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Contributed by Joachim Messing, September 1, 2017 (sent for review August 22, 2017; reviewed by L. Curtis Hannah and Ronald L. Phillips)
Significance
Poultry feed is usually prepared as a corn–soybean mixture. Because the only essential sulfur amino acid missing in this mixture is methionine, it is chemically synthesized and added separately, increasing the cost of major food supply. It appears to be difficult to circumvent the regulatory aspects of sulfur metabolism, which is controlled at many levels, without damage to plant growth. By using tissue-specific promoters to express a bacterial enzyme that increases the efficiency of assimilative sulfate reduction, seed methionine accumulation can be increased without the concomitant accumulation of toxic metabolites. We show that even in maize inbred lines with repressed seed methionine levels, sink strength can be increased to the benefit of feed consumption efficiency in chicks.
Abstract
Sulfur assimilation may limit the pool of methionine and cysteine available for incorporation into zeins, the major seed storage proteins in maize. This hypothesis was tested by producing transgenic maize with deregulated sulfate reduction capacity achieved through leaf-specific expression of the Escherichia coli enzyme 3′-phosphoadenosine-5′-phosphosulfate reductase (EcPAPR) that resulted in higher methionine accumulation in seeds. The transgenic kernels have higher expression of the methionine-rich 10-kDa δ-zein and total protein sulfur without reduction of other zeins. This overall increase in the expression of the S-rich zeins describes a facet of regulation of these proteins under enhanced sulfur assimilation. Transgenic line PE5 accumulates 57.6% more kernel methionine than the high-methionine inbred line B101. In feeding trials with chicks, PE5 maize promotes significant weight gain compared with nontransgenic kernels. Therefore, increased source strength can improve the nutritional value of maize without apparent yield loss and may significantly reduce the cost of feed supplementation.
Footnotes
- ↵1To whom correspondence should be addressed. Email: messing{at}waksman.rutgers.edu.
Author contributions: J.P., T.L., and J.M. designed research; J.P. and X.X. performed research; J.P., T.L., and J.M. analyzed data; and J.P., T.L., and J.M. wrote the paper.
Reviewers: L.C.H., University of Florida; and R.L.P., University of Minnesota.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1714805114/-/DCSupplemental.
Amino acids for food and feed
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