Plants genetic makeup ensures their survival. Despite having no immune system plants can resist infection by constitutive or induced defense mechanism. The synthesis of plant protein induced due to pathological or related situation are referred to as pathogenesis-related (PR) protein (Antoniw et al., 1981). PR protein play an important role in induced resistance and are also accumulated on mechanical wounding (Chang et al., 1995) and abiotic stresses (Ernst et al., 1992; Green and Fluhr 1995). The physicochemical properties of PR proteins enables them to resist the acidic pH and proteolytic cleavage thus ensuring their survival in vacuolar compartment or cell wall or intercellular spaces (Stintzi et al., 1993).  Plant pathogen and insect elicit PR protein biosynthesis and affect their development (Conrads-Strauch et al., 1990; Ryan 1990). Most PR proteins are induced through the action of the signaling compounds salicylic acid, jasmonic acid, or ethylene and possess antimicrobial activities (van Loon et al., 2006). The rhizosphere microorganisms or some plant growth promoting rhizobacteria induce PR proteins (Park and Kloepper 2000). Though 17 families of pathogenesis-related proteins have been classified. The 14 families of PR protein (van Loon and van Strien 1999) mentioned are as follows:

PR-1 found to display differential fungicidal activity (Niderman et al., 1995).

The PR-2 family consists of endo- β-1,3-glucanases and PR-3, PR-4, PR-8 and PR-11 are all classified as endochitinases. Type of chitinases are distinguished by class i.e. based on their activities over a wide range of substrate. Class III (PR-8) are basic isoform possessing substantial lysozyme activity. Chitinases and β-1,3-glucanases degrade fungal cell wall.

PR-5 belongs to thaumatin-like proteins (homology to permatin), permeabilize fungal membrane (Vigers et al., 1991).

PR-6 are proteinase inhibitors. They are involved in defense against insect, other herbivores, microorganisms and nematodes (Koiwa et al., 1997; Ryan 1990).

PR-7 acts as endoproteinase. Lysis of cell wall i.e. degradation of cell wall protein in addition to hydrolysis of chitin and glucan (Haran et al., 1996).

PR-9 strengthens plant cell wall by catalyzing lignin deposition in response to microbial attack. Peroxidases in plant cell is associated with lignin biosynthesis in response to pathogen attack (Ostergaard et al., 2000).

PR-10 is structurally related to ribonucleases.

PR-12 are plant defensins (antimicrobial activities).

PR-13 protein are thionins (antimicrobial activities). The electrostatic interaction of the positively charged thionin with the negatively charged phospholipids making up the membrane forms pore which leads to disruption of the membrane (Florack and Stiekema 1994).

PR-14 are lipid transfer proteins (LTPs). They exhibit antifungal and antibacterial activity. LTPs are active plant-defense protein (García-Olmedo et al., 1995).

In some cases PR-4 and PR-10 exhibit ribonuclease activity and this activity is related to their fungicidal properties. These proteins inhibit the growth of fungi (Filipenko et al., 2013). The antifungal activity of PR-ribonucleases have cytotoxic impact by degrading the mRNA pool of fungi (penetration of nucleases into the cell of the pathogen) as well as the PR- ribonucleases participate in induction of plant cell apoptosis leading to hypersensitive responses restricting the spread of the pathogen (Filipenko et al., 2013).

Compost made up of agricultural residue provide protection against soil –borne pathogens (Hoitink et al., 1996; Hoitink and Boehm 1999). The compost mediated induced resistance may be due to the activation of plant defense related genes and accumulation of peroxidases, β-1,3-glucanases and pathogenesis–related protein PR-1 (Zhang et al., 1998; Kavroulakis et al., 2005). Colonization of plant with rhizobacteria leads to induced systemic resistance (ISR) providing protection against pathogen. The rhizosphere fungi and bacteria exhibit antagonistic property. Kavroulakis et al., (2006) reported that expression of PR genes may be triggered by the microflora of the compost or could be associated with abiotic factor of the compost. Though the PR protein role in plant defense has been studied but there are few PR proteins whose biological functions are unknown.



Antoniw, J. F., Kueh, J. S. H., Walkey, D. G. A. and White, R. F. 1981 The Presence of Pathogenesis-Related Proteins in Callus of Xanthin-nc tobacco. Phytopathol.  Z 101: 179 – 184

Chang, M-M., Horovitz, D., Culley, D. and Hadwiger, L. A. 1995 Molecular Cloning and Characterization of a Pea Chitinase Gene Expressed in Response to Wounding, Fungal Infection and the Elicitor Chitosan. Plant Mol. Biol. 28(1): 105 – 111

Conrads-Strauch, J., Dow, J. M., Milligan, D. E., Parra, R. and Daniels, M. J. 1990 Induction of Hydrolytic Enzymes in Brassica campestris in response to Pathovars of Xanthomonas campestris. Plant Physiol. 93: 238 – 243

