Colorized scanning electron micrograph image of the foliar bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) on the leaf surface of Arabidopsis thaliana. In order to cause disease, Pst DC3000 must gain entry to the empty space within the leaf (apoplastic space) via stomata (gas exchange pores) or other openings (image by James M. Kremer, Michigan State University, USA, currently at AgBiome, Research Triangle Park, USA; and Carol Flegler, Michigan State University, USA); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.