Developmental changes in abundance of the VSPβ protein following nuclear transformation of maize with the Soybean vspβ cDNA

Abstract

Background: Developing 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.

A vegetative storage protein improves drought tolerance in maize

“…Expression of a dicot VSP, soybean VSPβ, in maize under the control of the p ZmUbi‐intron promoter resulted in its accumulation to a level of 0.5% of the total leaf protein in the primary transgenic plants. In the following generation, the expressed protein accumulated only to a level of 0.03% even though mRNA was present in the cells (Grando et al ., 2005). Translation efficiency of a nonmaize gene was apparently the cause for low‐level expression of the soybean VSP.…”

“…When the terminal sink for nitrogen storage is limiting in annual crops like soybean, for example, upon pod removal, VSPs take up the role of nitrogen storage reserves in the leaves (Bunker et al ., 1995; Dewald and Mason, 1992; Staswick, 1994). The occurrence of VSPs in grasses, the most widely cultivated group of crop plants globally, however, has not thus far been established (Grando et al ., 2005).…”