Plants possess innate immune systems to prevent most potential infections. The ancient and conserved innate immune responses are triggered by microbe-associated molecular patterns (MAMPs) and play important roles in broad-spectrum defenses. However, successful bacterial pathogens evolved type III virulence effectors to suppress MAMP-mediated immunity. To survive, plants further developed highly specific resistance (R) genes to trigger gene-for-gene-mediated immunity and turn the virulent pathogens into avirulent ones. We summarize here the very recent advances in this dynamic coevolution of plant-bacterium interaction.Author for correspondence. Tel: +1 617 643 3314; E-mail: shan@molbio.mgh.harvard.edu