Plant Science 156 2159 23 – 34
Pepper gene encoding a basic b-1,3-glucanase is differentially expressed in pepper tissues upon pathogen infection and ethephon
or methyl jasmonate treatment
Ho Won Jung, Byung Kook Hwang
Molecular Plant Pathology Laboratory, Department of Agricultural Biology, Korea Uni6ersity, Seoul
136
-
701
, South Korea Received 21 February 2000; received in revised form 17 May 2000; accepted 3 July 2000
Abstract
A basic b-1,3-glucanase cDNA clone CABGLU was isolated from the cDNA library constructed from hypersensitive response lesions of pepper leaves infected with avirulent strain of Xanthomonas campestris pv. 6esicatoria. The deduced polypeptide of
CABGLU which contains a C-terminal extension N-glycosylated at a single site characterized as typical structure of class I b-1,3-glucanase has a high level of identity with tobacco basic b-1,3-glucanase 77.4, but only a moderate level of identity with
tomato acidic b-1,3-glucanase 42.6. Genomic DNA gel blot analysis indicates that the pepper genome contains one or two b-1,3-glucanase copy genes. Transcripts of the CABGLU gene were more induced in incompatible interactions than in compatible
interactions, when inoculated with X. campestris pv. 6esicatoria or Phytophthora capsici. Accumulation of CABGLU mRNA was strongly induced in pepper leaves by both ethephon and methyl jasmonate. The CABGLU mRNA was constitutively expressed
only in the roots of all the plant organs. These data indicate that the basic b-1,3-glucanase gene may be induced by pathogen attack and abiotic stresses. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Basic b-1,3-glucanase; Capsicum annuum; Ethephon; Methyl jasmonate; Phytophthora capsici; Xanthomonas campestris pv. 6esicatoria www.elsevier.comlocateplantsci
1. Introduction
Plants respond to pathogen attack or external environmental stresses by producing a diverse set
of proteins. These proteins, which have been most extensively studied in tobacco plants infected with
tobacco mosaic virus TMV, are commonly re- ferred to as pathogenesis-related PR proteins [1].
In particular, chitinase and b-1,3-glucanase have long been suggested to be associated with the
antifungal defenses of plants [2,3]. b-1,3-Glucanase hydrolyses the b-1,3-linked glucans, major compo-
nents of cell wall of oomycetes and synergistically acts with chitinase to inhibit fungal growth in
vitro [3,4]. The enzyme may also mediate in plant defense by releasing glucan fragments from fungal
or plant cell walls as signal molecules that can activate a variety of plant defenses [5,6]. In addi-
tion to pathogen attack, the expression of b-1, 3-glucanases has been shown to be induced by
abiotic elicitors such as ethylene [6], salicylic acid [7], and methyl jasmonate [8]. Additionally, b-1,3-
glucanases have been involved in several physio- logical and developmental processes such as
microsporogenesis [9], seed germination [10], pol- len development [11], and fruit development
[12].
b-1,3-Glucanase has been demonstrated to exist in multiple isoforms in a number of plant species
Nucleotide and amino acid sequence data has been deposited in EMBLGenBank database under accession number AF227953.
Corresponding author. Tel.: + 82-2-32903061; fax: + 82-2- 9251970.
E-mail address
:
bkhwangmail.korea.ac.kr B.K. Hwang. 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 3 3 4 - 4
including tobacco [13], potato [14], bean [15], and rice [16]. In our earlier study, two acidic b-1,3-glu-
canase isoforms and six basic b-1,3-glucanase iso- forms were detected in pepper stems infected with
Phytophthora capsici [17]. We further isolated a b-1,3-glucanase with antifungal activity from pep-
per stems [4]. The two acidic and six basic b-1,3- glucanases were also induced and accumulated in
pepper leaves infected with Xanthomonas campes- tris pv. 6esicatoria [18]. However, the role of b-1,3-
glucanase either in defense responses or in physiological and developmental processes has not
been well understood, since the enzyme activity exists in several isoforms that differ in amino acid
sequences, cellular localization and inducibility [19].
Based on amino acid sequence identities, b-1,3- glucanases from tobacco have been classified into
three structural classes [20]. The class I b-1,3- glucanase is approximately 33 kDa, basic proteins,
and accumulates intracellularly at a site presumed to be vacuoles [21]. This vacuolar localization
correlates with the presence of a distinctive C-ter- minal extension that contains sorting information
for proper targeting to the vacuole [19]. Class II b-1,3-glucanase includes the acidic isoforms such
as PR-2a, PR-2b, and PR-2c, formerly named PR-2, PR-N, and PR-O, respectively [13,20]. The
single representative of the class III isoforms is PR-Q’ found in TMV-infected tobacco leaves [20].
Both class II and III b-1,3-glucanases accumulate predominantly in the extracellular space, i.e. the
apoplast. In some cases, the acidic b-1,3-glu- canases were shown to be present in intercellular
washing fluid IWF from pepper tissues infected with pathogens [17,18].
To gain a better understanding of the role of PR-proteins including b-1,3-glucanase, we con-
structed a cDNA library from pepper leaves infected with avirulent strain Bv5-4a of X. campes-
tris pv. 6esicatoria [22]. More recently, some PR-gene clones encoding b-1,3-glucanase, chiti-
nase, thionin, and lipid transfer protein were isolated from this cDNA library using the differ-
ential hybridization technique [23]. In this paper, we report on the isolation and sequence analysis of
a full-length cDNA clone encoding a basic b-1, 3-glucanase from pepper leaves. We further show
that expression of the basic b-1,3-glucanase gene is induced in pepper leaves and stems by pathogen
infection and abiotic elicitor treatments.
2. Materials and methods
