Abstract
BackgroundDeveloping monocots that accumulate more vegetative tissue protein is one strategy for improving nitrogen-sequestration and nutritive value of forage and silage crops. In soybeans (a dicotyledonous legume), the vspA and B genes encode subunits of a dimeric vegetative storage protein that plays an important role in nitrogen storage in vegetative tissues. Similar genes are found in monocots; however, they do not accumulate in leaves as storage proteins, and the ability of monocot leaves to support accumulation of an ectopically expressed soybean VSP is in question. To test this, transgenic maize (Zea Mays L. Hi-II hybrid) lines were created expressing soybean vspB from a maize ubiquitin Ubi-1 promoter.ResultsFrom 81 bombardments, 101 plants were regenerated, and plants from five independent lines produced vspB transcripts and VSPβ polypeptides. In leaves from seven-week-old plants (prior to flowering), VSPβ accumulated to 0.5% of the soluble leaf protein in primary transgenic plants (R0), but to only 0.03% in R1 plants. During seed-filling (silage-stage) in R1 plants, the VSPβ protein was no longer detected in leaves and stems despite continued presence of the vspB RNA. The RNA transcripts for this peptide either became less efficiently translated, or the VSPβ protein became unstable during seed-fill.ConclusionDevelopmental differences in the accumulation of soybean VSPβ when transgenically expressed in maize show that despite no changes in the vspB transcript level, VSPβ protein that is readily detected in leaves of preflowering plants, becomes undetectable as seeds begin to develop.
Highlights
Developing monocots that accumulate more vegetative tissue protein is one strategy for improving nitrogen-sequestration and nutritive value of forage and silage crops
Development of primary (R0) transgenic maize expressing vspB Out of 101 plants, twenty, belonging to five independent lines (71-1, 45-1, 45-3, 44-1, and 4-1) were shown by Southern blot analysis to contain a 1.5 kb hybridizing band corresponding to the intact bar gene (Fig. 1)
The vspB gene was successfully introduced into R0 regenerated maize and transferred to the R1 progeny, of which vspB transcript and VSPβ protein were detected and studied
Summary
Developing monocots that accumulate more vegetative tissue protein is one strategy for improving nitrogen-sequestration and nutritive value of forage and silage crops. BMC Plant Biology 2005, 5:3 http://www.biomedcentral.com/1471-2229/5/3 protein quality and content through expression of a storage protein not found in grass vegetative tissue. Genes encoding seed storage proteins of various plant species have been transgenically expressed to test for improvement of nutritional quality. For nuclear-targeted genes, accumulation of these seed storage proteins in vegetative tissue of transgenic plants was either undetectable or very low. These included pea vicilin [2,3], soybean conglycinin [4], sunflower seed agglutinin [5,6], and phaseolin [7]. The instability of seed proteins in nonseed tissues of transgenic plants was frequently attributed to protein targeting to protease-rich vacuoles in the vegetative cells, and subsequent degradation [5,7,8]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call