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Molecular sabotage of plant defense by aphid saliva.

ABSTRACT: 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 calcium-triggered 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 45Ca2+ 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.

SUBMITTER: Will T

PROVIDER: S-EPMC1965548 | biostudies-other | 2007 Jun

REPOSITORIES: biostudies-other

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Molecular sabotage of plant defense by aphid saliva.

Will Torsten T Tjallingii W Fred WF Thönnessen Alexandra A van Bel Aart J E AJ

Proceedings of the National Academy of Sciences of the United States of America 20070606 25

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 calcium-triggered and may be prevented by chemical constituents in aphid saliva injected into sieve tubes before and duri ...[more]

PMID: 17553961

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Project description:A pair of nearly isogenic tomato (Solanum lycopersicum) lines were used. These are: Motelle (Mi/Mi), root-knot nematode resistant and Moneymaker (mi/mi) root-knot nematode susceptible. A potato aphid (red biotype), imported from France, was used for infestation. An equal volume of sterile 1% carboxymethyl cellulose in water was added to the cleaned nematodes to keep them in suspension. The inoculum, consisting of 75-100 J2s, was dispensed in 10 µl aliquots using a repeat pipetter. The inoculum was pipetted 2 mm beneath the root tips. Control seedlings were inoculated with 0.5% carboxymethyl cellulose. After the desired incubation time (24 h or 36 h), seedlings were taken out of the boxes and a few set aside to check nematode infection rate. In our hand, this system results in 50% infection rate. The rest of the seedlings were placed on a water-saturated filter paper and the roots aligned. About 1 cm of the infected root tip was excised with a blade and quickly frozen on a polycarbonate membrane-lined 50 mm diameter Petri dish floating on liquid nitrogen and stored at -80C. Plants were grown for 6 weeks in a growth chamber under 16 h light/8 h dark at 25C in UCMix/sand, irrigated with water or MiracleGroR solution, then moved to an insect growth room (25C) 4-6 days before aphid infestation. Individual tomato leaflets were infested with 30-40 mixed stages of the potato aphids using plastic leaf cages. Four leaflets and two plants of each genotype were infested. Two plants of each genotype were used as controls. After the desired infestation time (6, 12, 24 or 48 h), leaflets were excised from the plants with a blade and sprayed with 1% SDS to force aphids to remove their stylets from the leaf tissue. Aphids were carefully removed from the leaflets and quickly frozen in liquid nitrogen. Control leaflets were excised and sprayed with 1% SDS before freezing. Samples were stored at -80C. RNA was isolated using the hot phenol method. Keywords: Direct comparison

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Molecular sabotage of plant defense by aphid saliva.

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Molecular sabotage of plant defense by aphid saliva.

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