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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Quantitative Proteomics of Seed Filling in Castor: Comparison with Soybean and Rapeseed Reveals Differences between Photosynthetic and Nonphotosynthetic Seed Metabolism^{1,[C],[W],[OA]}

Interdisciplinary Plant Group and Department of Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211

Seed maturation or seed filling is a phase of development that plays a major role in the storage reserve composition of a seed. In many plant seeds photosynthesis plays a major role in this process, although oilseeds, such as castor (Ricinus communis), are capable of accumulating oil without the benefit of photophosphorylation to augment energy demands. To characterize seed filling in castor, a systematic quantitative proteomics study was performed. Two-dimensional gel electrophoresis was used to resolve and quantify Cy-dye-labeled proteins expressed at 2, 3, 4, 5, and 6 weeks after flowering in biological triplicate. Expression profiles for 660 protein spot groups were established, and of these, 522 proteins were confidently identified by liquid chromatography-tandem mass spectrometry by mining against the castor genome. Identified proteins were classified according to function, and the most abundant groups of proteins were involved in protein destination and storage (34%), energy (19%), and metabolism (15%). Carbon assimilatory pathways in castor were compared with previous studies of photosynthetic oilseeds, soybean (Glycine max) and rapeseed (Brassica napus). These comparisons revealed differences in abundance and number of protein isoforms at numerous steps in glycolysis. One such difference was the number of enolase isoforms and their sum abundance; castor had approximately six times as many isoforms as soy and rapeseed. Furthermore, Rubisco was 11-fold less prominent in castor compared to rapeseed. These and other differences suggest some aspects of carbon flow, carbon recapture, as well as ATP and NADPH production in castor differs from photosynthetic oilseeds.

² Present address: Institute of Plant Genetics and Biotechnology, Slovak Academy of Sciences, 95007 Nitra, Slovak Republic.

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: Jay J. Thelen (thelenj{at}missouri.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.109.141622

^* Corresponding author; e-mail houstonn{at}missouri.edu.

Received May 18, 2009; accepted August 11, 2009; published August 12, 2009.