An importin-α IMA8 facilitates nuclear import of COI1 to promote jasmonate-mediated defense responses in Arabidopsis.

Jasmonate (JA) is an essential phytohormone that coordinates plant defense, growth, and developmental processes in response to diverse environmental cues. The JA receptor CORONATINE INSENSITIVE 1 (COI1) is a core component of JA signaling and functions in the nucleus to regulate JA-responsive transcription. However, how newly synthesized COI1 in the cytoplasm is imported into the nucleus remains unclear. Here, we identified an importin IMPORTIN ALPHA ISOFORM 8 (IMA8) as a nuclear transport receptor (NTR) for COI1. We found that IMA8 positively regulates JA responses. Biochemical analyses confirmed an interaction between IMA8 and COI1. Both in vitro transport assay and in vivo nucleo-cytoplasmic fractionation experiment demonstrated that IMA8 facilitates the nuclear import of COI1. Furthermore, the hypersensitive phenotypes triggered by COI1 overexpression were markedly suppressed in the ima8 mutant, indicating that COI1 function depends on IMA8-facilitated nuclear import. Together, our results reveal a previously unrecognized regulatory step in JA signaling, and provide new insights into the spatial organization of plant defense pathways.