The Regulation of Gelation of Phloem Exudate from <i>Cucurbita</i> Fruit by Dilution, Glutathione, and Glutathione Reductase

Alosi, M. Carol; Melroy, Diane L.; Park, R B

doi:10.1104/pp.86.4.1089

Cited by 90 publications

(68 citation statements)

References 25 publications

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“…Unlike forisomes, other proteins involved in SE plugging are more dispersed or even diluted in the phloem sap of other plant families (16). They will probably coagulate because of extraction procedures, high ambient oxygen concentrations (38), or a change of the SE redox potential (14,15).…”

Section: Resultsmentioning

confidence: 99%

Molecular sabotage of plant defense by aphid saliva

Will

Tjallingii

Thönnessen

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

455

413

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Aphids, which constitute one of the most important groups of agricultural pests, ingest nutrients from sieve tubes, the photoassimilate transport conduits in plants. Aphids are able to successfully puncture sieve tubes with their piercing mouthparts (stylets) and ingest phloem sap without eliciting the sieve tubes' normal occlusion response to injury. Occlusion mechanisms are calciumtriggered and may be prevented by chemical constituents in aphid saliva injected into sieve tubes before and during feeding. We recorded aphid feeding behavior with the electrical penetration graph (EPG) technique and then experimentally induced sieve tube plugging. Initiation of sieve tube occlusion caused a change in aphid behavior from phloem sap ingestion to secretion of watery saliva. Direct proof of ''unplugging'' properties of aphid saliva was provided by the effect of aphid saliva on forisomes. Forisomes are proteinaceous inclusions in sieve tubes of legumes that show calcium-regulated changes in conformation between a contracted state (below calcium threshold) that does not occlude the sieve tubes and a dispersed state (above calcium threshold) that occludes the sieve tubes. We demonstrated in vitro that aphid saliva induces dispersed forisomes to revert back to the nonplugging contracted state. Labeling Western-blotted saliva proteins with 45 Ca 2؉ or ruthenium red inferred the presence of calcium-binding domains. These results demonstrate that aphid saliva has the ability to prevent sieve tube plugging by molecular interactions between salivary proteins and calcium. This provides aphids with access to a continuous flow of phloem sap and is a critical adaptation instrumental in the evolutionary success of aphids.calcium-binding ͉ plant-aphid interaction ͉ plugging ͉ saliva proteins ͉ sieve element

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Section: Resultsmentioning

confidence: 99%

Molecular sabotage of plant defense by aphid saliva

Will

Tjallingii

Thönnessen

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

455

413

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“…Given its scarcity in sugar-transporting fascicular phloem and its abundance in extrafascicular phloem, PP1 is unlikely to belong to this group of conventional P-proteins. However, Cucurbita exudates, predominantly comprising the contents of the extrafascicular phloem, have a strong tendency to gel (54,55), and this property may be attributable to PP1 (18). Therefore PP1-based gelling could represent an alternative wound-sealing mechanism to sieve plate occlusion by SEO proteins deployed in fascicular sieve tubes.…”

Section: Distribution Of Seo Genes Reveals the Uniformity Of P-proteinsmentioning

confidence: 99%

Sieve element occlusion(SEO) genes encode structural phloem proteins involved in wound sealing of the phloem

Ernst

Jekat

Zielonka

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

100

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The sieve element occlusion (SEO) gene family originally was delimited to genes encoding structural components of forisomes, which are specialized crystalloid phloem proteins found solely in the Fabaceae. More recently, SEO genes discovered in various nonFabaceae plants were proposed to encode the common phloem proteins (P-proteins) that plug sieve plates after wounding. We carried out a comprehensive characterization of two tobacco (Nicotiana tabacum) SEO genes (NtSEO). Reporter genes controlled by the NtSEO promoters were expressed specifically in immature sieve elements, and GFP-SEO fusion proteins formed parietal agglomerates in intact sieve elements as well as sieve plate plugs after wounding. NtSEO proteins with and without fluorescent protein tags formed agglomerates similar in structure to native Pprotein bodies when transiently coexpressed in Nicotiana benthamiana, and the analysis of these protein complexes by electron microscopy revealed ultrastructural features resembling those of native P-proteins. NtSEO-RNA interference lines were essentially devoid of P-protein structures and lost photoassimilates more rapidly after injury than control plants, thus confirming the role of P-proteins in sieve tube sealing. We therefore provide direct evidence that SEO genes in tobacco encode P-protein subunits that affect translocation. We also found that peptides recently identified in fascicular phloem P-protein plugs from squash (Cucurbita maxima) represent cucurbit members of the SEO family. Our results therefore suggest a common evolutionary origin for P-proteins found in the sieve elements of all dicotyledonous plants and demonstrate the exceptional status of extrafascicular P-proteins in cucurbits.photoassimilate transport | wound response | exudation | phloem protein 1

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“…PD constriction is reached by Ca 2+ -dependent 9 deposition of β-1,3-glucane polymers (callose) into the apoplast, caused by activation of membrane-associated callose synthase (β-1,3-glucan synthase); PD re-opening is achieved by a callose-degrading membrane-associated β-1,3-glucanase. 10 In complement sieve-tubes are occluded by structural 7,4 or, possibly, water-soluble proteins 11 ( Fig. 1).…”

Section: Modes Of Sieve-plate Occlusionmentioning

confidence: 99%

“…Upon phloem injury, sieve elements (SEs) are occluded by combined callose-collar formation around sieve pores 1,2 and protein plugging [3][4][5][6] to prevent leakage of nutrients and invasion of phytopathogens. 7 Given the fact that sieve pores are modified plasmodesmata (PDs), 8 callose synthesis around PDs and sieve pores may strongly resemble.…”

Section: Modes Of Sieve-plate Occlusionmentioning

confidence: 99%