Ginkgo biloba Responds to Herbivory by Activating Early Signaling and Direct Defenses

Background: Ginkgo biloba (Ginkgoaceae) is one of the most ancient living seed plants and is regarded as a living fossil. G. biloba has a broad spectrum of resistance or tolerance to many pathogens and herbivores because of the presence of toxic leaf compounds. Little is known about early and late events occurring in G. biloba upon herbivory. The aim of this study was to assess whether herbivory by the generalist Spodoptera littoralis was able to induce early signaling and direct defense in G. biloba by evaluating early and late responses. Methodology/Principal Findings: Early and late responses in mechanically wounded leaves and in leaves damaged by S. littoralis included plasma transmembrane potential (Vm) variations, time-course changes in both cytosolic calcium concentration ([Ca 2+]cyt) and H2O2 production, the regulation of genes correlated to terpenoid and flavonoid biosynthesis, the induction of direct defense compounds, and the release of volatile organic compounds (VOCs). The results show that G. biloba responded to hebivory with a significant Vm depolarization which was associated to significant increases in both [Ca 2+] cyt and H 2O 2. Several defense genes were regulated by herbivory, including those coding for ROS scavenging enzymes and the synthesis of terpenoids and flavonoids. Metabolomic analyses revealed the herbivore-induced production of several flavonoids and VOCs. Surprisingly, no significant induction by herbivory was found for two of the most characteristic G. biloba classes of bioactive compounds; ginkgolides and bilobalides

Peroxidase-dependent apoplastic oxidative burst in Arabidopsis required for pathogen resistance

The oxidative burst is an early response to pathogen attack leading to the production of reactive oxygen species (ROS) including hydrogen peroxide. Two major mechanisms involving either NADPH oxidases or peroxidases that may exist singly or in combination in different plant species have been proposed for the generation of ROS. We identified an Arabidopsis thaliana azide-sensitive but diphenylene iodonium-insensitive apoplastic oxidative burst that generates H2O2 in response to a Fusarium oxysporum cell-wall preparation. Transgenic Arabidopsis plants expressing an anti-sense cDNA encoding a type III peroxidase, French bean peroxidase type 1 (FBP1) exhibited an impaired oxidative burst and were more susceptible than wild-type plants to both fungal and bacterial pathogens. Transcriptional profiling and RT-PCR analysis showed that the anti-sense (FBP1) transgenic plants had reduced levels of specific peroxidase-encoding mRNAs, including mRNAs corresponding to Arabidopsis genes At3g49120 (AtPCb) and At3g49110 (AtPCa) that encode two class III peroxidases with a high degree of homology to FBP1. These data indicate that peroxidases play a significant role in generating H2O2 during the Arabidopsis defense response and in conferring resistance to a wide range of pathogens. The Additional file attached below is an Excel spreadsheet of 22,000+ lines containing Supplementary Materials. A PDF version (289 pages) is attached to the main downloadable document

Data from: Small RNAs from a big genome: the piRNA pathway and transposable elements in the salamander species Desmognathus fuscus

Most of the largest vertebrate genomes are found in salamanders, a clade of amphibians that includes 686 species. Salamander genomes range in size from 14 to 120 Gb, reflecting the accumulation of large numbers of transposable element (TE) sequences from all three TE classes. Although DNA loss rates are slow in salamanders relative to other vertebrates, high levels of TE insertion are also likely required to explain such high TE loads. Across the Tree of Life, novel TE insertions are suppressed by several pathways involving small RNA molecules. In most known animals, TE activity in the germline is primarily regulated by the Piwi-interacting RNA (piRNA) pathway. In this study, we test the hypothesis that salamanders’ unusually high TE loads reflect the loss of the ancestral piRNA-mediated TE-silencing machinery. We characterized the small RNA pool in the female and male adult gonads, testing for the presence of small RNA molecules that bear the characteristics of TE-targeting piRNAs. We also analyzed the amino acid sequences of piRNA pathway proteins from salamanders and other vertebrates, testing whether the overall patterns of sequence divergence are consistent with conserved pathway function across the vertebrate clade. Our results do not support the hypothesis of piRNA pathway loss; instead, they suggest that the piRNA pathway is expressed in salamanders. Given these results, we propose hypotheses to explain how the extraordinary TE loads in salamander genomes could have accumulated, despite the expression of TE-silencing machinery