PLANT PHYSIOLOGY , Vol 109, Issue 3 777-786, Copyright © 1995 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
The Bean Seed Storage Protein [beta]-Phaseolin Is Synthesized, Processed, and Accumulated in the Vacuolar Type-II Protein Bodies of Transgenic Rice Endosperm
Z. Zheng, K. Sumi, K. Tanaka and N. Murai
Department of Plant Pathology and Crop Physiology, Louisiana State University (LSU), and LSU Agricultural Center, Baton Rouge, Louisiana 70803-1720 (Z.Z., N.M.)
The seed storage protein [beta]-phaseolin of the common bean (Phaseolus
vulgaris L.) was expressed in the endosperm of transgenic rice (Oryza
sativa L.) plants. The 5.1- or 1.8-kb promoter fragment of the rice seed
storage protein glutelin Gt1 gene was fused transcriptionally to either the
genomic or cDNA coding sequence of the [beta]-phaseolin gene. The highest
quantity of phaseolin estimated by enzyme-linked immunosorbent assay was
4.0% of the total endosperm protein in the transgenic rice seeds. The
phaseolin trait was segregated as a single dominant trait with a positive
gene dosage effect and was stably inherited through three successive
generations. Both phaseolin genomic and cDNA coding sequences were used to
synthesize four isoforms of mature phaseolin protein with apparent
molecular masses of 51, 48, 47, and 45 kD. Enzyme deglycosylation
experiments indicated that the 51-kD form contains high-mannose N-glycans;
the 48- and 47-kD forms have further modified N-glycans; and the 45-kD form
is a nonglycosylated protein. Immunolabeling studies using light and
electron microscopy demonstrated that phaseolin accumulates primarily in
the vacuolar type-II protein bodies located at the periphery of the
endosperm near the aleurone layer. We discuss the implications of these
results on nutritional improvement of rice grains.
