Nuclear trafficking during plant innate immunity.

Land plants possess innate immune systems that can control resistance against pathogen infection. Conceptually, there are two branches of the plant innate immune system. One branch recognizes conserved features of microbial pathogens, while a second branch specifically detects the presence of pathogen effector proteins by plant resistance (R) genes. Innate immunity controlled by plant R genes is called effector-triggered immunity. Although R genes can recognize all classes of plant pathogens, the majority can be grouped into one large family, encoding proteins with a nucleotide binding site and C-terminal leucine rich repeat domains. Despite the importance and number of R genes present in plants, we are just beginning to decipher the signaling events required to initiate defense responses. Recent exciting discoveries have implicated dynamic nuclear trafficking of plant R proteins to achieve effector-triggered immunity. Furthermore, there are several additional lines of evidence implicating nucleo-cyctoplasmic trafficking in plant disease resistance, as mutations in nucleoporins and importins can compromise resistance signaling. Taken together, these data illustrate the importance of nuclear trafficking in the manifestation of disease resistance mediated by R genes.