Multiple isoforms of starch branching enzyme-I in wheat: lack of the major SBE-I isoform does not alter starch phenotype

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doi:10.1071/FP03193

Multiple isoforms of starch branching enzyme-I in wheat: lack of the major SBE-I isoform does not alter starch phenotype

Ahmed Regina ^A ^B, Behjat Kosar-Hashemi ^A, Zhongyi Li ^A, Lynette Rampling ^A, Mark Cmiel ^A, Maria C. Gianibelli ^A, Christine Konik-Rose ^A, Oscar Larroque ^A, Sadequr Rahman ^A, Matthew K. Morell ^A

^A CSIRO Division of Plant Industry, PO Box 1600, Canberra, ACT 2601, Australia.
^B Corresponding author; email: regina.regina@csiro.au





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Functional Plant Biology 31(6) 591–601 http://dx.doi.org/10.1071/FP03193
Submitted: 22 October 2003 Accepted: 17 March 2004 Published online: 23 June 2004

Abstract

The role of starch branching enzyme-I (SBE-I) in determining starch structure in the endosperm has been investigated. Null mutations of SBE-I at the A, B and D genomes of wheat were identified in Australian wheat varieties by immunoblotting. By combining individual null mutations at the B and D genomes through hybridisation, a double-null mutant wheat, which lacks the B and D isoforms of SBE-I, was developed. Wheat mutants lacking all the three isoforms of SBE-I were generated from a doubled haploid progeny of a cross between the BD double-null mutant line and a Chinese Spring (CS) deletion line lacking the A genome isoform. Comparison of starch from this mutant wheat to that from wild type revealed no substantial alteration in any of the structural or functional properties analysed. Further analysis of this triple-null mutant line revealed the presence of another residual peak of SBE-I activity, referred to as SBE-I^r, in wheat endosperm representing < 3% of the activity of SBE-I in wild type endosperm.

Keywords: branching enzymes, null mutant, isoforms, starch, wheat.