F. Takaiwa et al., HIGH-LEVEL ACCUMULATION OF SOYBEAN GLYCININ IN VACUOLE-DERIVED PROTEIN BODIES IN THE ENDOSPERM TISSUE OF TRANSGENIC TOBACCO SEED, PLANT SCI, 111(1), 1995, pp. 39-49
Soybean glycinin genes are expressed specifically in the cotyledon and
embryo of maturing soybean seed, from which the endosperm tissue is d
egenerated. To examine whether glycinin could be stably accumulated in
endosperm tissue, the glycinin cDNA was transcriptionally fused to an
endosperm-specific promoter of the rice storage protein glutelin gene
and then introduced into tobacco genome via Agrobacterium-mediated tr
ansformation. Consequently the glycinin gene was expressed in a seed-
and developmentally-specific manner in transgenic tobacco seeds. Glyci
nins were targeted to vacuole-derived protein bodies in the endosperm
tissue and highly accumulated in the matrix region of many transgenic
plants (1-4% of total seed proteins). Synthesized glycinin was process
ed into mature form, and assembled into a hexamer in a similar manner
as the glycinin in soybean seed, However, it was noteworthy that about
half of the synthesized glycinin was susceptible to limited degradati
on and that assembly into a hexamer was insufficient. Modified glycini
ns, in which 4 contiguous methionine residues were inserted at the var
iable regions corresponding to the C-terminal regions of the acidic an
d basic polypeptides, were also found to be accumulated similarly as i
n the normal glycinin. There was no apparent difference in the express
ion level, processing and targeting to protein bodies, or accumulation
level between normal and modified glycinins.