Aspartate Residues in a Forisome-Forming SEO Protein Are Critical for Protein Body Assembly and Ca2+ Responsiveness.

Autor: Liu Y; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA., Peters WS; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA., Froelich DR; Lumencor Inc, 14940 NW Greenbrier Parkway, Beaverton, OR 97006, USA., Howell AH; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA., Mooney S; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA., Evans JE; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA.; Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Blvd, Richland, WA 99354, USA., Hellmann HA; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA., Knoblauch M; School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164, USA.
Jazyk: angličtina
Zdroj: Plant & cell physiology [Plant Cell Physiol] 2020 Oct 01; Vol. 61 (10), pp. 1699-1710.
DOI: 10.1093/pcp/pcaa093
Abstrakt: Forisomes are protein bodies known exclusively from sieve elements of legumes. Forisomes contribute to the regulation of phloem transport due to their unique Ca2+-controlled, reversible swelling. The assembly of forisomes from sieve element occlusion (SEO) protein monomers in developing sieve elements and the mechanism(s) of Ca2+-dependent forisome contractility are poorly understood because the amino acid sequences of SEO proteins lack conventional protein-protein interaction and Ca2+-binding motifs. 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. SEOR proteins resemble SEO proteins closely but lack any Ca2+ responsiveness. 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. We identified three aspartate residues critical for Ca2+ responsiveness and two more that were required for forisome-like bodies to assemble. The phenotypes observed further suggested that Ca2+-controlled and pH-inducible swelling effects in forisome-like bodies proceeded by different yet interacting mechanisms. Finally, we observed a previously unknown surface striation in native forisomes and in recombinant forisome-like bodies that could serve as an indicator of successful forisome assembly. To conclude, this study defines a promising path to the elucidation of the so-far elusive molecular mechanisms of forisome assembly and Ca2+-dependent contractility.
(© The Author(s) 2020. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)
Databáze: MEDLINE
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