Rd. Frederick et al., RECOGNITION SPECIFICITY FOR THE BACTERIAL AVIRULENCE PROTEIN AVRPTO IS DETERMINED BY THR-204 IN THE ACTIVATION LOOP OF THE TOMATO PTO KINASE, MOLECULAR CELL, 2(2), 1998, pp. 241-245
The Pto kinase confers resistance in tomato to P. syringae pv. tomato
strains expressing the AvrPto protein. Physical interaction of the Pto
kinase and AvrPto protein in the plant cell initiates host defense re
sponses. The recognition event between these two proteins is very spec
ific; AvrPto does not interact with other closely related kinases, inc
luding the Fen kinase, which shares 80% amino acid identity with Pto.
By using Pto-Fen chimeric proteins and site-directed mutagenesis, we f
ound that Thr-204 is required for Pto interaction with AvrPto in a yea
st two-hybrid system and for recognition specificity in a tobacco leaf
transient assay. Substitution of Thr-204 into the Fen kinase allowed
that kinase to interact with AvrPto and to confer an AvrPto-specific d
efense response in tobacco leaves. Thus, simple mutations appear capab
le of giving rise to new resistance gene specificities.