title: Gene expression activity and pathway selection for sucrose metabolism in developing storage root of sweet potato.
abstract: Development of sweet potato (Ipomoea batatas) storage root coincides with starch accumulation made using cleaved products of imported photoassimilate sucrose. The genes and pathways are predominantly active for sucrose metabolism in developing storage root were unknown. In this study, we used both an expressed sequence tag (EST) approach and a reverse transcription-polymerase chain reaction (RT-PCR) approach to answer this question. Sucrose synthase (SuSy) was found to be significantly more frequent in storage root ESTs than in fibrous root ESTs. SuSy was the most abundant carbohydrate-metabolism gene in the storage-root ESTs. RT-PCR results confirmed this by showing that invertase was active in fibrous roots but rapidly decreased to an undetectable level during storage root development while SuSy became predominant. Invertase expression was also detectable in young immature storage root and shoot tips, suggesting an involvement in cell formation. SuSy expression pattern showed considerable similarity to that of ADP-glucose pyrophosphorylase, an essential enzyme for starch synthesis. The results indicated that (i). SuSy was the most actively expressed enzyme in sucrose metabolism in developing storage root and was correlated with sink strength, and (ii). whereas invertase was active at cell formation stages, SuSy pathway was predominant for sucrose cleavage related to starch-accumulation.
authors.affiliation: Potato Research Centre, Agriculture and Agri-Food Canada, 850 Lincoln Road, PO Box 20280, Fredericton, NB, E3B 4Z7 Canada. lixq@agr.gc.ca
authors.forename: Xiu-Qing
authors.initials: XQ
authors.lastname: Li
authors.forename: Dapeng
authors.initials: D
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D018745:Genome, Plant; D015698:Genomic Library; D051599:Glucose-1-Phosphate Adenylyltransferase; D005964:Glucosyltransferases / Q000235:genetics; D006026:Glycoside Hydrolases / Q000235:genetics; D027741:Ipomoea / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis*; D013395:Sucrose / Q000378:metabolism*; D043324:beta-Fructofuranosidase
chemical_list: D018076:DNA, Complementary; D012333:RNA, Messenger; D013395:Sucrose; D013213:Starch; D005964:Glucosyltransferases; C022699:sucrose synthase; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase