Plant Molecular Biology 43: 429–438, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
cDNA cloning and characterization of a plant protein that may be
associated with the harpin
-mediated hypersensitive response
, Hao-jan Lin
, Mang-jye Ger
and Teng-yung Feng
Institute of Botany, Academia Sinica, Taipei 115, Taiwan (
author for correspondence; e-mail: bofeng@cc vax.
Institute of Life Science, National Defense Medical Center, Taipei, Taiwan
Received 27 July 1999; accepted in revised form 8 March 2000
Key words: defense-related protein, harpin
, hypersensitive response, hypersensitive response-assisting protein,
Hypersensitiveresponse-assistingprotein(HRAP)is a novelplant proteinthat can intensifythe harpin
hypersensitive response (HR) in harpin
-insensitive plants, such as the vegetative stage of sweet pepper. In this
report, we identiﬁed a HRAP cDNA clone from sweet pepper (Capsicum annuum cv. ECW). The sequence of
this cDNA clone showed no appreciable similarity to any other known sequences. However, it contained three
positively charged regions, a typical signal peptide and a cAMP-dependent phosphorylation site. The hrap mRNA
accumulatedpreferentially during the incompatible interaction of sweet pepper leaves with a pathogenic bacterium,
Pseudomonas syringae pv. syringae. When the hrap gene transcription level was high, the sweet pepper leaves
readily expressed the harpin
-mediated HR. The hrap gene transcription level in sweet pepper was also higher
during the reproductive stage than during the vegetative stage. The HRAP distribution in an individual plant and
different plant species was investigated. We found that all the organs of sweet pepper, except fruit, could express
two different forms of HRAP. Moreover, the hrap gene was presented in many plant species including tobacco,
Arabidopsis, and rice. In conclusion, our results suggest that the hrap gene is widely distributed throughout the
plant world and its transcription level correlates with plant sensitivity to harpin
. The interaction between HRAP
reveals a novel way to interpret the interaction mechanism between plants and bacterial pathogens.
The hypersensitive response (HR), characterized by
the rapid, localized death of plant cells at the site
of pathogen invasion (Klement et al., 1964; Tuner
and Novacky, 1974; Goodman and Novacky, 1994),
is an important defense response to prevent further
multiplication and restrict the spread of the pathogen
in plant tissue. The ability of many Gram-negative
plantpathogens,such as Pseudomonas, Xanthomonas,
and Erwinia, to elicit a HR or cause a disease in
plants is controlled by hrp genes (Bonas, 1994).
Many hrp genes encode components of a type III
protein secretion system conserved in both plant and
The nucleotide sequence data reported will appear in the
EMBL and GenBank Nucleotide Sequence Databases under the
accession number AF168415 (hrap cDNA).
animal pathogens (Galán and Collmer, 1999). One
protein known to be secreted by the Hrp system is
, encoded by hrpZ in the hrp gene clus-
ter from Pseudomonas syringae pv. syringae (He
et al., 1993). Harpin
is capable of eliciting a HR
when inﬁltrated into the leaf intercellular spaces of
tobacco and several other plants (He et al., 1993).
Two pieces of evidence to support that harpin
can interact with molecules on the plant cell surfaces
and induce HR through membrane signal transduction
pathways were previously reported. First, harpin
mediated HR could be prevented or delayed by in-
hibitors of membrane signal transduction in tobacco
(He et al., 1993). Second, Hoyos et al. (1996) reported
that ﬂuorochrome-tagged harpin
the outer portion of the plant cell surface under the
-HR induction of tobacco suspension cells.