Pathogen Recognition and Immune Signaling

Rice blast and bacterial blight, two important rice diseases, are caused by infection with a fungal pathogen Magnaporthe oryzae and a bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo), respectively. Recent studies on the interaction between rice and these pathogens provided important knowledges of the molecular mechanisms of rice immune responses such as receptor-mediated pathogen recognition, host immune signaling, and pathogen effector-mediated susceptibility. So far, many disease resistance (R) genes have been genetically identified based upon disease resistance traits against M. oryzae and Xoo. Most rice blast R genes isolated to date encode pathogen recognition receptors. In contrast, the majority of bacterial blight R genes are involved in transcriptional regulation of host resistance or susceptibility factors. Genetic and biochemical studies of rice immune signaling have identified important immune factors including OsRac1, OsRLCK185, and WRKY45. Identification of rice factors that interact with OsRac1, OsRLCK185, and WRKY45 revealed the molecular mechanisms of a variety of immune responses, including the expression of defense-related genes, production of reactive oxygen species (ROS), activation of mitogen-activated protein kinase (MAPK), and lignification.