First published online February 27, 2003; 10.1104/pp.016113
Plant Physiol, March 2003, Vol. 131, pp. 1239-1249
Pto Mutants Differentially Activate
Prf-Dependent, avrPto-Independent Resistance
and Gene-for- Gene Resistance1
Fangming
Xiao,
Ming
Lu,
Jianxiong
Li,
Tiehan
Zhao,
Seung Young
Yi,
Venkatappa K.
Thara,
Xiaoyan
Tang, and
Jian-Min
Zhou*
Department of Plant Pathology, Kansas State University, Manhattan,
Kansas 66506
Pto confers disease resistance to
Pseudomonas syringae pv tomato carrying
the cognate avrPto gene. Overexpression of
Pto under the cauliflower mosaic virus 35S promoter
activates spontaneous lesions and confers disease resistance in tomato
(Lycopersicon esculentum) plants in the absence of
avrPto. Here, we show that these AvrPto-independent
defenses require a functional Prf gene. Several
Pto-interacting (Pti) proteins are thought to play a role in
Pto-mediated defense pathways. To test if interactions with Pti
proteins are required for the AvrPto-independent defense responses by
Pto overexpression, we isolated several Pto mutants that were unable to
interact with one or more Pti proteins, but retained normal interaction
with AvrPto. Overexpression of two mutants, PtoG50S and
PtoR150S, failed to activate
AvrPto-independent defense responses or confer enhanced resistance to
the virulent P. s. pv tomato. When
introduced into plants carrying 35S::Pto,
35S::PtoG50S
dominantly suppressed the AvrPto-independent resistance caused by
former transgene. 35S::PtoG50S also
blocked the induction of a number of defense genes by the wild-type
35S::Pto. However,
35S::PtoG50S and
35S::PtoR150S plants were completely
resistant to P. s. pv tomato (avrPto), indicating a normal gene-for-gene resistance. Furthermore,
35S::PtoG50S plants exhibited normal
induction of defense genes in recognition of avrPto.
Thus, the AvrPto-independent defense activation and gene-for-gene
resistance mediated by Pto are functionally separable.
1
This work was supported by the National Science
Foundation (grant no. MCB9808701 to J.-M.Z.) and by the U.S. Department
of Agriculture (grant no. 9802511 to X.Y.T.). This is Kansas
Agricultural Experimental Station contribution no. 02-170-A.
*
Corresponding author; e-mail jzhou{at}ksu.edu; fax
785-532- 5692.
© 2003 American Society of Plant Biologists
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