THE PLANT CELL, Vol 5, Issue 1 57-63, Copyright © 1993 by American Society of Plant Biologists
Suppression of Bean Defense Responses by Pseudomonas syringae
J. L. Jakobek, J. A. Smith and P. B. Lindgren
Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina 27695-7616
We have developed a model system to examine suppression of defense
responses in bean by the compatible bacterium Pseudomonas syringae pv
phaseolicola. Previously, we have shown that there is a general mechanism
for the induction of the bean defense genes phenylalanine ammonia-lyase
(PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and chitinase
(CHT) by incompatible, compatible, and nonpathogenic bacteria. Here, we
show that bean plants infiltrated with isolates of P. s. phaseolicola
failed to produce transcripts for PAL, CHS, or CHI up to 120 hr after
infiltration and CHT transcript accumulation was significantly delayed when
compared to the incompatible P. syringae strains. Infiltration of bean
plants with 108 cells per mL of P. s. phaseolicola NPS3121 8 hr prior to
infiltration with an equal concentration of incompatible P. s. pv tabaci
Pt11528 significantly reduced the typical profile of defense transcript
accumulation when compared to plants infiltrated with Pt11528 alone. A
corresponding suppression of phytoalexin accumulation was also observed.
NPS3121 also suppressed PAL, CHS, CHI, and CHT transcript accumulation and
phytoalexin production induced by Escherichia coli DH5[alpha] or the
elicitor glutathione. Heat-killed NPS3121 cells or cells treated with
protein synthesis inhibitors lost the suppressor activity. Taken together,
these experiments suggest that NPS3121 has an active mechanism to suppress
the accumulation of defense transcripts and phytoalexin biosynthesis in
bean.
