title: Differential expression and properties of starch branching enzyme isoforms in developing wheat endosperm.
abstract: Three forms of starch branching enzyme (BE) from developing hexaploid wheat (Triticum aestivum) endosperm have been partially purified and characterized. Immunological cross-reactivities indicate that two forms (WBE-IAD, 88 kD, and WBE-IB, 87 kD) are related to the maize BE I class and that WBE-II (88 kD) is related to maize BE II. Comparison of the N-terminal sequences from WBE-IAD and WBE-II with maize and rice BEs confirms these relationships. Evidence is presented from the analysis of nullisomic-tetrasomic wheat lines demonstrating that WBE-IB is located on chromosome 7B and that the WBE-IAD fraction contains polypeptides that are encoded on chromosomes 7A and 7D. The wheat endosperm BE classes are differentially expressed during endosperm development. WBE-II is expressed at a constant level throughout mid and late endosperm development. In contrast, WBE-IAD and WBE-IB are preferentially expressed in late endosperm development. Differences are also observed in the kinetic characteristics of the enzymes. The WBE-I isoforms have a 2- to 5-fold higher affinity for amylose than does WBE-II, and the WBE-I isoforms are activated up to 5-fold by phosphorylated intermediates and inorganic phosphate, whereas WBE-II is activated only 50%. The potential implications of this activation of BE I for starch biosynthesis are discussed.
authors.affiliation: Cooperative Research Centre for Plant Science, Canberra, Australia. morell@rsbs-central.anu.edu.au
authors.forename: M K
authors.initials: MK
authors.lastname: Morell
authors.forename: A
authors.initials: A
authors.lastname: Blennow
authors.forename: B
authors.initials: B
authors.lastname: Kosar-Hashemi
authors.forename: M S
authors.initials: MS
authors.lastname: Samuel
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007527:Isoenzymes / Q000235:genetics*; D007700:Kinetics; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D007527:Isoenzymes; D015061:1,4-alpha-Glucan Branching Enzyme