A major component of plant disease resistance against pathogens is inducible defense: A plant recognizes pathogen attack and activates a wide variety of defense mechanisms. My group is studying the recognition and signal transduction events controlling this process. Since the resistance mechanism appears to be well conserved among higher plants responding to a wide variety of pathogens, we use a model plant-pathogen system composed of Arabidopsis thaliana as the plant host and Pseudomonas syringae as the bacterial pathogen. The heart of the signal transduction mechanism is a complex signaling network. In order to elucidate the network structure and dynamics, it is essential to introduce various perturbations and measure the consequences at many points within the network. We use mutations to create perturbations and expression profiling as a primary measurement method. We have collected plant lines with mutations in more than 100 genes. We have developed a microarray method for accurate and inexpensive expression profiling. Based on my experience serving in a study panel for international research and development on systems biology (http://wtec.org/sysbio/welcome.htm), I would also like to discuss desirable changes in styles of collaboration between experimentalists and theoreticians/computer scientists to promote efficient systems biology research.