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.ResultsTo 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 upregulate 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 upregulation of these genes.ConclusionsPrevious 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-1145-3) contains supplementary material, which is available to authorized users.

Human Papillomavirus (HPV) is the causal agent of cervical cancer, one of the most common causes of death for women. The major capsid L1 protein self-assembles in Virus Like Particles (VLPs), which are highly immunogenic and suitable for vaccine production. In this study, a plastid transformation approach was assessed in order to produce a plant-based HPV-16 L1 vaccine. Transplastomic plants were obtained after transformation with vectors carrying a chimeric gene encoding the L1 protein either as the native viral (L1(v) gene) or a synthetic sequence optimized for expression in plant plastids (L1(pt) gene) under control of plastid expression signals. The L1 mRNA was detected in plastids and the L1 antigen accumulated up to 1.5% total leaf proteins only when vectors included the 5'-UTR and a short N-terminal coding segment (Downstream Box) of a plastid gene. The half-life of the engineered L1 protein, determined by pulse-chase experiments, is at least 8 h. Formation of immunogenic VLPs in chloroplasts was confirmed by capture ELISA assay using antibodies recognizing conformational epitopes and by electron microscopy.

Production of recombinant subunit vaccines from genes incorporated in the plastid genome is advantageous because of the attainable expression level due to high transgene copy number and the absence of gene silencing; biocontainment as a consequence of maternal inheritance of plastids and no transgene presence in the pollen; and expression of multiple transgenes in prokaryotic-like operons. We discuss the core technology of plastid transformation in Chlamydomonas reinhardtii, a unicellular alga, and Nicotiana tabacum (tobacco), a flowering plant species, and demonstrate the utility of the technology for the production of recombinant vaccine antigens.

The possibility of altering the unsaturation level of fatty acids in plant lipids by genetic transformation has implications for the stress tolerance of higher plants as well as for their nutritional value and industrial utilisation. While the integration and expression of transgenes in the plastome has several potential advantages over nuclear transformation, very few attempts have been made to manipulate fatty acid biosynthesis using plastid transformation. We produced transplastomic tobacco plants that express a D 9 desaturase gene from either the wild potato species Solanum commersonii or the cyanobacterium Anacystis nidulans, using PEG-mediated DNA uptake by protoplasts. Incorporation of chloroplast antibioticinsensitive point mutations in the transforming DNA was used to select transformants. The presence of the transcript and the D 9 desaturase protein in transplastomic plants was confirmed by northern and western blot analyses. In comparison with control plants, transplastomic plants showed altered fatty acid profiles and an increase in their unsaturation level both in leaves and seeds. The two transgenes produced comparable results. The results obtained demonstrate the feasibility of using plastid transformation to engineer lipid metabolic pathways in both vegetative and reproductive tissues and suggest an increase of cold tolerance in transplastomic plants showing altered leaf fatty acid profiles. This is the first example of transplastomic plants expressing an agronomically relevant gene produced with the ''binding-type'' vectors, which do not contain a heterologous marker gene. In fact, the transplastomic plants expressing the S. commersonii gene contain only plant-derived sequences, a clear attraction from a public acceptability perspective.