Functional analyses of the Pto resistance gene family in tomato and the identification of a minor resistance determinant in a susceptible haplotype.
Pto is a member of a multigene family and encodes a serine/threonine kinase that mediates gene-for-gene resistance to strains of Pseudomonas syringae pv. tomato expressing avrPto. The inferred amino acid sequence of the Pto homologs from both resistant (LpimPth2 to LpimPth4) and susceptible (LescFen, LescPth2 to LescPth5) haplotypes suggested that most could encode functional serine/threonine kinases. In addition, the activation segments of the homologs are similar in sequence to that of Pto, and some have residues previously identified as required for binding of AvrPto by Pto in the yeast two-hybrid system. The Pto homologs were therefore characterized for transcription, for the ability of their products to interact with AvrPto in the yeast two-hybrid system, for their autophosphorylation activity, and for their potential to elicit cell death in the presence of and absence of a ligand, as well as their dependence on Prf. LpimPth5, LpimPth4, and LescPth4 were not transcribed at levels detectable by reverse transcription-polymerase chain reaction. The interaction with AvrPto was unique to Pto in the yeast two-hybrid system. LescPth2 autophosphorylated in vitro as a fusion protein. LpimPth2, LpimPth3, LpimPth4, LescPth3, and LescPth4 did not autophosphorylate in vitro. Transient expression of wild-type Fen and wild-type LpimPth3, as well as LescFen, LescPth3, and LescPth5 with perturbations in their P+1 loop caused cell death in Nicotiana benthamiana. LpimPth3 and LescPth3 with amino acid substitutions in the P+1 loop also elicited cell death in tomato; this was dependent on the presence of wild-type Prf. Consequently, some homologs could potentially encode functional resistance proteins. LescPth5 induced cell death specifically in response to expression of AvrPto in tobacco in a Prf-dependent manner; this is consistent with a homolog from a 'susceptible' haplotype encoding a minor recognition determinant.
Chang
Jeff H
JH
NSF Center for Engineering Plants for Resistance Against Pathogens, University of California, Davis, 95616 USA.
Tai
Yin-Shan
YS
Bernal
Adriana J
AJ
Lavelle
Daniel T
DT
Staskawicz
Brian J
BJ
Michelmore
Richard W
RW
D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D017343:Genes, Plant; D020022:Genetic Predisposition to Disease; D006239:Haplotypes; D007113:Immunity, Innate / Q000235:genetics; D018551:Solanum lycopersicum / Q000235:genetics* / Q000382:microbiology*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011549:Pseudomonas / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D010940:Plant Proteins; C084354:Pto protein, Lycopersicon; D017346:Protein Serine-Threonine Kinases