PLANT PHYSIOLOGY , Vol 110, Issue 2 355-363, Copyright © 1996 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Fructan Accumulation and Sucrose Metabolism in Transgenic Maize Endosperm Expressing a Bacillus amyloliquefaciens SacB Gene
P. G. Caimi, L. M. McCole, T. M. Klein and P. S. Kerr
Agricultural Products, E. I. DuPont de Nemours & Co., Wilmington, Delaware 19880-0402
Over 40,000 species of plants accumulate fructan, [beta]-2-1- and
[beta]-2-6-linked polymers of fructose as a storage reserve. Due to their
high fructose content, several commercial applications for fructans have
been proposed. However, plants that accumulate these polymers are not
agronomically suited for large-scale cultivation or processing. This study
describes the transformation of a Bacillus amyloliquefaciens SacB gene into
maize (Zea mays L.) callus by particle bombardment. Tissue-specific
expression and targeting of the SacB protein to endosperm vacuoles resulted
in stable accumulation of high-molecular-weight fructan in mature seeds.
Accumulation of fructan in the vacuole had no detectable effect on kernel
development or germination. Fructan levels were found to be approximately
9-fold higher in sh2 mutants compared to wild-type maize kernels. In
contrast to vacuole-targeted expression, starch synthesis and endosperm
development in mature seeds containing a cytosolically expressed SacB gene
were severely affected. The data demonstrate that hexose resulting from
cytosolic SacB activity was not utilized for starch synthesis. Transgenic
seeds containing a chimeric SacB gene provide further evidence that the
dominant pathway for starch synthesis in maize endosperm is through uridine
diphosphoglucose catalyzed by the enzyme sucrose synthase.
