Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/1994
Publication Date: N/A
Citation: Interpretive Summary: Starch synthesis is a fundamental process in plant biology and is of particular concern to the agricultural community as it is the primary component in all the major food and feed crops such as potato, corn, wheat, rice, and barley. Because of the importance of starch we are interested in how starch synthesis is controlled, particularly in those parts of the plant which are harvested for food, feed or industrial uses. In this stud we have shown that the gene for a portion or subunit of a key enzyme in potato starch synthesis has a complex structure and that it exists in only one copy in the potato genome. This one gene is expressed in both leaf and tuber tissues unlike other plants such as corn and wheat which have tissue specific forms of this enzyme. This study has determined that the amount of this enzyme present in leaf and potato tubers is controlled differently in these two very different parts of the potato plant which in turn determines how much starch is being produced. These results have defined key point in how starch synthesis is controlled particularly in the potato tuber. This information has shown us and other scientists what to change in order to alter the amount of starch being produced. Changing the amount of starch has the potential for increasing yield and altering feed, food and industrial use characteristics in potato and other cereal crops to make better or different products.
Technical Abstract: ADPglucose pyrophosphorylase (AGP) catalyzes the key regulatory step in starch synthesis. To elucidate the molecular basis for the expression of the potato AGP during tuber development, the structure of the small subunit AGP (sACP) gene and its pattern of expression were examined. DNA sequence analysis revealed that the sAGP gene is over 5.5 kilobases long and has a complex structure including eight introns. Unlike the situation in other plants where tissue-specific sAGP are found, our Southern and Northern blot analysis indicated that the same sAGP gene is expressed in both tubers (non-photosynthetic tissue) and leaves (photosynthetic tissue). These data were supported by comparing sequences of isolated sAGP leaf cDNAs to the tuber cDNA sequence, by primer extension analysis of leaf and tuber poly(A)+RNAs, and by the spatial expression patterns of a B-glucuronidase reporter gene driven by the potato sAGP promoter in transgenic potato plants. Although the sAGP gene appears to be transcriptionally controlled in both developing tubers and in leaves, the relative level of leaf antigen was significantly lower than its level of transcript, indicating that sAGP expression in leaves is primarily regulated post-transcriptionally. The observed tissue type-dependent regulation of sAGP expression appears to control the extent of starch biosynthesis by regulating the levels of this enzyme and, thus, alleviate the need for tissue-specific forms of the sAGP in potato.