NIMIN-1, NIMIN-2 and NIMIN-3, members of a novel family of proteins from Arabidopsis that interact with NPR1/NIM1, a key regulator of systemic acquired resistance in plants

NPR1/NIM1 is a key regulator of systemic acquired resistance (SAR) in Arabidopsis. Using the yeast two-hybrid system, we have identified three novel genes, NIMIN-1, NIMIN-2 and NIMIN-3 (NIMIN for NIM1-interacting) that encode structurally related proteins interacting physically with NPR1/NIM1. NIMIN-1 and NIMIN-2 both bind strongly to NPR1/NIM1 via a common binding motif interacting with the C-terminal moiety of NPR1/NIM1, whereas NIMIN-3 interacts with NPR1/NIM1 via the N-terminal part of NPR1/NIM1. In addition, NIMIN-1, NIMIN-2, and NIMIN-3 are able to interact via NPR1/NIM1 with basic leucine zipper transcription factors of the TGA family in a yeast tri-hybrid system. A mutant protein of NPR1/NIM1, npr1-2, which has been shown to be severely impaired in induction of SAR gene expression, failed to bind the NIMIN proteins. The NIMIN genes are expressed in Arabidopsis plants in response to SAR-inducing treatments, and the NIMIN proteins, like NPR1/NIM1, carry functional nuclear localization signals as revealed by expression of fusion proteins in yeast and in transgenic plants. Taken together, these data indicate that the NIMIN proteins, via physical interaction with NPR1/NIM1, are part of the signal transduction pathway leading to SAR gene expression in Arabidopsis.