FORTIFICATION OF CELL WALL IS A PLANT DEFENSE MECHANISM

The plant cell wall is a complex structure and its functional integrity is maintained during interactions with the environment. Plants have cell wall integrity sensing mechanism by which they may detect pathogen attack triggering signaling pathways that induces rapid defense responses (Hématy et al., 2009). The first barrier that the pathogen encounter is the cuticle and the cell wall. In order to gain entry into the plant cell the pathogen disrupt the host cuticle by secreting oxidases, esterases, cutinases, and lipases (Feng et al., 2011). Infection by fungus includes attachment of conidia to the host surface followed by germination on favorable condition producing germ tube that penetrates the host surface killing cells leading to lesion formation, this may activate defense responses. The pathogen have the ability to overcome the defense mechanisms and are able to infect and colonize the plant i.e. fungus grows resulting into tissue maceration followed by sporulation (Prins et al., 2000). Plant cell walls are mainly composed of carbohydrate (polysaccharides such as cellulose, hemicelluloses and pectins), lignin and contain proteins involved in the cell dynamics through diverse functions such as growth, environmental sensing, signaling, and defense (Showalter 1993).

Plants on sensing pathogens and loss of cell wall integrity, activate plant defense responses that lead to cell wall remodeling required to prevent the disease (Bellincampi et al., 2014). Upon invasion by the pathogen, plant improvise defense by strengthening cell wall with lignin, callose and hydroxyl proline-rich-glycoprotein or produce phytoalexin and hydrolytic enzymes. Lignin deposition strengthens the cell wall and maintains functional integrity (Denness et al., 2011). Fortification of cell wall with papilla, callose, lignin and cell wall protein are defense response of plant on sensing pathogen attack.

 Papillae :

The Papillae are heterogeneous material deposited between the plasma membrane and inside of the plant cell wall. These papillae are deposited by plants in response to pathogen penetration and mechanical injury. Papillae composition varies between different plant species. Papillae contain (1,3)-β-glucan callose (most abundant constituent), cellulose, hemicelluloses, pectins, lignin, and structural proteins such as arabinogalactan proteins and hydroxyproline-rich-glycoproteins (HRGPs) (Aist 1976; Celio et al., 2004; Voigt 2014). Different papilla-forming transport processes ensures plant defense (Voigt 2014). Callose-rich papillae is found at sites of pathogen penetration and provides resistance (Aist 1976).

Callose:

Callose is a polysaccharide present in the cell walls of a many higher plants. It is in the form of (1,3)-β-glucan with some β-1,6-branches and is produced by callose synthases (Chen and Kim 2009). Callose is the major component of papillae deposited between the plasma membrane and cell wall to act as a physical barrier to the invading pathogen and is also induced in response to abiotic and biotic stresses (Ellinger and Voigt 2014). Furthermore it is deposited at plasmodesmata to regulate the cell-to-cell movement of molecules by decreasing the size exclusion limit of plasmodesmata (Iglesias and Meins 2000; Bucher et al., 2001) and plays an important role in plant development.

Lignin:

Lignification is the plant defense response and acts as a physical barrier to pathogen invasion providing resistance against the pathogen. Lignin is deposited in secondary wall of most plant cells providing rigidity and mechanical support. Chemically lignin is an aromatic polymer composed of phenylpropanoid monomer mainly of p-coumaryl, coniferyl and sinapyl alcohol. The phenylpropanoid pathway responsible for lignin biosynthesis serves to support the synthesis of other phenolic compounds such as phytoalexins, coumarins, and flavonoids which are involved in plant defense (Dicko et al., 2005; Frasera and Chapplea 2011). Role of lignification in disease resistance has been reviewed by Nicholson and Hammerschmidt (1992). Several component of fungal cell wall are elicitors of lignification.

Cell wall Structural protein:

Structural proteins in plant cell walls are the hydroxyproline-rich-glycoproteins (HRGPs). There are four major group of hydroxyproline-rich-glycoproteins (HRGPs) in plants (Sommer-Knudsen et al., 1998):

• Hydroxy/ Proline-rich-proteins (H/PRPs)
• The solanaceous lectins
• Arabinogalactans protein (AGPs)
• Extensins

HRGPs strengthen the cell wall in response to plant defense. The condition regulating the expression of the five major classes  of cell wall  proteins [extensins, glycine-rich-proteins (GRPs), PRPs, AGPs and solanaceous lectins] are wounding, fungal/ viral infection, fungal/endogenous  elicitors, abiotic stress and development (Showalter 1993).

The multicomposition of plant cell wall can provide some insight to pant-pathogen interaction.

