Mutations in the N-terminal coding region of the harpin protein Hpa1 from Xanthomonas oryzae cause loss of hypersensitive reaction induction in tobacco.
Harpins encoded by many gram-negative phytopathogenic bacterial hrp genes induce hypersensitive response (HR) and associated defense responses on nonhost plants. Hpa1(Xoo) and Hpa1(Xoc), two harpin proteins from Xanthomonas oryzae pathovars, induce HR when infiltrated into tobacco leaves. N- and C-terminal mutations of Hpa1(Xoo) and Hpa1(Xoc), respectively, were tested for their ability to elicit HR on tobacco. Deletion of codons for 12 highly hydrophilic amino acids (H(2)N-QGISEKQLDQLL-COOH) that partially overlap the N-terminal alpha-helical regions of respective proteins was found to be critical for the elicitation of HR in tobacco. Furthermore, two single missense mutants Hpa1(Xoo) (L51P) and Hpa1(Xoc) (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.
Wang
Xiao-yu
XY
Department of Plant Pathology, Nanjing Agricultural University, Weigang 1, Nanjing, 210095, China.
Song
Cong-feng
CF
Miao
Wei-guo
WG
Ji
Zhao-lin
ZL
Wang
Xiben
X
Zhang
Yan
Y
Zhang
Jia-huan
JH
Hu
John S
JS
Borth
Wayne
W
Wang
Jin-sheng
JS
D019943:Amino Acid Substitution / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D020869:Gene Expression Profiling; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000096:biosynthesis; D017354:Point Mutation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017384:Sequence Deletion; D014026:Nicotiana / Q000276:immunology / Q000382:microbiology*; D014027:Tobacco Mosaic Virus / Q000276:immunology; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*; D014974:Xanthomonas / Q000235:genetics / Q000472:pathogenicity*
D001425:Bacterial Outer Membrane Proteins; D010940:Plant Proteins; D037521:Virulence Factors; C075462:harpin protein, Erwinia amylovora