NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 (NPR1) and some NPR1-related proteins are sensitive to salicylic acid.
NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 (NPR1; also known as NIM1) is a master regulator of systemic acquired resistance (SAR). SAR is induced by salicylic acid (SA), leading to the expression of PATHOGENESIS-RELATED (PR) genes. Current evidence suggests that NPR1 is part of a transcription complex tethered to activation sequence-1 (as-1)-like cis-acting elements in PR-1 gene promoters through TGA transcription factors, and that SA-dependent PR-1 gene expression is regulated by NIM1-INTERACTING (NIMIN) proteins. In Arabidopsis, NPR1 is active only after SA induction. Regulation of Arabidopsis NPR1 activity has been proposed to comprise cysteine-156 (Cys-156), mediating SA-induced cytoplasmic oligomer-nuclear monomer exchange, and Cys-521 and Cys-529, mediating SA-dependent transcriptional activation. Tobacco NPR1 does not harbour these residues. To understand the function of tobacco NPR1, we analysed its biochemical capabilities in a heterologous system: yeast. Tobacco NPR1 differs from Arabidopsis NPR1 in its subcellular localization and its transactivation potential. Yet, both tobacco and Arabidopsis NPR1, as well as tobacco NIM1-like1, alter some of their biochemical activities in response to SA. Whereas the addition of SA to yeast growth medium induces transcriptional activity in tobacco NPR1, its interaction with NIMIN2-type proteins is suppressed. The effects of SA are specific, sensitive and occur coordinately. They are abolished completely by mutation of the arginine residue within the invariable penta-amino acid motif LENRV, as present in the nonfunctional Arabidopsis nim1-4 allele. Furthermore, NPR1 proteins with the LENRV domain coincidently harbour a broad and strongly conserved NIMIN1/NIMIN2 binding site. Our data suggest that NPR1 and some NPR1-like proteins are sensitive to the plant hormone SA, altering some of their biochemical capabilities to enable stimulus-dependent gene expression. The sensitivity of NPR1 proteins to SA, together with their differential interaction with diverse NIMIN proteins, seems a plausible molecular basis for the timely and coordinated activation of PR genes during SAR.
Institut für Genetik, Universität Hohenheim, FG Allgemeine Virologie, D-70593 Stuttgart, Germany.
Felix
F
Maier
Sylvia
S
Zwicker
Angela
A
Hückelhoven
Meike
M
Meissner
Jennifer
J
Funk
Artur J P
AJ
Pfitzner
Ursula M
UM
Pfitzner
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D020156:Salicylic Acid / Q000494:pharmacology*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013045:Species Specificity; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; C105496:NPR1 protein, Arabidopsis; D010940:Plant Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D020156:Salicylic Acid