Annals of Botany

Light and leaves – periwinkle proves DAT’s the way to do it

It is estimated that even in modern western medicine, 25 % of prescribed drugs are derived from plants. Admittedly over half of these are now manufactured synthetically but that still leaves a large number that are extracted from plants. Although many of these pharmaceuticals may be produced in cell cultures, others are only synthesized in specific types of cell. One example is the monoterpene-indole alkaloid (MIA), vindoline in Catharanthus roseus, as discussed by Campos-Tamayo et al. (Yucatan, Mexico; pp. 409– 415). Catharanthus roseus produces over 100 MIAs but only vindoline requires both light and the specialized cell organization of the aerial parts of the plant. Both these regulatory factors act via the activity of the last enzyme in the pathway, deacetylvindoline acetyl CoA acetyltransferase (DAT). To study the effects of both light and morphogenesis, the authors exposed shoot cultures to continuous light or to a 16-h photoperiod, monitoring the formation of new plantlets and the synthesis of vindoline over a 36-d period. Here we focus on the photoperiod experiments. Plantlet formation occurred in waves and increases in vindoline accumulation were correlated with these waves, as were peaks of DAT activity. Enzymes acting earlier in the MIA pathway did not show this correlation. However, peaks of DAT activity were not associated with peaks in transcription of the dat gene. This suggests that the changes in enzyme activity were at least in part mediated posttranscriptionally. Further, in these shoot cultures, vindoline synthesis is independent of the ORCA3 transcription factor, involved in the induction of MIAs by jasmonate. Finally, the authors used plant hormones to disrupt the genesis of new plantlets, leading to the formation of ‘de-differentiated’ cultures. Vindoline accumulation ceased and the amount in the cultures fell to zero within 14 d, as did the activity of DAT. These data thus emphasize the linkage between morphogenesis and the synthesis of a specific secondary metabolite.