Regulation and activation of phytoene synthase, a key enzyme in carotenoid biosynthesis, during photomorphogenesis |
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Authors: | Ralf Welsch Peter Beyer Philippe Hugueney Hans Kleinig Johannes von Lintig |
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Institution: | Universit?t Freiburg, Center for Applied Biosciences, Sch?nzlestr. 1, 79104 Freiburg, Germany, DE
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Abstract: | During photomorphogenesis in higher plants, a coordinated increase occurs in the chlorophyll and carotenoid contents. The
carotenoid level is under phytochrome control, as reflected by the light regulation of the mRNA level of phytoene synthase
(PSY), the first enzyme in the carotenoid biosynthetic pathway. We investigated PSY protein levels, enzymatic activity and
topological localization during photomorphogenesis. The results revealed that PSY protein levels and enzymatic activity increase
during de-etiolation and that the enzyme is localized at thylakoid membranes in mature chloroplasts. However, under certain
light conditions (e.g., far-red light) the increases in PSY mRNA and protein levels are not accompanied by an increase in
enzymatic activity. Under those conditions, PSY is localized in the prolamellar body fraction in a mostly enzymatically inactive
form. Subsequent illumination of dark-grown and/or in far-red light grown seedlings with white light causes the decay of these
structures and a topological relocalization of PSY to developing thylakoids which results in its enzymatic activation. This
light-dependent mechanism of enzymatic activation of PSY in carotenoid biosynthesis shares common features with the regulation
of the NADPH:protochlorophyllide oxidoreductase, the first light-regulated enzyme in chlorophyll biosynthesis. The mechanism
of regulation described here may contribute to ensuring a spatially and temporally coordinated increase in both carotenoid
and chlorophyll contents.
Received: 14 February 2000 / Accepted: 15 March 2000 |
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Keywords: | : Chloroplast – Photomorphogenesis – Phytoene synthase – Prolamellar body – Sinapis (phytoene synthase) – Thylakoid |
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