Abstract
BackgroundGlucose-6-phosphate is imported into the amyloplast of potato tubers and thought to constitute the precursor for starch synthesis in potato tubers. However, recently it was shown that glucose-1-phosphate can also be imported into the amyloplast and incorporated into starch via an ATP independent mechanism under special conditions. Nonetheless, glucose-6-phosphate is believed to be the quantitatively important precursor for starch synthesis in potato.Principal FindingPotato tubers of the high yielding cv Kuras had low gene expression of plastidial phophoglucomutase (PGM) and normal levels of transcripts for other enzymes involved in starch metabolism in comparison with medium and low yielding cultivars as determined by DeepSAGE transcriptome profiling. The decrease in PGM activity in Kuras was confirmed by measuring the enzyme activity from potato tuber extracts. Contrary to expectations, this combination lead to a higher level of intracellular glucose-1-phosphate (G1P) in Kuras suggesting that G1P is directly imported into plastids and can be quantitatively important for starch synthesis under normal conditions in high yielding cultivars.SignificanceThis could open entirely new possibilities for metabolic engineering of the starch metabolism in potato via the so far uncharacterized G1P transporter. The perspectives are to increase yield and space efficiency of this important crop. In the light of the increasing demands imposed on agriculture to support a growing global population this presents an exciting new possibility.
Highlights
Potato (Solanum tuberosum) is the fourth most important crop in the world and belongs to the Solanaceae family together with other important crops as tomato, pepper and tobacco
In this study we show that differences in yield of different potato cultivars are reflected in specific, consistent and interpretable differences in gene expression in the starch metabolism, most notable plastidial and cytosolic PGM, which can be confirmed by measuring sucrose and hexose phosphate concentrations and the enzymatic PGM activity causing predictable differences in intracellular G1P and G6P levels
By measuring the concentrations of cellular G1P and G6P we found that Kuras contains an elevated ratio of G1P/G6P compared to Jutlandia and Desiree at week 12, 15 and 21
Summary
Potato (Solanum tuberosum) is the fourth most important crop in the world and belongs to the Solanaceae family together with other important crops as tomato, pepper and tobacco. Glucose-6-phosphate is believed to be the quantitatively important precursor for starch synthesis in potato. Principal Finding: Potato tubers of the high yielding cv Kuras had low gene expression of plastidial phophoglucomutase (PGM) and normal levels of transcripts for other enzymes involved in starch metabolism in comparison with medium and low yielding cultivars as determined by DeepSAGE transcriptome profiling. The decrease in PGM activity in Kuras was confirmed by measuring the enzyme activity from potato tuber extracts. Contrary to expectations, this combination lead to a higher level of intracellular glucose-1-phosphate (G1P) in Kuras suggesting that G1P is directly imported into plastids and can be quantitatively important for starch synthesis under normal conditions in high yielding cultivars
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