Perception of PGN

Perception of the bacterial Microbe-Associated Molecular Patterns (MAMPs), peptidoglycan and muropeptides, from pathogens Xanthomonas and Agrobacterium

 

Using two Gram-negative plant pathogens we have shown that the bacterial structural cell wall component peptidoglycan (PGN) from Xanthomonas campestris pv. campestris (Xcc) and Agrobacterium tumefaciens (At) act as MAMPs and trigger the innate immune response in Arabidopsis. Muropeptide fragments of PGN were significantly more effective than the intact PGN molecule. PGN and its fragments from Xcc were more potent defence elicitors than those from At, possibly reflecting the biotrophic mode of parasitism of the latter.  Furthermore, differences in the structures of Xcc and At muropeptides were observed; a glycine residue replacing an alanin in the case of At PGN and a lack of an acetyl group in the case of Xcc PGN (Erbs et al., 2008).

 

In this project the role of PGN in triggering innate immunity in plants is further studied. Knowledge about the differences in the chemical nature of Xcc and At PGN together with findings of what the truly active part of the PGN molecule from Xcc and At, respectively, is, will be valuable in the further search of PGN recognition receptors.

 

Fig. 1. General structural architecture of peptidoglycan (PGN). PGN, found in both Gram-positive and Gram-negative bacteria, has a glycan backbone made up of a repeat polymer of two amino sugars, N-acetylglucosamine (G) and N-acetylmuramic acid (M). Attached to the N-acetylmuramic acid is a peptide side chain consisting of a peptide moiety displaying considerable diversity. In general, the third position amino acid in Gram-positive bacteria is L-lysine (Lys) while in Gram-negative bacteria it is meso-2,6-diaminopimelic (DAP) acid. Furthermore, Gram-positive bacteria have peptide stems usually crosslinked through an interpeptide bridge (generally glycine) whereas Gram-negative bacteria peptide stems are usually directly crosslinked. Muropeptides derived from peptidoglycan of Gram-negative pathogens. a: Xanthomonas campestris pv. campestris (Xcc); b: Agrobacterium tumefaciens (At); Differences between the structures are indicated in the green boxes; in At a glycine containing muropeptide was observed whereas in Xcc alanine is present. In Xcc an N-deacetylated GlcN is present rather than the GlcNAc found in At.

 

Reference 

Erbs, G., Silipo, A., Aslam, S., De Castro, C., Liparoti, V., Flagiello, A., Pucci, P., Lanzetta, R., Parrilli, M., Molinaro, A., Newman, M.-A. And Cooper, R.M. (2008). Peptidoglycan and muropeptides from pathogens Agrobacterium and Xanthomanas elicit innate immunity: structure and activity. Chemistry and Biology 15: 1-11.

 

Funding 

This project is funded by the Danish Research Council for Independent Research; Technology and Production Sciences (FTP).