Discrete forms of amylose are synthesized by isoforms of GBSSI in pea.
Amyloses with distinct molecular masses are found in the starch of pea embryos compared with the starch of pea leaves. In pea embryos, a granule-bound starch synthase protein (GBSSIa) is required for the synthesis of a significant portion of the amylose. However, this protein seems to be insignificant in the synthesis of amylose in pea leaves. cDNA clones encoding a second isoform of GBSSI, GBSSIb, have been isolated from pea leaves. Comparison of GBSSIa and GBSSIb activities shows them to have distinct properties. These differences have been confirmed by the expression of GBSSIa and GBSSIb in the amylose-free mutant of potato. GBSSIa and GBSSIb make distinct forms of amylose that differ in their molecular mass. These differences in product specificity, coupled with differences in the tissues in which GBSSIa and GBSSIb are most active, explain the distinct forms of amylose found in different tissues of pea. The shorter form of amylose formed by GBSSIa confers less susceptibility to the retrogradation of starch pastes than the amylose formed by GBSSIb. The product specificity of GBSSIa could provide beneficial attributes to starches for food and nonfood uses.
Edwards
Anne
A
John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom.
Vincken
Jean-Paul
JP
Suurs
Luc C J M
LC
Visser
Richard G F
RG
Zeeman
Sam
S
Smith
Alison
A
Martin
Cathie
C
D000595:Amino Acid Sequence; D000687:Amylopectin / Q000378:metabolism; D000688:Amylose / Q000032:analysis / Q000096:biosynthesis*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D018532:Pisum sativum / Q000201:enzymology* / Q000235:genetics; D010802:Phylogeny; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000096:biosynthesis; D030821:Plants, Genetically Modified; D012639:Seeds / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D011198:Solanum tuberosum / Q000235:genetics; D013213:Starch / Q000378:metabolism; D013214:Starch Synthase / Q000235:genetics / Q000378:metabolism*
D018076:DNA, Complementary; D007527:Isoenzymes; D010940:Plant Proteins; D013213:Starch; D000688:Amylose; D000687:Amylopectin; C434607:granule-bound starch synthase I; D013214:Starch Synthase