Ernst, D., Schraudner, M., Langbartels, C. and Sandermann Jr.,  H. 1992 Ozone-Induced Changes of mRNA Levels of β-1,3-glucanase, Chitinase and Pathogenesis-Related Protein 1b in Tobacco Plants. Plant Mol. Biol. 20(4): 673 – 682

Filipenko, E. A.,  Kochetov,  A. V., Kanayama,  Y.,  Malinovsky,  V. I. and Shumny, V. K. 2013 PR-Proteins with Ribonuclease Activity and Plant Resistance Against Pathogenic Fungi. Russian Journal of Genetics: Applied Res. 3(6): 474–480

Florack, D. E. and Stiekema, W. J. 1994 Thionins: Properties, Possible Biological Roles and Mechanisms of Action. Plant Mol.  Biol. 26(1):25-37

García-Olmedo, F., Molina, A., Segura, A. and Moreno, M. 1995 The Defensive Role of Nonspecific Lipid-Transfer Proteins in Plants. Trends in Microbiol. 3(2): 72–74

Green, R. and Fluhr, R. 1995 UV-B-Induced PR -1 Accumulation is Mediated by Active Oxygen Species. The Plant Cell 7: 203 – 212

Haran, S., Schickler, H. and Chet, I. 1996 Molecular Mechanisms of Lytic Enzymes Involved in the Biocontrol Activity of Trichoderma harzianum. Microbiology 142: 2321–2331

Hoitink, H. A. J., Stone, A. G. and Han, D. Y. 1996 Suppression of Plant Diseases by Composts. Hort Science 32(2): 184–187

Hoitink, H. and Boehm, M. 1999 Biocontrol within the Context of Soil Microbial Communities: A Substrate-Dependent Phenomenon. Annu Rev Phytopathol. 37:427-446

doi: 10.1146/annurev.phyto.37.1.427

Kavroulakis, N., Ehaliotis, C., Ntougias, S., Zervakis, G. I. and  Papadopoulou,  K. K. 2005  Local and Systemic Resistance Against Fungal Pathogens of Tomato Plants Elicited by a Compost Deriving from Agricultural Residues. Physiol. Mol. Plant Pathol.  66: 163–174

Kavroulakis, N., Papadopoulou, K. K., Ntougias, S., Zervakis, G. I. and Ehaliotis C. 2006 Cytological and Other Aspects of Pathogenesis-related Gene Expression in Tomato Plants Grown on a Suppressive Compost.  Ann. Bot. 98(3): 555–564

doi:  10.1093/aob/mcl149

Koiwa, H., Bressan, R. A. and  Hasegawa, P. M. 1997 Regulation of Protease Inhibitors and Plant Defense. Trends in Plant Science 2(10): 379–384

Niderman, T., Genetet, I., Bruyère, T., Gees, R., Stintzi, A., Legrand, M., Fritig, B. and Mosinger, E.  1995 lsolation and Characterization of Three 14-Kilodalton Proteins of Tomato and of a Basic PR-1 of Tobacco with lnhibitory Activity against Phytophthora infestans. Plant Physiol. 108: 17-27

Ostergaard, L., Teilum, K., Mirza, O., Mattsson, O., Petersen, M., Welinder, K. G., Mundy, J., Gajhede, M. and Henriksen, A. 2000 Arabidopsis ATP A2 peroxidase. Expression and high-resolution structure of a plant peroxidase with implications for lignification. Plant Mol Biol. 44(2): 231-243

Park, K. S. and Kloepper, J. W. 2000 Activation of PR-1a Promoter by Rhizobacteria that Induce Systemic Resistance Against Pseudomonas syringae pv. tabaci. Biol. Control 18: 2–9


Ryan,  C. A. 1990. Protease Inhibitors in Plants: Genes for Improving Defenses Against Insects and Pathogens. Annu. Rev. Phytopathol. 28: 425–449

Stintzi, A., Heitz, T., Prasad, V., Wiedemann-Merdinoglu, S., Kauffmann, S., Geoffroy, P., Legrand, M. and Fritig, B.  1993 Plant Pathogenesis-Related Proteins and Their Role in Defense Against Pathogens. Biochimie. 75(8): 687-706

van Loon, L. C. and van Strien, E. A. 1999 The Families of Pathogenesis-related Proteins, Their Activities, and Comparative Analysis of PR-1type Proteins. Physiol. Mol. Plant Pathol. 55: 85-97

van Loon, L. C., Rep, M. and Pieterse, C. M. J. 2006 Significance of Inducible Defense-related Proteins in Infected Plants. Annu. Rev.  Phytopathol.  44:135-162

Vigers, A. J., Roberts, W. K. and Selitrennikoff, C. P. 1991 A New Family of Plant Antifungal Proteins. Mol. Plant-Microbe Interactions 4: 315–323

Zhang, W., Han, D. Y., Dick, W. A., Davis, K. R. and Hoitink, H. A. J. 1998 Compost and Compost Extract-Induced Systemic Acquired Resistance in Cucumber and Arabidopsis. Phytopathology 88(5): 450–455

doi: 10.1094/PHYTO.1998.88.5.450

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