| Studies of pathogen defense systems in plants have been primarily focused on the aerial organs. In order to better cope with different pathogens, it appears likely that the pathogen defense responses in the shoots and the roots are specialized. However, a direct comparison between pathogen defense systems of roots and shoots has hardly been explored. Traditional methods of studying pathogen infection are not suitable for the root/shoot defense comparisons. To facilitate the study of defense signaling pathways, a simple Arabidopsis thaliana seedling assay was developed for pathogen defense studies. Although not without limitations, the seedling assay offers a number of benefits over traditional assays. Transcriptional profiling analysis of Arabidopsis seedlings treated with the purified defense elicitor Flg22 or salicylic acid (SA) was performed to directly compare the defense systems in the roots and the shoots. This revealed that root and shoot responses to Flg22 or SA differ significantly. Roots are less responsive to Flg22 treatment, but more responsive to SA treatment than shoots. Several genes that are preferentially induced in roots were identified. Furthermore, several WRKY transcription factors and so-called pathogenesis-related (PR) genes, which are known to be involved in pathogen defense, were shown to have different expression patterns in roots and shoots using reverse transcription-polymerase chain reaction (RT-PCR). Further investigation of genes that are differentially regulated by Flg22 and SA in roots and shoots and the cis-acting elements that regulate their expression should provide critical insights in the poorly understood field of root defense against pathogen attack. |
