Plant peptidoglycan precursor biosynthesis: Conservation between moss chloroplasts and Gram-negative bacteria

Area of Science:

• Plant Biology
• Biochemistry
• Evolutionary Biology

Background:

• Peptidoglycan synthesis is observed in chloroplasts of many photosynthetic eukaryotes.
• The specific biosynthetic pathway and its evolutionary origin remain largely uncharacterized.

Purpose of the Study:

• To elucidate the peptidoglycan biosynthetic pathway in the chloroplasts of the moss *Physcomitrium patens*.
• To investigate the specificity of amino acid incorporation in this pathway.

Main Methods:

• Utilized mass spectrometry to analyze moss metabolome under antibiotic treatment.
• Employed enzymology to characterize the UDP-N-acetylmuramoyl-L-alanyl-D-glutamate-2,6-diaminopimelate ligase (MurE) from moss and cyanobacteria.

Main Results:

• Identified elevated levels of five peptidoglycan pathway intermediates in *P. patens*.
• Demonstrated that *P. patens* MurE ligase preferentially incorporates D,L-diaminopimelic acid (D,L-DAP), similar to Gram-negative bacteria.
• Showed catalytic efficiency of *P. patens* MurE comparable to bacterial homologs.

Conclusions:

• The study provides strong evidence for a conserved peptidoglycan biosynthesis pathway in moss chloroplasts.
• The preference for D,L-DAP suggests a link to Gram-negative bacterial peptidoglycan synthesis.
• Results support the hypothesis of a horizontal gene transfer event contributing to this pathway in plants.