Developmental and Light Regulation of Desacetoxyvindoline
4-Hydroxylase in Catharanthus roseus (L.) G. Don.1
Evidence of a Multilevel Regulatory Mechanism
Felipe A. Vazquez-Flota2 and
Vincenzo De Luca*
Institut de Recherche en Biologie Végétale,
Département de Sciences Biologiques, Université de
Montréal, 4101 Rue Sherbrooke est, Montréal,
Québec, Canada H1X 2B2
The
expression of desacetoxyvindoline 4-hydroxylase (D4H), which catalyzes
the second to the last reaction in vindoline biosynthesis in
Catharanthus roseus, appears to be under complex,
multilevel developmental and light regulation. Developmental studies
with etiolated and light-treated seedlings suggested that although light had variable effects on the levels of d4h
transcripts, those of D4H protein and enzyme activity could be
increased, depending on seedling development, up to 9- and 8-fold,
respectively, compared with etiolated seedlings. However, light
treatment of etiolated seedlings could stop and reverse the decline of
d4h transcripts at later stages of seedling development.
Repeated exposure of seedlings to light was also required to maintain
the full spectrum of enzyme activity observed during seedling
development. Further studies showed that a photoreversible phytochrome
appeared to be involved in the activation of D4H, since red-light
treatment of etiolated seedlings increased the detectable levels of
d4h transcripts, D4H protein, and D4H enzyme activity,
whereas far-red-light treatment completely reversed this process.
Additional studies also confirmed that different major isoforms of D4H
protein exist in etiolated (isoelectric point, 4.7) and light-grown
(isoelectric point, 4.6) seedlings, suggesting that a component of the
light-mediated activation of D4H may involve an undetermined
posttranslational modification. The biological reasons for this complex
control of vindoline biosynthesis may be related to the need to produce structures that could sequester away from cellular activities the
cytotoxic vinblastine and vincristine dimers that are derived partially
from vindoline.
1
This work was supported by the Natural Sciences
and Engineering Research Council of Canada and Le Fond pour la
Formation de Chercheurs et l'Aide à la Recherche.
2
F.A.V.-F. was supported by scholarships from the
National Council for Science and Technology (Mexico) and from Les
Bourses d'Excellence de la Faculté des Études
Supérieurs de l'Université de Montréal.
*
Corresponding author; e-mail delucavi{at}ere.umontreal.ca; fax
1-514-872-9406.
Plant Physiol. (1998) 117: 1351-1361
Copyright Clearance Center: 0032-0889/98/117//11
© 1998 American Society of Plant Physiologists
