Expression profiling and functional analysis of poplar WRKY23 reveals a regulatory role in defense: WRKY23-RNAi

To investigate the function of poplar WRKY23, we generated PtWRKY23-overexpressing and -underexpressing (RNAi) plants. Transgenic plants were inoculated with Melampsora rust or mock-inoculated for assessment of rust-resistance and for gene expression profiling using the poplar Affymetrix GeneChip® to study the consequences of PtWRKY23 overexpression and underexpression. Transcriptome analysis of PtWRKY23 overexpressors revealed a significant overlap with the Melampsora-infection response. Transcriptome analysis also indicated that PtWRKY23 affects redox homeostasis and cell wall-related metabolism. Keywords: genetic modification, stress response Leaf discs from wildtype, WRKY23-overexpressor and WRKY23-RNAi plants were inoculated with Melampsora medusae f. sp. tremuloidae (Mmt) or were mock-inoculated (control). At five days post-inoculation, tissues were harvested for RNA extraction and hybridization on Affymetrix GeneChips®. Three biological replications were performed for each line and each inoculation or mock-inoculation. A total of 15 Affymetrix GeneChips® were used in this study. Data for the Mmt-inoculated WRKY23-RNAi plants were processed separately from the data for the WRKY23-overexpressor plants. The raw data for the Mmt-inoculated wildtype plants were the same in both cases. Normalized data for the Mmt-inoculated wildtype plants that were processed with the Mmt-inoculated WRKY23-RNAi plants are denoted with an "a" suffix. This part of the study includes 6 RNA samples consisting of three biological replicates for the Mmt-inoculated WT and WRKY23-RNAi (underexpressing) plants.