Comparison of starch-branching enzyme genes reveals evolutionary relationships among isoforms. Characterization of a gene for starch-branching enzyme IIa from the wheat genome donor Aegilops tauschii.
Genes and cDNAs for starch-branching enzyme II (SBEII) have been isolated from libraries constructed from Aegilops tauschii and wheat (Triticum aestivum) endosperm, respectively. One class of genes has been termed wSBEII-DA1 and encodes the N terminus reported for an SBEII from wheat endosperm. On the basis of phylogenetic comparisons with other branching enzyme sequences, wSBEII-DA1 is considered to be a member of the SBEIIa class. The wSBEII-DA1 gene consists of 22 exons with exons 4 to 21 being identical in length to the maize (Zea mays) SBEIIb gene, and the gene is located in the proximal region of the long arm of chromosome 2 at a locus designated sbe2a. RNA encoding SBEIIa can be detected in the endosperm from 6 d after flowering and is at its maximum level from 15 to 18 d after anthesis. Use of antibodies specific for SBEIIa demonstrated that this protein was present in both the soluble and granule bound fractions in developing wheat endosperm. We also report a cDNA sequence for SBEIIa that could arise by variant transcription/splicing. A second gene, termed wSBEII-DB1, was isolated and encodes an SBEII, which shows greater sequence identity with SBEIIb-type sequences than with SBEIIa-type sequences. Comparisons of SBEII gene structures among wheat, maize, and Arabidopsis indicate the lineage of the SBEII genes.
Commonwealth Scientific and Industrial Research Organization Plant Industry, P.O. Box 1600, Australian Capital Territory 2601, Australia. s.rahman@pi.csiro.au
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S
Rahman
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A
Regina
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Z
Li
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Mukai
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M
Yamamoto
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Kosar-Hashemi
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Abrahams
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Morell
D015061:1,4-alpha-Glucan Branching Enzyme / Q000737:chemistry / Q000235:genetics*; D000595:Amino Acid Sequence; D018076:DNA, Complementary; D019143:Evolution, Molecular; D018745:Genome, Plant; D017404:In Situ Hybridization, Fluorescence; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014908:Triticum / Q000201:enzymology / Q000235:genetics*
D018076:DNA, Complementary; D007527:Isoenzymes; D015061:1,4-alpha-Glucan Branching Enzyme; C112590:starch-branching enzyme II