Fig 1. Hypothetical metabolic reconstruction of Buchnera PGN metabolism with potential involvement of aphid HTGs in the Aphidinae subfamily (including tribes Macrosiphini and Aphidini).

PGN metabolism is divided into four pathways: PGN recycling and lipid II synthesis in the cytoplasm, and cell wall synthesis and remodeling in the periplasm. Arrows depict enzymatic reactions, with black, gray, and white colors indicating complete, sporadic, or no conservation of the responsible gene(s) among ten Buchnera genomes. Light and dark green arrows denote incomplete and complete conservation of host HTGs. For PGN cartoons, dark and light brown indicate GlcNAc and MurNAc glycans, respectively, while black-ended light brown indicates anhydro-MurNAc. Stem peptides consist of l-Ala (dark blue), iso-d-Glu (green), meso-diaminopimellic aicd (mDap) (maroon), and d-Ala (light blue) amino acids. For lipid II, the phosphate groups of undecaprenyl-diphosphate are shown in pink.