Molecular sensing of bacteria in plants. The highly conserved RNA-binding motif RNP-1 of bacterial cold shock proteins is recognized as an elicitor signal in tobacco.
To detect microbial infection multicellular organisms have evolved sensing systems for pathogen-associated molecular patterns (PAMPs). Here, we identify bacterial cold shock protein (CSP) as a new such PAMP that acts as a highly active elicitor of defense responses in tobacco. Tobacco cells perceive a conserved domain of CSP and synthetic peptides representing 15 amino acids of this domain-induced responses at subnanomolar concentrations. Central to the elicitor-active domain is the RNP-1 motif KGFGFITP, a motif conserved also in many RNA- and DNA-binding proteins of eukaryotes. Csp15-Nsyl, a peptide representing the domain with highest homology to csp15 in a protein of Nicotiana sylvestris exhibited only weak activity in tobacco cells. Crystallographic and genetic data from the literature show that the RNP-1 domain of bacterial CSPs resides on a protruding loop and exposes a series of aromatic and basic side chains to the surface that are essential for the nucleotide-binding activity of CSPs. Similarly, these side chains were also essential for elicitor activity and replacement of single residues in csp15 with Ala strongly reduced or abolished activity. Most strikingly, csp15-Ala10, a peptide with the RNP-1 motif modified to KGAGFITP, lacked elicitor activity but acted as a competitive antagonist for CSP-related elicitors. Bacteria commonly have a small family of CSP-like proteins including both cold-inducible and noninducible members, and Csp-related elicitor activity was detected in extracts from all bacteria tested. Thus, the CSP domain containing the RNP-1 motif provides a structure characteristic for bacteria in general, and tobacco plants have evolved a highly sensitive chemoperception system to detect this bacterial PAMP.
Felix
Georg
G
Friedrich Miescher-Institute, P. O. Box 2543, CH-4002 Basel, Switzerland. Felix@fmi.ch
Boller
Thomas
T
D016960:Agrobacterium tumefaciens / Q000472:pathogenicity / Q000502:physiology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010935:Plant Diseases / Q000382:microbiology; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000472:pathogenicity / Q000502:physiology; D014026:Nicotiana / Q000382:microbiology* / Q000502:physiology; D016959:Xanthomonas campestris / Q000472:pathogenicity / Q000502:physiology
D001426:Bacterial Proteins; D010446:Peptide Fragments; D016601:RNA-Binding Proteins