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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #156801
Title: DEVELOPMENTAL CHANGES IN ABUNDANCE OF THE VSPBETA PROTEIN FOLLOWING NUCLEAR TRANSFORMATION OF MAIZE WITH THE SOYBEAN VSPBETA CDNA.

Author
item GRANDO, MAGALI - UNIV. DE PASSO FUNDO, BR
item SMITH, REX - IFAS, UNIV. OF FL
item MOREIRA, CRISTINA - MARTIN COUNTY
item SCULLY, BRIAN - IFAS, UNIV. OF FL
item Shatters, Robert - Bob

Submitted to: Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2005
Publication Date: 3/2/2005
Citation: Grando, M.F., Smith, R., Moreira, C., Scully, B.T., Shatters, R.G. 2005. Developmental changes in abundance of the VSP-Beta protein following nuclear transformation of maize with the soybean VSP-Beta cDNA. Plant Biology. 5(3):1471-2229.

Interpretive Summary: Corn is a primary source of silage for cattle and dairy feed; however,the protein content of silage produced from corn is relatively low. As a result, corn silage must be supplemented with higher protein content feed (i.e. soybean meal) and this practice increases the total feed cost of milk production. Although legumes, like soybeans, produce vegetative plant tissue with much higher nitrogen levels than found in corn, soybean is not suitable for silage production. In this report, the gene from soybean that encodes the major vegetative tissue storage protein was expressed in corn to determine the fate of this protein when expressed in corn vegetative tissues. These corn plants accumulated the soybean storage protein in leaves and stems prior to seed development; however, after initiation of seed development, the soybean protein was no longer detectable in the vegetative tissues. Our data suggest that during seed development the soybean protein is degraded in the vegetative tissue perhaps to mobilize the nitrogen within this protein for support of seed development. Therefore, protein accumulation in the form of the soybean storage protein will not interfere with seed development by sequestering nitrogen that the seed requires to develop normally. In this study, the level of soybean storage protein accumulation in leaves of preflowering plants was too low to allow a significant change in overall plant protein content. However, if this gene can be expressed at higher levels in maize, our data indicate that the protein accumulated during the preflowering development of the corn plant, should be available to improve protein content of the seed as well as the whole plant silage quality.

Technical Abstract: Developing monocots that accumulate more vegetative tissue protein could improve nitrogen-sequestration and nutritive value of forage and silage crops. In soybeans, 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. From 81 bombardments, 101 plants were regenerated, and plants from five independent lines produced vspB transcripts and VSPB polypeptides. In leaves from seven-week-old plants (prior to flowering), VSPB accumulated to 0.6% 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 VSPB protein was no longer detected in leaves and stems despite continued presence of the vspB RNA. Therefore, the RNA transcripts for this peptide either become less efficiently translated, or the VSPB protein becomes unstable during seed-fill, suggesting that maize may be able to mobilize the soybean VSP to support seed development. Therefore VSP expression in maize is not competitive with seed development and thus may function as an efficient way of accumulating nitrogen during plant development to aid in subsequent seed production as well as improving forage/silage quality.