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Constitutive Expression of hrap Gene in Transgenic Tobacco Plant Enhances Resistance Against Virulent Bacterial Pathogens by Induction of a Hypersensitive Response

August 2002 , Volume 15 , Number  8
Pages  764 - 773

Mang-jye Ger , 1 Cheng-hsien Chen , 2 Shaw-yhi Hwang , 2 Hsiang-en Huang , 3 Appa Rao Podile , 2 , 4 Badri Venkata Dayakar , 2 and Teng-yung Feng 1 , 2

1Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan, Republic of China; 2Institute of Botany, Academia Sinica, Taipei, 115, Taiwan, Republic of China; 3Institute of Pathology, National Taiwan University, Taipei, 115, Taiwan, Republic of China; 4Department of Plant Science, University of Hyderabad, Hyderabad-500 046, India

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Accepted 8 April 2002.

Hypersensitive response-assisting protein (HRAP) has been previously reported as an amphipathic plant protein isolated from sweet pepper that intensifies the harpinPss-mediated hypersensitive response (HR). The hrap gene has no appreciable similarity to any other known sequences, and its activity can be rapidly induced by incompatible pathogen infection. To assess the function of the hrap gene in plant disease resistance, the CaMV 35S promoter was used to express sweet pepper hrap in transgenic tobacco. Compared with wild-type tobacco, transgenic tobacco plants exhibit more sensitivity to harpinPss and show resistance to virulent pathogens (Pseudomonas syringae pv. tabaci and Erwinia carotovora subsp. carotovora). This disease resistance of transgenic tobacco does not originate from a constitutive HR, because endogenous level of salicylic acid and hsr203J mRNA showed similarities in transgenic and wild-type tobacco under noninfected conditions. However, following a virulent pathogen infection in hrap transgenic tobacco, hsr203J was rapidly induced and a micro-HR necrosis was visualized by trypan blue staining in the infiltration area. Consequently, we suggest that the disease resistance of transgenic plants may result from the induction of a HR by a virulent pathogen infection.

© 2002 The American Phytopathological Society