Improving SNF and replacing inorganic fertilizers are both important goals in establishing sustainable and more energy-efficient farming. SNF already occurs on a large scale "biological nitrogen” contributes about 5 Tg N/yr to American agriculture, a quarter of the nitrogen needed. SNF describes mutualistic interactions where nitrogen-fixing bacteria provide fixed nitrogen to their plant hosts, freeing them from the need for nitrogen fertilizers. How to alter this addiction is not obvious, but the best chance to secure more » substantial and sustainable amounts of future N might be through symbiotic nitrogen fixation (SNF). Manufacturing fertilizer is essential-without it there would only be enough combined nitrogen to feed ~3 billion of the world’s ~7 billion people. Making N fertilizers leverages methane’s energy content by enabling additional energy to be captured into food and fiber through increased photosynthesis. Nitrogen fertilizer production uses ~4% of the world’s natural gas. Atmospheric dinitrogen is too stable to be used directly by plants, so plants need other chemical forms of nitrogen. One of the most critical uses of carbon fuels is in generating nitrogen fertilizer. (PNNL), Richland, WA (United States) Sponsoring Org.: USDOE National Science Foundation (NSF) OSTI Identifier: 1714364 Report Number(s): PNNL-SA-155876 Journal ID: ISSN 0032-0781 Grant/Contract Number: AC05-76RL01830 0818182 Resource Type: Journal Article: Accepted Manuscript Journal Name: Plant and Cell Physiology Additional Journal Information: Journal Volume: 61 Journal Issue: 10 Journal ID: ISSN 0032-0781 Publisher: Japanese Society of Plant Physiologists Country of Publication: United States Language: English Subject: 59 BASIC BIOLOGICAL SCIENCES Ca2+-dependent contractility forisome phloem SEO protein SEOR protein sieve = , Publication Date: Thu Jul 16 00:00: Research Org.: Pacific Northwest National Lab. Washington State Univ., Pullman, WA (United States) Pacific Northwest National Lab.Lumencor Inc, Beaverton, OR (United States).Washington State Univ., Pullman, WA (United States).To conclude, this study defines a promising path to the elucidation of the so-far elusive molecular mechanisms of forisome assembly and Ca 2+-dependent contractility. Finally, we observed a previously unknown surface striation in native forisomes and in recombinant forisome-like bodies more » that could serve as an indicator of successful forisome assembly. The phenotypes observed further suggested that Ca 2+-controlled and pH-inducible swelling effects in forisome-like bodies proceeded by different yet interacting mechanisms. We identified three aspartate residues critical for Ca 2+ responsiveness and two more that were required for forisome-like bodies to assemble. We exchanged identified candidate residues by directed mutagenesis of the Medicago truncatula SEO1 gene, expressed the mutated genes in yeast ( Saccharomyces cerevisiae) and studied the structural and functional phenotypes of the forisome-like bodies that formed in the transgenic cells. SEOR proteins resemble SEO proteins closely but lack any Ca 2+ responsiveness. Here we selected amino acids potentially responsible for forisome-specific functions by analyzing SEO protein sequences in comparison to those of the widely distributed SEO-related (SEOR), or SEOR proteins. The assembly of forisomes from sieve element occlusion (SEO) protein monomers in developing sieve elements and the mechanism(s) of Ca 2+-dependent forisome contractility are poorly understood because the amino acid sequences of SEO proteins lack conventional protein–protein interaction and Ca 2+-binding motifs. Forisomes contribute to the regulation of phloem transport due to their unique Ca 2+-controlled, reversible swelling. Forisomes are protein bodies known exclusively from sieve elements of legumes.
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