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Seed oil and protein are important nutrient sources for human and livestock, and raw materials for various industrial products. Optimization of oil to protein ratio is highly desirable in agriculture and has therefore been the target of extensive breeding efforts. The partitioning of carbon between seed protein and oil is controlled, at least in part, by mechanisms that coordinate plant carbon, energy, and nitrogen metabolism. However, a precise understanding of these mechanisms still relies on identification and characterization of key molecular components. The Arabidopsis carbon partitioning 1 (cap1) mutant exhibits an increased seed protein to oil ratio and the corresponding gene encodes ATP-phosphoribosyl transferase 1 (ATP-PRT1), which is known to catalyze the first and committed step of histidine biosynthesis. Because histidine deficiency per se does not explain the elevation of seed protein content, a regulatory role of ATP-PRT1 and histidine is suggested by the mutant phenotype. It is hypothesized that histidine, a special amino acid that is linked to energy metabolism, acts as a nitrogen signal to regulate cellular pathways, and that ATP-PRT1 adjusts the flow of histidine biosynthesis according to carbon and energy status through the known allosteric mechanisms. Consistent with this hypothesis, biochemical and molecular evidence indicate that multiple changes occur in concert in the cap1 mutant to cause reduction of carbon assimilation and seed oil accumulation, but increase of seed protein synthesis. Further investigation of ATP-PRT1' functions in regulating plant metabolism and storage could offer simple means of genetic engineering to optimize oil to protein ratio in crop seeds.
Shui Wang and Yun Lin1
Department of Crop Sciences
University of Illinois
1 Yun Lin