The Nucleoporin CPR5 Modulates Plant Immunity via Guanylate-Binding Proteins.

The nuclear pore complex plays a key role in nuclear transport of immune signals. Two nucleoporins, CONSTITUTIVE EXPRESSION OF PR GENES 5 (CPR5) and GUANYLATE-BINDING PROTEIN-LIKE 3 (GBPL3), have been implicated in plant immunity. The Arabidopsis GBPL family comprises three members. While GBPL1 and GBPL3 were discovered to form an immune circuit, the role of GBPL2 remains unknown. Through genetic screening, we identified a gain-of-function mutation in GBPL2, named suppressor of cpr5 23 (scpr23), that fully suppresses the cpr5 mutant phenotype. The scpr23 function is attributed to a core amino acid residue within a nuclear export signal (NES) motif; its alteration causes a change of GBPL2 localisation from the endoplasmic reticulum to the nuclear envelope. Epistatic analysis demonstrated that knockdown of GBPL3 expression in the cpr5 scpr23 double mutant reverted its phenotype to that of the cpr5 mutant, indicating that the function conferred by scpr23 is mediated by GBPL3. We further found that GBPL2 is a counterpart of mammalian ATLASTIN-1, which belongs to a subfamily of the GBP proteins featuring transmembrane domains. Therefore, our findings reveal that the GBPL family proteins form a signalling complex that functions downstream of CPR5 to modulate plant immunity.