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Genomics and Applied Biology
, 2012, Vol.3 No.2 8-21
http://gab.sophiapublisher.com
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Table 1 Plant proteinase inhibitor family in
PLANT-Pis
Plant protease inhibitor family
PLANT-PIs
code
Bowmann-Birk serine proteinase inhibitors
BBI
Cereal trypsin / α-amylase inhibitors
BRI
Cysteine proteinase inhibitors
CYS
Metallo carboxypeptidase inhibitors
MCI
Mustard trypsin inhibitors
MSI
Potato type I inhibitors
PI1
Potato type II proteinase inhibitors
PI2
Serpin
SP1
Soybean trypsin inhibitors (kunitz)
KNI
Squash inhibitors
SQI
However, their occurrence in aerial part of plants,as a
consequence of several stimuli, has also been
documented (De Leo et al., 2002). PIs accumulate to
about 1 to 10% of the total soluble proteins of storage
tissues. Number of PIs has been reported from
non-storage tissues, such as leaves, flowers and roots
(Brzin and Kidric, 1995; Xu et al., 2001; Sin and Chye,
2004). Trypsin inhibitor in mung bean is found
localized to cytosol of cotyledonary cells (Chrispeels
and Baumgartner, 1978). Soybean trypsin inhibitor
(SBTI) was found localized in cotyledonary cell walls
and embryonic cells, and to lesser extent in protein
bodies, cytoplasm and nuclei. Soybean Bowman- Brik
inhibitor (SBBI) was found to occur in protein bodies,
nuclei,
and
cytoplasm
(Horisberger
and
Tacchini-Vonlanthen, 1983). In tomatoes, serine
proteinase inhibitors I and II selectively accumulated in
endosperm and secretory cells of root cap
(Narwaez-Vasquez et al., 1993). Xu et al (2004)
reported the expression of phloem specific PIN2
protein in S. americanum stems, roots, and leaves.
3 Properties and regulation of plant PIs
Plants PIs are typical polypeptides composed of
L-amino acids linked through peptide bonds,
widespread in both monocots and dicot species (Ryan,
1990). Although the molecular size of PIs varies
from 4 to 85 kD, majority of them are in the range of
8 kD to 20 kD (Hung et al., 2003). Plant PIs usually
have high cysteine residues that form disulfide bridges
contributing significantly to the stability of the
inhibitors. Bowman-Birk type of Trypsin inhibitor
from Brassica campestris seed (BCTI) of molecular
size 8 kD, was found to be thermo stable, which is
apparently related to the presence of the disulfide
bridge (Hung et al., 2003). Plant PIs are low in
methionione, histidine and tryptophan but are often
rich in aspartic acid, glutamic acid, serine, arginine
and lysine. Glycosylated plant PIs similar to
mammalian glycoprotein proteinase inhibitors have
not been reported so far.
Systemic signals associated with translocation of
wound response include systemin, abscisic acid
(ABA), hydraulic (variation potentials) andelectrical
signals (Malone and Alarcon, 1995). In tomato, it has
been shown that protease inhibitor initiation factor
(PIIF) is wound inducible, triggers the cascade of
events leading to the synthesis of serine proteinase
inhibitor in the whole plant (Bryant et al., 1976;
Miège et al., 1976). This suggests the existence of
signal that moves from injured tissue to all parts of the
plant leading to systematic induction of PI gene
expression. Systemin regulates the activation of over
20 defensive genes in tomato, in response to herbivore
and pathogen attack, by activating lipid based signal
transduction pathway- linolenic acid released from
plant membranes is converted into signaling molecule,
jasmonic acid (JA). Systemin, cell surface receptor of
molecular size~160 kD, regulates intercellular cascade
by (1) depolarization of the plasma membrane and (2)
opening of ion channels, thus increasing the
intracellular Ca
2+
, which activates MAPK and
phospholipase A. These rapid changes play vital role
in intra cellular release of membrane linolenic acid
and its conversion to JA, potent transcription activator
of defense gene (Koiwa et al., 1997; Ryan, 2000).
Plantinfected by pathogen trigger two possible signal
pathways as its defense strategy- (1) recognition of
penetration and colonization of pathogen through
wound and (2) direct molecular recognition of the
pathogen (Figure 1; Figure 2) (Cordero et al., 1994).
Salicylic Acid (SA) and its methyl ester (MeSA)
induce systemic acquired resistance in plants against
pathogenic microorganisms (Hunt et al., 1996).
Several jasmonic acid-dependent and independent
wound signal transduction pathways have been
identified and characterized. Components of these
signaling pathways are similar to other signaling
cascades that include reversible protein phosphorylation
cascade, calcium/calmodulin- regulated events and
production of reactive oxygen species (León et al.,
2001). Stintzi et al (2001) demonstrated that in absence
of JA, 1, 2-oxo- phytodienoic acid (OPDA), precursor
of JA, elicits defense signal response. Induced rapid de
novo synthesis of rice BBI was found in seedling/leaf