Update on Nuclear Dynamics in Plant Immune Responses Nuclear Dynamics during Plant Innate Immunity

Plants are sessile organisms living in an environment rich in microbes that are potentially able to cause disease. As a result, plant survival depends on the ability to couple rapid pathogen detection to an efficient defense response. In contrast to the somatic adaptive immune system of mammals involving mobile defender cells, plant immune responses rely on the ability of each cell to recognize and respond to pathogen invasion and on systemic signals originating from infection sites. A first line of plant defense is activated after recognition of pathogenor microbeassociated molecular patterns (PAMPs or MAMPs), which are highly conserved among microbes. PAMP recognition by specific pattern recognition receptors leads to PAMP-triggered immunity (PTI), which induces basal defenses thereby preventing further pathogen ingress (Jones and Dangl, 2006). To counteract PTI, thriving pathogens gained the ability to secrete virulence effectors able to target crucial PTI regulators. In turn, plants evolved to produce resistance (R) proteins that recognize pathogen-produced effectors or their action on host components, leading to effector-triggered immunity (ETI). ETI provides a second layer of plant defense that is frequently associated to the development of a form of programmed cell death, the so-called hypersensitive response (HR; Jones and Dangl, 2006). Plant immunity against microbial infection engages highly dynamic responses that involve multiple organelles during the recognition and signaling mechanisms associated to defense. A particularly important role in plant defense responses has been attributed to nuclear dynamics, since a growing number of reports revealed that nuclear localization of pathogen effectors, R proteins, and key host components, including transcription factors (TFs) and regulators, is essential for plant immunity (Deslandes and Rivas, 2011). Spatial restriction of defense regulators by the nuclear envelope as well as their stimulus-induced nuclear translocation provide an important mechanism for defense regulation, as their level of nuclear accumulation determines the output of the defense response. Interestingly, mutations in cellular factors involved in the transport of macromolecules through the nuclear envelope, compromise plant resistance signaling, underlining the importance of nucleocytoplasmic trafficking during plant innate immunity (Deslandes and Rivas, 2011). Together, these findings situate the nucleus at the forefront of themutual recognition between plants and pathogens. Here, I provide a summary of our current knowledge about nuclear dynamics during plant immune responses.