The Arabidopsis NIMIN cycle – shaping PR gene expression in the course of systemic acquired resistance

Abstract: Nonexpressor of Pathogenesis-Related Genes1 (NPR1) is a master regulator ofsystemic acquired resistance (SAR). NPR1 is part of a transcription complex mediating salicylicacid (SA)-induced expression of Pathogenesis-Related (PR) Protein1 genes through co-operationbetween different proteins. TGA transcription factors link NPR1 to the PR-1 promoter region,while NIMIN proteins control NPR1 activity. Based on gene expression analysis, protein-proteininteraction assays and functional in planta studies, we suggest that NIMIN3 suppresses PR geneexpression in unchallenged plants. NIMIN2 promotes transcription of early SA- and NPR1-dependent genes, whereas NIMIN1 becomes active only after NIMIN2 by blocking SA- andNPR1-dependent gene expression. The repressional block is relieved with increasing levels of SAto yield strong, sudden and coordinate expression of the late SAR-induced PR genes.