 

References:

Aist, J. R. 1976 Papillae and Related Wound Plugs of Plant Cells.  Annu. Rev. Phytopathol. 14:  145–163

doi.org/10.1146/annurev.py.14.090176.001045

Bellincampi, D. Cervone, F. and Lionetti, V. 2014 Plant Cell Wall Dynamics and Wall-Related Susceptibility in Plant–Pathogen Interactions. Front Plant Sci. 5: 228

doi:  10.3389/fpls.2014.00228

Bucher, G. L., Tarina, C., Heinlein, M., Serio, F. D., Meins, F. Jr. and  Iglesias,  V. A. 2001 Local Expression of Enzymatically Active Class 1 β-1,3-glucanase Enhances Symptoms of TMV Infection in Tobacco. The Plant J. 28(3): 361–369

10.1046/j.1365-313X.2001.01181.x

Celio, G. J., Mims, C. W. and Richardson, E. A. 2004 Ultra-Structure and Immuno Cytochemistry of the Host–Pathogen Interface in Poinsettia Leaves Infected with Powdery Mildew. Can. J. Bot. 82(4): 421–429

10.1139/b04-019

Chen, X-Y. and Kim, J-Y. 2009 Callose Synthesis in Higher Plants.  Plant Signal Behav. 4(6): 489–492

doi:  10.4161/psb.4.6.8359

Denness, L., McKenna, J. F., Segonzac, C., Wormit, A., Madhou, P., Bennett, M., Mansfield, J., Zipfel, C. and Hamann, T. 2011 Cell Wall Damage-Induced Lignin Biosynthesis is Regulated by a Reactive Oxygen Species- and Jasmonic Acid-Dependent Process in Arabidopsis1,[C][W][OA]. Plant Physiol. 156(3): 1364–1374

doi:  10.1104/pp.111.175737

Dicko, M. H., Gruppen, H., Barro, C., Traore, A. S., van Berkel, W. J. and  Voragen, A. G. 2005 Impact of Phenolic Compounds and Related Enzymes in Sorghum Varieties for Resistance and Susceptibility to Biotic and Abiotic Stresses. J. Chem. Ecol. 31(11): 2671–2688

10.1007/s10886-005-7619-5

Ellinger, D. and Voigt, C.  A. 2014 Callose Biosynthesis in Arabidopsis with a Focus on Pathogen Response: What We Have Learned Within the Last Decade.  Ann.  Bot. 114(6): 1349–1358

doi:  10.1093/aob/mcu120

Feng, J., Wang, F., Hughes, G. R., Kaminskyj, S. and Wei, Y.  2011 An Important Role for Secreted Esterase in Disease Establishment of the Wheat Powdery Mildew Fungus Blumeria graminis f. sp tritici. Can. J. Microbiol. 57(3):  211–216

10.1139/W10-120

Frasera, C. M. and Chapplea, C.  2011 The Phenylpropanoid Pathway in Arabidopsis. Arabidopsis Book. 9: e0152

doi:  10.1199/tab.0152

Hématy, K., Cherk, C. and Somerville, S. 2009 Host-Pathogen Warfare at the Plant Cell Wall. Curr. Opin.  Plant Biol. 12(4): 406-413

doi: 10.1016/j.pbi.2009.06.007

Iglesias, V. A. and Meins, F. Jr.  2000 Movement of Plant Viruses is Delayed in a β-1,3-glucanase-Deficient Mutant Showing a Reduced Plasmodesmatal Size Exclusion Limit and Enhanced Callose Deposition. The Plant J. 21(2): 157–166

doi: 10.1046/j.1365-313x.2000.00658.x

Nicholson, R. L. and Hammerschimdt, R. 1992 Phenolic Compounds and Their Role in Disease Resistance. Annu. Rev. Phytopathol. 30: 369 – 389

doi.org/10.1146/annurev.py.30.090192.002101

Prins, T. W., Tudzynski, P., Von Tiedemann, A., Tudzynski, B.,  Have, A. T, Hansen, M. E., Tenberge, K. and Van Kan J. A. L. 2000 Infection Strategies of Botrytis cinerea and Related Necrotrophic Pathogens  In “Fungal Pathology” (J. W Kronstad ed.) Kluwer Academic Publishers / Springer-Science+Business Media B. V.  Chapter 2:  33–64

doi: 10.1007/978-94-015-9546-9_2

Showalter, A. M. 1993 Structure and Function of Plant Cell Wall Proteins. The Plant Cell 5: 9-23

doi: 10.1105/tpc.5.1.9

Sommer-Knudsen, J., Bacic, A. and Clarke, A. E. 1998 Hydroxyproline-Rich Plant Glycoproteins. Phytochem. 47(4): 483 – 497

doi.org/10.1016/S0031-9422(97)00724-3

Voigt, C. A. 2014 Callose-Mediated Resistance to Pathogenic Intruders in Plant Defense-Related Papillae.  Front Plant Sci. 5: 168

doi:  10.3389/fpls.2014.00168