Figure 3. Proposed biosynthetic pathway of GM and GGM in Dendrobium stem.
The biosynthetic pathway was modified according to the pathways proposed in Amorphophallus konjac31,32. GM or GGM biosynthesis is supposed to be generated from sucrose, mainly produced by photosynthesis in the leaf tissue (Supplementary Note 7). The enzymes indicated in red are highly expressed in the stem. Only abbreviations of gene names are shown: Csl, Cellulose synthase like gene; FRK, fructokinase; Fru, fructose; Fru-6-P, Fructose-6-phosphate; GGP, GDP-glucose-pyrophosphorylase; GMPP, GDP-mannose pyrophosphorylase; GT, glycosyltransferase; HXK, hexokinase; INV, invertase; MSR, mannan synthesis-related; PGI, phosphoglucose isomerase; PGM, phosphoglucomutase; PMI, phosphomannose isomerase; PMM, phosphomannomutase; RWA, Reduced Wall Acetylation proten; SuS, sucrose synthase; UGE, UDP-galactose epimerase; UGP, UDP-glucose pyrophosphorylase.