title: GFP tagging of sieve element occlusion (SEO) proteins results in green fluorescent forisomes.
abstract: Forisomes are Ca(2+)-driven, ATP-independent contractile protein bodies that reversibly occlude sieve elements in faboid legumes. They apparently consist of at least three proteins; potential candidates have been described previously as 'FOR' proteins. We isolated three genes from Medicago truncatula that correspond to the putative forisome proteins and expressed their green fluorescent protein (GFP) fusion products in Vicia faba and Glycine max using the composite plant methodology. In both species, expression of any of the constructs resulted in homogenously fluorescent forisomes that formed sieve tube plugs upon stimulation; no GFP fluorescence occurred elsewhere. Isolated fluorescent forisomes reacted to Ca(2+) and chelators by contraction and expansion, respectively, and did not lose fluorescence in the process. Wild-type forisomes showed no affinity for free GFP in vitro. The three proteins shared numerous conserved motifs between themselves and with hypothetical proteins derived from the genomes of M. truncatula, Vitis vinifera and Arabidopsis thaliana. However, they showed neither significant similarities to proteins of known function nor canonical metal-binding motifs. We conclude that 'FOR'-like proteins are components of forisomes that are encoded by a well-defined gene family with relatives in taxa that lack forisomes. Since the mnemonic FOR is already registered and in use for unrelated genes, we suggest the acronym SEO (sieve element occlusion) for this family. The absence of binding sites for divalent cations suggests that the Ca(2+) binding responsible for forisome contraction is achieved either by as yet unidentified additional proteins, or by SEO proteins through a novel, uncharacterized mechanism.
authors.affiliation: School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
authors.forename: Hélène C
authors.initials: HC
authors.lastname: Pélissier
authors.forename: Winfried S
authors.initials: WS
authors.lastname: Peters
authors.forename: Ray
authors.initials: R
authors.lastname: Collier
authors.forename: Aart J E
authors.initials: AJ
authors.lastname: van Bel
authors.forename: Michael
authors.initials: M
authors.lastname: Knoblauch
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D003285:Contractile Proteins / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism*; D046913:Medicago truncatula / Q000235:genetics* / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D018749:RNA, Plant / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D013025:Glycine max / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D031307:Vicia faba / Q000235:genetics / Q000378:metabolism*
chemical_list: D003285:Contractile Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D002118:Calcium
references.citation: Nat Mater. 2003 Sep;2(9):600-3
references.pmid: 12942070
references.citation: Ann Bot. 2007 Jul;100(1):101-9
references.pmid: 17584851
references.citation: Funct Plant Biol. 2007 May;34(4):302-306
references.pmid: 32689356
references.citation: J Mol Biol. 2004 Oct 29;343(4):971-84
references.pmid: 15476814
references.citation: Plant Physiol. 1975 Nov;56(5):555-69
references.pmid: 16659345
references.citation: Proteins. 2006 Nov 15;65(3):643-55
references.pmid: 16981205
references.citation: J Exp Bot. 2006;57(14):3563-73
references.pmid: 16968882
references.citation: Plant Mol Biol. 2007 Oct;65(3):285-94
references.pmid: 17694275
references.citation: Methods Enzymol. 1996;266:513-25
references.pmid: 8743703
references.citation: Antioxid Redox Signal. 2007 Aug;9(8):1035-57
references.pmid: 17567240
references.citation: Mol Plant Microbe Interact. 2001 Dec;14(12):1364-7
references.pmid: 11768530
references.citation: Plant Cell. 1992 Dec;4(12):1539-48
references.pmid: 1467652
references.citation: Plant J. 2005 Aug;43(3):449-57
references.pmid: 16045479
references.citation: Cell Motil Cytoskeleton. 2004 Jul;58(3):137-42
references.pmid: 15146533
references.citation: Plant Cell. 1997 Jul;9(7):1137-1146
references.pmid: 12237379
references.citation: Cell Motil Cytoskeleton. 2008 May;65(5):368-78
references.pmid: 18330907
references.citation: Biophys Chem. 2007 Feb;125(2-3):444-52
references.pmid: 17125904
references.citation: Genome Res. 2003 Jun;13(6B):1430-42
references.pmid: 12819142
references.citation: Plant Physiol. 2007 Jun;144(2):588-93
references.pmid: 17556522
references.citation: Int J Plant Genomics. 2008;2008:256597
references.pmid: 18288239
references.citation: Cell Mol Life Sci. 2004 Oct;61(19-20):2497-509
references.pmid: 15526157
references.citation: Nat Mater. 2003 Sep;2(9):573-4
references.pmid: 12951596
references.citation: Plant Cell Environ. 2006 Sep;29(9):1715-29
references.pmid: 16913861
references.citation: Plant Cell. 2001 May;13(5):1221-30
references.pmid: 11340193
references.citation: Plant Physiol. 2003 Jan;131(1):114-28
references.pmid: 12529520
references.citation: J Eukaryot Microbiol. 1999 Mar-Apr;46(2):165-73
references.pmid: 10361738
references.citation: Plant Cell. 1999 Jan;11(1):127-40
references.pmid: 9878637
references.citation: Funct Plant Biol. 2007 May;34(4):282-291
references.pmid: 32689354
references.citation: Plant Physiol. 2004 Jul;135(3):1179-97
references.pmid: 15266052