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Published on April 3, 2009; 10.1104/pp.109.137042

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Received February 17, 2009
Accepted March 27, 2009

Timing and biosynthetic potential for carotenoid accumulation in genetically diverse germplasm of maize

Ratnakar Vallabhaneni and Eleanore T. Wurtzel *

Department of Biological Sciences, Lehman College, The City University of New York, 250 Bedford Park Blvd. West, Bronx, NY 10468; The Graduate School and University Center-CUNY, 365 Fifth Ave., New York, NY 10016-4309

* Corresponding author; email: wurtzel{at}lehman.cuny.edu.

Enhancement of the carotenoid biosynthetic pathway in food crops benefits human health and adds commercial value of natural food colorants. However, predictable metabolic engineering or breeding is limited by the incomplete understanding of endogenous pathway regulation, including rate-controlling steps and timing of expression in carotenogenic tissues. The Grass family (Poaceae) contains the major crop staples, including maize, wheat, rice, sorghum, and millets. Maize carotenogenesis was investigated using a novel approach to discover genes encoding limiting biosynthetic steps in the nutritionally targeted seed endosperm. A combination of bioinformatics and cloning were first used to identify and map gene families encoding enzymes in maize and other grasses. These enzymes represented upstream pathways for IPP and GGPP synthesis and the downstream carotenoid biosynthetic pathway, including conversion to ABA. A maize germplasm collection was used for statistical testing of correlation between carotenoid content and candidate gene transcript levels. Multiple pathway bottlenecks for isoprenoid biosynthesis and carotenoid biosynthesis were discovered in specific temporal windows of endosperm development. Transcript levels of paralogs encoding isoprenoid IPP and GGPP-producing enzymes, DXS3, DXR, HDR, and GGPPS1, were found to positively correlate with endosperm carotenoid content. For carotenoid pathway enzymes, transcript levels for CrtISO inversely correlated with seed carotenoid content, as compared to positive correlation of PSY1 transcripts. Since ZEP depletes the carotenoid pool in subsequent conversion to ABA, ZEP transcripts were examined. Carotenoid accumulation was found to be inversely associated with ZEP1 and ZEP2 transcript levels. Extension of the maize results using phylogenetic analysis identified orthologs in other Grass species that may serve as potential metabolic engineering targets.




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R. Vallabhaneni, C. E. Gallagher, N. Licciardello, A. J. Cuttriss, R. F. Quinlan, and E. T. Wurtzel
Metabolite Sorting of a Germplasm Collection Reveals the Hydroxylase3 Locus as a New Target for Maize Provitamin A Biofortification
Plant Physiology, November 1, 2009; 151(3): 1635 - 1645.
[Abstract] [Full Text] [PDF]


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