Peptidoglycan in eukaryotes: Unanswered questions

Peptidoglycan has been retained in chloroplasts that have evolved from cyanobacteria along some evolutionary tracks, but has seemingly been quickly eliminated during evolution of others. It has been eliminated in Rhodophyta, Chlorophyta, Pteridophyta and Spermatophyta, but has been retained in streptophyte algae, Glaukophyta, and Lycophyta. In this article questions emerging from this are raised, and for some of them answers are suggested. [Display omitted] •Peptidoglycan is thought of as being a component specific for bacteria.•It occurs also in chloroplasts of glaucophytes, some algae, and some bryophytes.•It is probably present also in lycophytes, but not in ferns and seed plants.•The reasons for the phylogenetic distribution of peptidoglycan are discussed.