Mutations in the N-terminal coding region of the harpin protein Hpa1 from Xanthomonas oryzae cause loss of hypersensitive reaction induction in tobacco

• Published in: Applied microbiology and biotechnology 2008-11, Vol.81 (2), p.359-369
• Main Authors: Wang, Xiao-yu, Song, Cong-feng, Miao, Wei-guo, Ji, Zhao-lin, Wang, Xiben, Zhang, Yan, Zhang, Jia-huan, Hu, John S, Borth, Wayne, Wang, Jin-sheng
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution - genetics; Amino acids; Apoptosis; Applied Microbial and Cell Physiology; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Binding sites; Biotechnology; Cell death; Cellular biology; Cloning; Dimerization; E coli; Gene Expression Profiling; Genes; Hpa1; hypersensitive response; Hypersensitivity; induced resistance; Life Sciences; Microbial Genetics and Genomics; Microbiology; Mutagenesis; Mutation; N-terminal α-helix; Nicotiana - immunology; Nicotiana - microbiology; Pathogenesis; Pathogens; Plant Diseases - microbiology; Plant Proteins - biosynthesis; Plant resistance; Plasmids; Point Mutation; Protein Binding; Protein Interaction Domains and Motifs; Proteins; Sequence Deletion; Studies; Tobacco; Tobacco Mosaic Virus - immunology; Virulence Factors - genetics; Virulence Factors - metabolism; Xanthomonas - genetics; Xanthomonas - pathogenicity; Xanthomonas oryzae
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-008-1651-7

Harpins encoded by many gram-negative phytopathogenic bacterial hrp genes induce hypersensitive response (HR) and associated defense responses on nonhost plants. Hpa1Xoo and Hpa1Xoc, two harpin proteins from Xanthomonas oryzae pathovars, induce HR when infiltrated into tobacco leaves. N- and C-terminal mutations of Hpa1Xoo and Hpa1Xoc, respectively, were tested for their ability to elicit HR on tobacco. Deletion of codons for 12 highly hydrophilic amino acids (H₂N-QGISEKQLDQLL-COOH) that partially overlap the N-terminal α-helical regions of respective proteins was found to be critical for the elicitation of HR in tobacco. Furthermore, two single missense mutants Hpa1Xoo (L51P) and Hpa1Xoc (L53P) that are predicted to destroy the coiled-coil integrity and inhibit the dimer formation eliminated HR elicitation activity in tobacco. However, both wild-type proteins and derivative mutants retained the ability to induce systemic acquired resistance in tobacco against tobacco mosaic virus. Accumulations of npr1 (nonexpressor of pathogenesis-related protein 1), hsr515 (hypersensitivity-related protein 515), and pr2 (pathogenesis-related protein 2) transcripts were found in tobacco plants infiltrated with wild-type or mutated proteins.