Starch branching enzyme IIb in wheat is expressed at low levels in the endosperm compared to other cereals and encoded at a non-syntenic locus.
Studies of maize starch branching enzyme mutants suggest that the amylose extender high amylose starch phenotype is a consequence of the lack of expression of the predominant starch branching enzyme II isoform expressed in the endosperm, SBEIIb. However, in wheat, the ratio of SBEIIb and SBEIIa expression are inversely related to the expression levels observed in maize and rice. Analysis of RNA at 15 days post anthesis suggests that there are about 4-fold more RNA for SBE IIa than for SBE IIb. The genes for SBE IIa and SBE IIb from wheat are distinguished in the size of the first three exons, allowing isoform-specific antibodies to be produced. These antibodies were used to demonstrate that in the soluble fraction, the amount of SBE IIa protein is two to three fold higher than SBIIb, whereas in the starch granule, there is two to three fold more SBE IIb protein amount than SBE IIa. In a further difference to maize and rice, the genes for SBE IIa and SBE IIb are both located on the long arm of chromosome 2 in wheat, in a position not expected from rice-maize-wheat synteny.
Regina
Ahmed
A
Commonwealth Scientific and Industrial Research Organisation, Plant Industry, P.O. Box 1600, Australian Capital Territory, 2601, Australia.
Kosar-Hashemi
Behjat
B
Li
Zhongyi
Z
Pedler
Andrew
A
Mukai
Yasuhiko
Y
Yamamoto
Maki
M
Gale
Kevin
K
Sharp
Peter J
PJ
Morell
Matthew K
MK
Rahman
Sadequr
S
D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002874:Chromosome Mapping; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D002523:Edible Grain / Q000201:enzymology / Q000235:genetics; D015870:Gene Expression; D017343:Genes, Plant; D017404:In Situ Hybridization, Fluorescence; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014908:Triticum / Q000201:enzymology* / Q000235:genetics*
D018076:DNA, Complementary; D018744:DNA, Plant; D007527:Isoenzymes; D012333:RNA, Messenger; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D015061:1,4-alpha-Glucan Branching Enzyme