Biology subjects

Saskia A Hogenhout

Publications and source records attributed to Saskia A Hogenhout.

3 recordsLinked to original sources

bioRxiv2016

An immuno-suppressive aphid saliva protein is delivered into the cytosol of plant mesophyll cells during feeding.

Herbivore selection of plant hosts and plant responses to insect colonization have been subjects of intense investigations. A growing body of evidence suggests that for successful colonization to occur, (effector/virulence) proteins in insect saliva must modulate plant defense responses to the benefit of the insect. A range of insect saliva proteins that modulate plant defense responses have been identified, but there is no direct evidence that these proteins are delivered into specific plant tissues and enter plant cells. Aphids and other sap-sucking insects of the order Hemiptera use their specialized mouthparts (stylets) to probe plant mesophyll cells, until they reach the phloem cells for long-term feeding. Here we show by immunogold-labeling of ultrathin sections of aphid feeding sites that an immuno-suppressive aphid effector localizes in the cytoplasm of mesophyll cells near aphid stylets, but not in cells further away from aphid feeding sites. In contrast, another aphid effector protein localizes in the sheaths composed of gelling saliva that surround the aphid stylets. Thus, insects deliver effectors directly into plant tissue. Moreover, different aphid effectors locate extracellularly in the sheath saliva or are introduced into the cytoplasm of plant cells.

Plant Biology↗

bioRxiv2016

A clonally reproducing generalist aphid pest colonises diverse host plants by rapid transcriptional plasticity of duplicated gene clusters

BackgroundThe prevailing paradigm of host-parasite evolution is that arms races lead to increasing specialisation via genetic adaptation. Insect herbivores are no exception, and the majority have evolved to colonise a small number of closely related host species. Remarkably, the green peach aphid, Myzus persicae, colonises plant species across 40 families and single M. persicae clonal lineages can colonise distantly related plants. This remarkable ability makes M. persicae a highly destructive pest of many important crop species.\n\nResultsTo investigate the exceptional phenotypic plasticity of M. persicae, we sequenced the M. persicae genome and assessed how one clonal lineage responds to host plant species of different families. We show that genetically identical individuals are able to colonise distantly related host species through the differential regulation of genes belonging to aphid-expanded gene families. Multigene clusters collectively up-regulate in single aphids within two days upon host switch. Furthermore, we demonstrate the functional significance of this rapid transcriptional change using RNA interference (RNAi)-mediated knock-down of genes belonging to the cathepsin B gene family. Knock-down of cathepsin B genes reduced aphid fitness, but only on the host that induced up-regulation of these genes.\n\nConclusionsPrevious research has focused on the role of genetic adaptation of parasites to their hosts. Here we show that the generalist aphid pest M. persicae is able to colonise diverse host plant species in the absence of genetic specialisation. This is achieved through rapid transcriptional plasticity of genes that have duplicated during aphid evolution.

Genomics↗

bioRxiv2016

A bacterial parasite effector mediates insect vector attraction in host plants independently of developmental changes

Parasites can take over their hosts and trigger dramatic changes in host appearance and behaviour that are typically interpreted as extended phenotypes to promote parasite survival and fitness1. For example, Toxoplasma gondii manipulates the behaviour of infected rodents to aid transmission to cats2 and parasitic trematodes of the genus Ribeiroia alter limb development in their amphibian hosts to facilitate predation by birds3. Plant parasites and pathogens also reprogram host development and morphology4. Phytoplasma parasites of plants induce extensive leaf-like flower phenotype (phyllody) in their host plants, presumably to attract insect vectors on which these bacteria depend for transmission5,6. However, it remains debatable whether morphological phenotypes, such as phyllody, are directly beneficial to the parasites or are side-products of parasite infection7,8. Previously, we found that phytoplasma virulence protein (effector) SAP54 binds and mediates degradation of host MADS-box transcription factors 26 (MTFs), regulatory hubs of plant development and hormone physiology, to induce phyllody and promote insect vector colonisation5. Here we show that plants heterologously expressing SAP54 are strongly attractive to insects, but surprisingly, insect attraction was independent of the presence of leaf-like flowers. Moreover, plants that produce leaf-like flowers in the absence of SAP54 did not attract insects. We conclude that the SAP54 effector mediates insect vector attraction in host plants by exploiting the role of its MTF targets in insect defence and that perturbation of floral development may be a secondary effect of the effector activity.

Plant Biology↗