Expression analysis of the polyphenol oxidase gene in response to signaling molecules, herbivory and wounding in antisense transgenic tobacco plants.

KEY MESSAGE: We provide evidence that the expression of the PPO gene was significantly reduced in response to wounding, MeJ and herbivory in transgenic tobacco under wound-inducible OsRGLP2 promoter in an anti-sense orientation. ABSTRACT: Polyphenol oxidase (PPO) genes play an important role in plant defense mechanisms against biotic and abiotic stresses. In the present study, a 655 bp core sequence of the potato PPO gene was placed under the control of wound-inducible OsRGLP2 promoter in an anti-sense direction to evaluate its potential effects during biotic (Trialeurodes vaporariorum's infestation) and various abiotic (wounding, MeJ, ABA) stresses. Transcriptional profiling of PPO gene by real-time PCR (qRT-PCR) in transgenic tobacco revealed a significant suppression (3.5-fold) of PPO in response to wounding than control plants after 24 h. In response to MeJ at different concentrations (100 µM and 200 µM), the PPO expression was greatly down-regulated by 4.7-fold after 6 h at 100 µM MeJ, and a non-significant expression was observed with ABA treatment. Moreover, significant levels of PPO reduction (sixfolds) was found in whitefly feeding assay indicating that expression of potato PPO in an anti-sense orientation had down-regulated the PPO activity. This down-regulation of PPO by wounding, MeJ and whitefly infestation clearly links the specific expression of PPO in biotic and abiotic stresses. In the future, PPO gene suppression in transgenic plants using anti-sense potato PPO gene construct can be used to inhibit enzymatic browning in fruits and vegetables, e.g., potato.