Synthesis and protein body deposition of maize 15-kd zein in transgenic tobacco seeds

Abstract

The maize 15‐Kd zein structural gene was placed under the regulation of French bean β‐phaseolin gene flanking regions. Agrobacterium tumefaciens‐mediated transformation was used to insert the chimeric phaseolin–zein gene into the tobacco genome. Transgenic plants synthesized zein in a tissue‐specific manner during the latter half of seed development. Transcription of the chimeric gene was initiated in phaseolin‐derived sequences, and was terminated within the phaseolin gene 3′ flanking region. Both zein‐ and phaseolin‐derived polyadenylation signals were used in the processing of zein RNA in transgenic plant seeds. Zein accumulation, though subject to an 80‐fold variation among 19 plants tested, could reach as much as 1.6% of the total seed protein in several plants. In developing tobacco seeds, zein was correctly processed by the removal of a 20‐amino‐acid signal peptide. Electron microscope immunogold localization of the zein expressed in embryo and endosperm tissue indicates that the monocot protein accumulates in the crystalloid component of vacuolar protein bodies. The density of gold label over the protein bodies is several fold greater in the embryo than the endosperm. Zein is found in roots, hypocotyls and cotyledons of germinating transgenic tobacco seeds.

Accumulation of 15-Kilodalton Zein in Novel Protein Bodies in Transgenic Tobacco

“…Can the discrepancy between our results and those of Hoffman et al (1987) be attributed to differences in the nature of the promoter driving the 15-kD zein gene in transgenic tobacco? Although the two promoters do differ in their temporal and spatial patterns of expression, it is difficult to envision how that could determine the final destination of the protein.…”

“…It is interesting to note that Hoffman et al (1987) did not report the presence of the specialized ER-derived protein bodies in seeds of transgenic tobacco containing the 15-kD zein gene behind the j3-phaseolin gene promoter. The 15-kD zein protein in their system appeared to be localized in the crystalloid component of the storage vacuole.…”

“…In an earlier paper, Hoffman et al (1987) reported that, in transgenic tobacco in which the 15-kD zein gene is driven by the seed-specific /3-phaseolin gene promoter, the zein protein was found to accumulate in vacuolar protein bodies in mature seeds. To determine whether the same pattern would hold in our system with the 15-kD zein gene being driven by the constitutive 35S promoter, both immature ( Fig.…”

Coexpression of the maize delta-zein and beta-zein genes results in stable accumulation of delta-zein in endoplasmic reticulum-derived protein bodies formed by beta-zein.

“…It was shown previously that p-zein in transgenic tobacco seeds is not proteolytically digested during germination (Hoffman et al, 1987;Bagga et al, 1997). To determine whether 8-zein behaves in a similar manner, seeds from a 8-zein plant were allowed to germinate for different time periods (0 to 10 days), and the seeds/seedlings were harvested and their ethanol-soluble proteins extracted and analyzed by immunoblotting using the 8-zein antibodies (Figure 2).…”

GENOMIQUE ET PRODUCTION NON ALIMENTAIRE Acides gras d’intérêt industriel obtenus par génie génétique

“…Des résultats analogues ont été obtenus par d'autres laboratoires par l'expression de protéines recombinantes riches en acides aminés soufrés ; 15 kd zéine du maïs, albumine 2 S de la noix du Brésil, albumine du tournesol... [3][4][5].…”