance to the common cutworm (Spodoptera litura (F.)) (Lepidoptera: Noctuidae), we used transgenic tomato (Lycopersicon esculentum Mill.) plants constitutively expressing sense- and antisense-oriented potato PPO genes. Transgenic plants expressing a sense PPO construct (overexpressing PPO [OP] plants) exhibited 2.0-5.7-fold higher PPO activity levels, whereas antisense PPO transgenic plants (suppressed PPO [SP] plants) exhibited 1.5-7.3-fold lower PPO activity levels than nontransformed controls. The PPO-overexpressing transgenic plants clearly showed an increase in resistance; simple growth rates of common cutworms on OP plants were up to 2.5 and 3.3 times lower than on controls and SP leaves, respectively, and larvae consumed less foliage. In addition, increased PPO activity led to higher larval mortality. The efficiency of conversion of ingested food and efficiency of conversion of digested food of third instars were found to be significantly different among tomato genotypes with differing PPO activity levels, suggesting that PPO activity rendered foliage less nutritious. Moreover, when leaflets at nodes 4 and 8 of SP, NT and OP plants were detached and fed to common cutworm larvae, their PPO activity levels were induced 1.6-2.2-fold. These results suggest a critical role for PPO-mediated phenolic oxidation in resistance to this insect. Manipulation of PPO activity could provide resistance simultaneously to both disease and insect pests, and therefore might be used as a component of effective integrated pest management. © 2008 Elsevier Ireland Ltd. All rights reserved.

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Plant Science

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