PMC

Nucleo-cytoplasmic trafficking of TFs and regulators during plant defense responses. A, The secreted phospholipase AtsPLA₂-α is partially relocalized from Golgi-associated vesicles to the nucleus, where it interacts with the positive defense and HR regulator AtMYB30. This nuclear protein interaction leads to down-regulation of AtMYB30 transcriptional activation of VLCFA-related genes and, therefore, suppression of HR and defense responses. B, Pathogen-induced SA and reactive oxygen species (ROS) production leads to a change in the oligomerization state of the transcriptional coactivator NPR1, which is translocated into the nucleus in its monomeric active form. In the nucleus, active NPR1 interacts with TGA TFs and enhance their DNA-binding properties during the establishment of SAR. NPR1 nuclear accumulation is regulated by the proteasome.

Nuclear translocation of bacterial effectors and plant resistance proteins. A, After dimerizing in the plant cell cytoplasm, AvrBs3 is translocated into the nucleus, where it is able to bind to the UPA box and act as a TF. Transcriptional activation of UPA20 induces plant cell hypertrophy, whereas in resistant pepper, activation of the R gene Bs3 leads to HR. B, XopD nuclear interaction with the Arabidopsis TF AtMYB30 is mediated by the HLH domain of XopD, which is necessary and sufficient to repress AtMYB30 transcriptional activation and thereby the plant defense response. C, In resting cells, the N immune receptor presents a dual cytoplasmic and nuclear localization. Upon TMV infection, the viral replicase p50 recruits to the cytoplasm the tobacco NRIP1 protein, which is localized in the chloroplast of uninfected cells. The NRIP1/p50 prerecognition complex interacts with and activates cytoplasmic N, which is then able to cross the nuclear envelope and/or send a signal to activate nuclear N, thereby activating defense signaling. D, The PopP2 effector induces nuclear accumulation of its cognate R protein RRS1-R, which acts as a transcriptional repressor in resting cells, and of the vacuolar protease RD19. The nuclear interaction between the PopP2/RD19 complex and RRS1-R leads to activation of plant defense, perhaps through modification of the transcriptional activity of RRS1-R WRKY domain or by activation of additional TFs. It has been additionally proposed that PopP2 acetyltransferase activity may disrupt higher-order packaging of the chromatin or alter DNA-binding activities and interaction properties of host TFs, leading to modification of their activity.