Biotic stress-response gene expression. A total of 228 genes significantly regulated in response to Pseudomonas syringaeDC3000 (avrRpt2), P. syringae DC3000 (vector control), Xanthomonas campestris, and buffer control were grouped using k-means clustering (k = 6; Euclidean distance). Predicted role categories are denoted by color-coded squares; genes also found to be significantly regulated in response to abiotic stresses are denoted with blue circles.