The Arabidopsis NPR1 protein is a key regulator of salicylic acid
The Arabidopsis NPR1 protein is a key regulator of salicylic acid (SA)-mediated gene expression in systemic acquired resistance. phenotypes much like those of mutants. This dominant-negative effect of the TGA2 mutant demonstrates TGA2 and NPR1 interact in planta. We also present biochemical evidence indicating that this connection is definitely specific and enhanced by SA treatment. Moreover using a chimera reporter system we found that a chimeric TGA2GAL4 transcription element triggered a reporter gene Mouse monoclonal to OVA in response to SA and that this activation was abolished in the mutant. NPR1 is required for the DNA binding activity of the transcription element. These genetic data clearly demonstrate that TGA2 is definitely a SA-responsive and NPR1-dependent transcription activator. INTRODUCTION Systemic acquired resistance (SAR) is definitely AC220 a plant defense response induced after a local hypersensitive response to avirulent pathogens or by treatment with transmission molecules such as salicylic acid (SA) 2 6 acid (INA) and benzothiadiazole (Ryals et al. 1996 Induction of SAR entails the activation of many pathogenesis-related ((nonexpresser of genes) mutants (also known as and gene induction and disease resistance under SAR-activating conditions. The positive part of NPR1 in SAR suggested from the phenotype of these recessive mutants was further shown by overexpression experiments. Overexpression of the gene in Arabidopsis and rice rendered the transgenic vegetation more resistant to numerous pathogens in the absence of a SAR inducer or after treatment with lower-than-normal concentrations of the inducer (Cao et al. 1998 Chern et al. 2001 Friedrich et AC220 al. 2001 Interestingly overexpression of did not result in constitutive gene manifestation before pathogen challenge indicating that the NPR1 protein requires activation maybe by SA to be practical in gene activation. The derived amino acid sequence of the NPR1 protein (Cao et al. 1997 Ryals et al. 1997 offers provided some suggestions about its molecular function. A AC220 bipartite nuclear localization sequence in the carboxyl end of NPR1 mediates its nuclear localization which is required for the induction of genes (Kinkema et al. 2000 NPR1 also contains two protein-protein connection domains: a BTB/POZ website (Aravind and Koonin 1999 in the N-terminal end and an ankyrin-repeat website (ARD) in the center of the protein (Cao et al. 1997 Although many proteins consist of either BTB/POZ or ARD domains NPR1 belongs to a unique family of proteins that carry both domains. The practical importance of these protein-protein connection domains is definitely highlighted by the various mutants recognized with amino acid changes in the consensus of these domains (Cao et al. 1997 Ryals et al. 1997 The presence of two protein-protein connection domains but the lack of a DNA binding website suggest that NPR1 may exert its regulatory part in gene manifestation through connection with transcription factors. Indeed using candida two-hybrid screens we while others found that NPR1 interacts with the TGA subclass of fundamental AC220 Leu zipper (bZIP) transcription factors (Zhang et al. 1999 Després et al. 2000 Niggeweg et al. 2000 Zhou et al. 2000 Chern et al. 2001 suggesting that TGA factors could be the missing link between NPR1 and its target genes. This notion is supported by several studies in which the binding sites for TGA transcription factors AC220 (e.g. the element) in gene promoters were found to be responsible for SA-mediated gene induction (Qin et al. 1994 Shah and Klessig 1996 Lebel et al. 1998 Even though seven known Arabidopsis TGA transcription factors have high examples of amino acid sequence identity and similarity they have different affinities toward NPR1 in the candida two-hybrid assay with TGA2 (1st known as AHBP-1b) TGA3 and TGA6 showing the strongest binding (Zhang et al. 1999 Després et al. 2000 Niggeweg et al. 2000 Zhou et al. 2000 The TGA factors also differ in their binding affinity and specificity to the element (Miao et al. 1994 Lam and Lam 1995 Xiang et al. 1997 These results suggest that some TGA factors may have redundant or overlapping functions whereas others may perform different tasks in regulating genes in flower defense and additional biological processes. Moreover TGA factors can form homodimers and heterodimers through their highly conserved bZIP domains further enhancing the versatility of these transcription factors (Foster et al. 1994 Lam and Lam 1995 However these characteristics make it.