No abstract

We describe a novel, typically prokaryotic, sensor kinase in chloroplasts of green plants. The gene for this chloroplast sensor kinase (CSK) is found in cyanobacteria, prokaryotes from which chloroplasts evolved. The CSK gene has moved, during evolution, from the ancestral chloroplast to the nuclear genomes of eukaryotic algae and green plants. The CSK protein is now synthesised in the cytosol of photosynthetic eukaryotes and imported into their chloroplasts as a protein precursor. In the model higher plant Arabidopsis thaliana, CSK is autophosphorylated and required for control of transcription of chloroplast genes by the redox state of an electron carrier connecting photosystems I and II. CSK therefore provides a redox regulatory mechanism that couples photosynthesis to gene expression. This mechanism is inherited directly from the cyanobacterial ancestor of chloroplasts, is intrinsic to chloroplasts, and is targeted to chloroplast genes. cell evolution ͉ chloroplast genome ͉ redox ͉ transcription ͉ two-component system

C₄ photosynthesis allows increased photosynthetic efficiency because carbon dioxide (CO₂) is concentrated around the key enzyme RuBisCO. Leaves of C₄ plants exhibit modified biochemistry, cell biology, and leaf development, but despite this complexity, C₄ photosynthesis has evolved independently in at least 45 lineages of plants. We found that two independent lineages of C₄ plant, whose last common ancestor predates the divergence of monocotyledons and dicotyledons about 180 million years ago, show conserved mechanisms controlling the expression of genes important for release of CO(2) around RuBisCO in bundle sheath (BS) cells. Orthologous genes from monocotyledonous and dicotyledonous C₃ species also contained conserved regulatory elements that conferred BS specificity when placed into C₄ species. We conclude that these conserved functional genetic elements likely facilitated the repeated evolution of C₄ photosynthesis.

The range of sap-sucking insect pests to which GNA, (the mannose specific lectin from snowdrops (Galanthus nivalis)) has been shown to be insecticidal in artificial diets has been extended to include the peach potato aphid (Myzuspersicae). A gene construct for constitutive expression of GNA from the CaMV35S gene promoter has been introduced into tobacco plants. A transgenic tobacco line which expresses high levels of GNA has been shown to have enhanced resistance to M. persicae in leaf disc and whole plant bioassays, demonstrating the potential for extending transgenic plant technology to the control of sap-sucking insect pests.

SummaryRotavirus VP6 is a highly immunogenic major capsid protein that may be useful as a subunit vaccine. The expression of a bovine group A rotavirus VP6 cDNA was examined in tobacco chloroplasts following particle bombardment. Constructs containing the VP6 cDNA under the control of plastid rrn or psbA promoters, or the Escherichia coli trc promoter, were inserted, together with the aadA selectable marker gene, between the rbcL and accD genes of the tobacco plastid genome. The 40-kDa VP6 protein accumulated to about 3% of total soluble protein in seedlings and young leaves of homoplasmic transplastomic plants containing the VP6 cDNA under the control of the rrn promoter. Lower amounts of VP6 ( ∼ 0.6% total soluble protein) accumulated in plants containing the VP6 cDNA under the control of the psbA promoter, and VP6 was undetectable in plants containing the VP6 cDNA under the control of the trc promoter. The VP6 protein in chloroplasts was shown to form trimers, as found in the rotavirus virion. However, the amount of VP6 protein declined as the leaves matured, although VP6 transcripts were still present, suggesting that the protein was susceptible to proteolytic degradation in chloroplasts.

Potato virus X (PVX) and potato virus Y (PVY) infection in potato may result in the loss of certification of seed potatoes and affect quality and yield of potatoes in commercial production. We transformed a major commercial cultivar of potato, Russet Burbank, with the coat protein genes of PVX and PVY. Transgenic plants that expressed both CP genes were resistant to infection by PVX and PVY by mechanical inoculation. One line was also resistant when PVY was inoculated with viruliferous green peach aphids. These experiments demonstrate that CP protection is effective against mixed infection by two different viruses and against mechanical and aphid transmission of PVY.

No abstract

Potato plants (Solanum tuberosum) cv. Desireé were transformed with the genes encoding the proteins bean chitinase (BCH), snowdrop lectin (GNA) and wheat α‐amylase inhibitor (WAI) under the control of the constitutive CaMV 35S promoter. Transgenic plants with detectable levels of foreign RNA were then selected for further characterisation with respect to protein expression levels by immunodot blot analysis using polyclonal antibodies raised against the respective protein. With the exception of WAI, plants expressing high levels of RNA, expressed correspondingly high levels of the foreign protein (1.5–2.0% of the total soluble protein). Although high levels of WAI mRNA were detected in some of the transformants, the protein could not be detected. On the bases of expression levels, two lines, designated PWG6#85 (transformed with the double construct WAI/GNA) and PBG6#47 (transformed with the double construct BCH/GNA), were selected for testing in aphid trials for enhanced levels of resistance. Both transgenic lines had a marked and significant effect on fecundity. The number of nymphs produced per female per day peaked at 4.1 and 4.2 for lines PBG6#47 and PWG6#85 respectively, compared to a value of 5.4 on control plants. Total nymphal production was also significantly lower on either of the transgenic lines compared to control plants (P<0.001) with the differences between the lines being only just significant (P=0.058). On line PBG6#47 there was a delay in nymphal production of 1.6 days, representing a delay of 1 5%, and on line PWG6#85 this was 3.2 days, representing a delay of ca. 30%. The intrinsic rates of increase (rm) were also significantly lower on both of the transgenic lines in comparison to that on control plants (P<0.001), however the differences between the lines were not significant. The potential of using such genes as part of an over all strategy for the control of aphid populations is discussed.