Poster: Plant Pathogen/Symbiont Interactions
Abs #
737: The Involvement of Tobacco NtRac3 Gene in Regulation of Salicylic Acid mediated Signal Transduction
A small GTP binding protein, Rac, is thought to regulate organization of actin cytoskeleton and assembly of NADPH oxydase complex in mammalian cells. In plant genome, there are numbers of Rac genes are present and the products of the genes are thought to play diverse roles. Although the importance of Rac protein has been expected in higher plants, functions of the protein remains unclear. In this study, to investigate functions of tobacco Rac proteins in defense responses of plants, we made transgenic tobacco plants which overexpressed tobacco NtRac3 gene(OE-NtRac3). OE-NtRac3 was inoculated with bacterial pathogen, Pseudomonas syringae pv tabaci, acdic PR1 gene, which is a well-known marker of the systemic acquired resistance (SAR) induction, was rapidly induced, and the bacterial growth and lesion formation were markedly suppressed. Also, when lower leaves of OE-NtRac3 were inoculated with the pathogen, PR1 gene expression in upper leaves was significantly increased, comparing with wild-type plants. These results indicate that SAR response was enhanced in OE-NtRac3. Although regulation of reactive oxygen spices (ROS) generation is a putative role of Rac, no differences of H2O2 accumulation in infected leaves were observed between OE-NtRac3 and wild-type plants. On the other hand, PR1 gene expression was induced in OE-NtRac3 by lower dose of salicylic acid (SA), which never induced PR1 expression in wild-type plants. Thus, it appeared that enhanced SAR response in OE-NtRac3 was caused by the change of sensitivity to SA. These results strongly suggest that NtRac3 plays an important role in SA dependent defense pathway, independently of ROS regulation.
