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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Maize Phytoene Synthase Gene Family: Overlapping Roles for Carotenogenesis in Endosperm, Photomorphogenesis, and Thermal Stress Tolerance^{1,[C],[W],[OA]}

Department of Biological Sciences, Lehman College, The City University of New York, Bronx, New York 10468 (F.L., R.V., J.Y., E.T.W.); Graduate School and University Center, The City University of New York, New York, New York 10016–4309 (F.L., R.V., J.Y., E.T.W.); and Department of Crop Sciences, University of Illinois, Urbana, Illinois 61801 (T.R.)

Carotenoids are essential for photosynthesis and photoprotection; they also serve as precursors to signaling molecules that influence plant development and biotic/abiotic stress responses. With potential to improve plant yield and nutritional quality, carotenoids are targets for metabolic breeding/engineering, particularly in the Poaceae (grass family), which includes the major food crops. Depending on genetic background, maize (Zea mays) endosperm carotenoid content varies, and therefore breeding-enhanced carotenoid levels have been of ongoing interest. The first committed step in the plastid-localized biosynthetic pathway is mediated by the nuclear-encoded phytoene synthase (PSY). The gene family in maize and other grasses contains three paralogs with specialized roles that are not well understood. Maize endosperm carotenoid accumulation requires PSY1 expression. A maize antibody was used to localize PSY1 to amyloplast envelope membranes and to determine PSY1 accumulation in relation to carotenoid accumulation in developing endosperm. To test when and if PSY transcript levels correlated with carotenoid content, advantage was taken of a maize germplasm diversity collection that exhibits genetic and chemical diversity. Total carotenoid content showed statistically significant correlation with endosperm transcript levels at 20 d after pollination for PSY1 but not PSY2 or PSY3. Timing of PSY1 transcript abundance, previously unknown, provides critical information for choosing breeding alleles or properly controlling introduced transgenes. PSY1 was unexpectedly found to have an additional role in photosynthetic tissue, where it was required for carotenogenesis in the dark and for heat stress tolerance. Leaf carotenogenesis was shown to require phytochrome-dependent and phytochrome-independent photoregulation of PSY2 plus nonphotoregulated PSY1 expression.

² Present address: Human Genetics, Fox Chase Cancer Center, 333 Cottman Ave., Philadelphia, PA 19111.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Eleanore T. Wurtzel (wurtzel{at}lehman.cuny.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.122119

^* Corresponding author; e-mail wurtzel{at}lehman.cuny.edu.

Received April 30, 2008; accepted May 20, 2008; published May 28, 2008.

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