OsWRKY62 and OsWRKY76 interact with Importin α1s for Negative Regulation of Defensive Responses in Nucleus
Background: OsWRKY62 and OsWRKY76, two close members of WRKY transcription factors, function together as transcriptional repressors. OsWRKY62 is predominantly localized in the cytosol. What are the regulatory factors for OsWRKY62 nuclear translocation?Results: In this study, we characterized they interacted with rice importin, OsIMα1a and OsIMα1b, for nuclear translocation. Chimeric OsWRKY62.1-GFP, which is predominantly localized in the cytoplasm, was translocated to the nucleus of Nicotiana
... nthamiana leaf cells in the presence of OsIMα1a or OsIMαDIBB1a lacking the auto-inhibitory importin β-binding domain. OsIMαDIBB1a interacted with the WRKY domain of OsWRKY62.1, which has specific bipartite positively charged concatenated amino acids functioning as a nuclear localization signal. Similarly, we found that OsIMαDIBB1a interacted with the AvrPib effector of rice blast fungus Magnaporthe oryzae, which contains a scattered distribution of positively charged amino acids. Furthermore, we identified a nuclear export signal in OsWRKY62.1 that inhibited nuclear transportation. Overexpression of OsIMα1a or OsIMα1b enhanced resistance to M. oryzae, whereas knockout mutants decreased resistance to the pathogen. However, overexpressing both OsIMα1a and OsWRKY62.1 were slightly more susceptible to M. oryzae than OsWRKY62.1 alone. Ectopic overexpression of OsWRKY62.1 with an extra nuclear export signal compromised the enhanced susceptibility of OsWRKY62.1 to M. oryzae.Conclusion: These results indicated that OsWRKY62 localization is a consequence of competition binding between rice importins and exportins. OsWRKY62, OsWRKY76, and AvrPib effector translocate to nucleus in association with importin α1s through new types of nuclear localization signals for negatively regulating defense responses.