Description
Vanillin is a popular and valuable flavour compound. It is the key constituent of the naturalvanilla flavour obtained from cured vanilla pods. A single hydratase/lyase type enzyme designated vanillin synthase (VpVAN) catalyses direct conversion of ferulic acid and its glucoside into vanillin and its glucoside, respectively. The enzyme shows high sequence similarity to cysteine proteinases and is specific to the substitution pattern at the aromatic ring and does not metabolize caffeic acid and p-coumaric acid as demonstrated by
coupled transcription/translation assays. VpVAN is highly expressed in the inner light green mesocarp of the vanilla pod and the VpVAN enzyme is localized in senescent chloroplasts or fully re-differentiated chloroplasts termed phenyloplasts, that are formed during pod maturation and are the site of vanillin glucoside accumulation at molar concentrations. In the developing pod, VpVAN is present as the mature form (25 kDa) but, depending on the tissue and isolation procedure, small amounts of the immature unprocessed form (40 kDa) and putative oligomers (50, 75 and 100 kDa) may be observed by immunoblotting using an antibody specific to the C-terminal sequence of VpVAN. Isolated chloroplasts were shown to convert administered [14C]phenylalanine and [14C]cinnamic acid into [14C]vanillin glucoside, indicating that the entire vanillin de novo biosynthetic machinery converting phenylalanine to vanillin glucoside is operating in the chloroplast. Transient expression of VpVAN in tobacco and stable expression in barley in combination with the action of endogenous alcohol dehydrogenases and UDP-glucosyltransferases result in vanillyl alcohol glucoside formation from endogenous ferulic acid. A gene encoding an enzyme showing 71% sequence identity to VpVAN was identified in another vanillin-producing plant species Glechoma hederacea and was also shown to be a vanillin synthase as demonstrated by transient expression in tobacco.
| Period | 12 Nov 2019 |
|---|---|
| Event title | International Symposium for Application of Non-Ornamental Orchids: 88 Anniversary Activity of National Cheng Kung University, Tainan, Taiwan |
| Event type | Conference |
| Location | Tainan, Taiwan, Province of ChinaShow on map |
| Degree of Recognition | International |