Lecture 15: Plant Cell Wall Attachment

Define papilla

Dome shaped apposition between the epidermal wall and plasma membrane at point of attempted penetration by fungal pathogens. Common but not a unviersal response to pathogen attack, mainly during penetration. 

Define lignification

Lignin (polyphenolic polymer) accumulated on the wallof cells under pathogen’s attack. Naturally in component of woody plants and vascular tissue of herbaceous plants

What is the principal component of papillae?

Callose is prinicpal component and vesicle trafficking is important in induction/formation

What is the role of papillae in resistance?

Believed to provide physical and chemical barriers to halt penetration of pathogens. Form in both R and S reactions but form in ressitant lines faster, larger, uniform and having more biochemical compounds. Chemically induced large papillae more effective in halting pepentration than normal sized papillae. Can be effective or ineffective

What is the effective papilla hypothesis?

Effective pipilla has a layered structure with phenols in its core and callose adn arabinoxylans through the body of the papilla and an outer capsulation by arabinoxylan and cellulose (cellulose → callose and arabinoxylans → phenol)

Give an example of papilla in plant resistance

* RNAi of GSL5 led to no callose formation, and slight increase in penentration in Bgh infection
* GSL5 is involved in haustorial complex formation 
* Overexpression GSL5 produced bigger papilla
* PEN1 (SNARE protein) confers non host resistance of Arabidopsis to barley powdery mildew
* PEN1 is part of a secretory pathway for building papilla: mediates membrane fusion

What are the various lignin monomers

* P-courmary (H lignin)
* Confieryl alcohol (S lignin)
* Sinapyl alcohol (G lignin)

Explain lignin biosynthesis

Genes involved in biosynthesis pathways are usually up-regulated during pathogen attacks (ex: PAL). Blocking of biosyhthetic enzymes or disruption of and/or other antimicrobial compounds, thus comprinising the defense response. Cases in that reducing ligning or other componenets increased resistance to certain pathogens

What is the possible role of lignin in resistance?

Lignified walls are stronger mechanistically which suggests ligning is a mechanical barrier to penetration. Ligning masks cell wall polysaccharides (pectin) from enzymes from the pathogen (pectinases) making cell wall less susceptible to degradation. Lignified walls act as a diffusion barrier to keep out toxins, enzymesm and other pathogen metabolites and to keep in host nutrients. Ligning precursors (intermediates in the phenylpropanoid pathway) and associated free radicals are toxic to the pathogen. Pathogen itself can become lignified