Poster: Plant Insect/Nematode Interactions

Abs # 681: Overexpression of Polyphenol Oxidase in Transgenic Tomato Plants Increase Resistance to Common Cutworm (Spodoptera litura (F.))

Presenter:	Thipyapong, Piyada , piyada@ccs.sut.ac.th
Authors	Thipyapong, Piyada  (A)   Mahanil, Siraprapa  (A)   Attajarusit, Jutharat  (A)   Steffens, John C. (B)
Affiliations:	(A): Suranaree University of Technology (B): Syngenta Biotechnology, Inc.

Polyphenol oxidases (PPOs), catalyzing the oxidation of phenolics to quinones, have been previously reported to play a defensive role against Pseudomonas syringae and assumed to be involved in insect resistance. To assess the impact of PPO expression on resistance to common cutworm (Spodoptera litura (F.)), we used transgenic tomato plants constitutively expressing sense- and antisense-oriented potato PPO genes. The transgenic plants expressing a sense PPO construct exhibited 5- to 10-fold higher PPO activity levels whereas the antisense PPO transgenic plants exhibited 15- to 40- fold lower PPO activity levels than nontransformed controls. The growth rates of common cutworm larvae feeding on leaflets at node 8 of antisense PPO plants were 3 and 3.9 times higher than growth rates of those feeding on nontransformed control and PPO-overexpressing transgenic plants, respectively. In contrast, the PPO-overexpressing transgenic plants showed an increase in resistance to common cutworm; 1.3 times lower larval growth rates than controls. The amount of foliage consumed was negatively correlated with PPO activity levels. In addition, increased PPO activity led to higher larval mortality. The percent mortality of larvae feeding on antisense PPO, control and PPO-overexpressing leaves were 0%, 16% and 52%, respectively. These results suggest a critical role of PPO-mediated phenolic oxidation in insect resistance.