Host-mediated phosphorylation of type III effector AvrPto promotes Pseudomonas virulence and avirulence in tomato.
The AvrPto protein from Pseudomonas syringae pv tomato is delivered into plant cells by the bacterial type III secretion system, where it either promotes host susceptibility or, in tomato plants expressing the Pto kinase, elicits disease resistance. Using two-dimensional gel electrophoresis, we obtained evidence that AvrPto is phosphorylated when expressed in plant leaves. In vitro phosphorylation of AvrPto by plant extracts occurs independently of Pto and is due to a kinase activity that is conserved in tomato (Solanum lycopersicum), tobacco (Nicotiana tabacum), and Arabidopsis thaliana. Three Ser residues clustered in the C-terminal 18 amino acids of AvrPto were identified in vitro as putative phosphorylation sites, and one site at S149 was directly confirmed as an in vivo phosphorylation site by mass spectrometry. Substitution of Ala for S149 significantly decreased the ability of AvrPto to enhance disease symptoms and promote growth of P. s. tomato in susceptible tomato leaves. In addition, S149A significantly decreased the avirulence activity of AvrPto in resistant tomato plants. Our observations support a model in which AvrPto has evolved to mimic a substrate of a highly conserved plant kinase to enhance its virulence activity. Furthermore, residues of AvrPto that promote virulence are also monitored by plant defenses.
Anderson
Jeffrey C
JC
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA.
Pascuzzi
Pete E
PE
Xiao
Fangming
F
Sessa
Guido
G
Martin
Gregory B
GB
D000409:Alanine / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005998:Glycine / Q000378:metabolism; D006790:Host-Parasite Interactions; D007113:Immunity, Innate; D018551:Solanum lycopersicum / Q000378:metabolism* / Q000821:virology*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D010935:Plant Diseases; D010940:Plant Proteins / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D012694:Serine / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D014026:Nicotiana / Q000033:anatomy & histology / Q000166:cytology / Q000821:virology; D014774:Virulence
D001426:Bacterial Proteins; D010940:Plant Proteins; C081695:avrPto protein, Pseudomonas syringae; D012694:Serine; D010770:Phosphotransferases; D000409:Alanine; D005998:Glycine