Project description:Eucalyptus species and interspecific hybrids exhibit valuable growth and wood properties that make them a highly desirable commodity. However, these trees are challenged by a wide array of biotic stresses during their lifetimes. The Eucalyptus grandis reference genome sequence provides a resource to study pest and pathogen defence mechanisms in long-lived woody plants. E. grandis trees are generally susceptible to Chrysoporthe austroafricana, a causal agent of stem cankers on eucalypts. The aim of this study was to characterize the defence response of E. grandis against C. austroafricana.Hormone profiling of susceptible and moderately resistant clonal E. grandis genotypes indicated a reduction in salicylic acid and gibberellic acid levels at 3 days post inoculation. We hypothesized that these signaling pathways may facilitate resistance. To further investigate other defence mechanisms at this time point, transcriptome profiling was performed. This revealed that cell wall modifications and response to oxidative stress form part of the defence responses common to both genotypes, whilst changes in the hormone signaling pathways may contribute to resistance. Additionally the expression of selected candidate defence response genes was induced earlier in moderately resistant trees than in susceptible trees, supporting the hypothesis that a delayed defence response may occur in the susceptible interaction.The ability of a host to fine-tune its defence responses is crucial and the responses identified in this study extends our understanding of plant defence, gained from model systems, to woody perennials.
Project description:The gene expression profiles of the differentiating xylem of 91 Eucalyptus grandis backcross individuals were characterized following a loop design (Churchill, G.A. Nat Genet. 2002 Dec;32 Suppl:490-5). In this design, RNA from genotype 1666 (labeled with Cy5) was hybridized with RNA from genotype 1667 (labeled with Cy3) on the first slide(GEO accession number GSM7637); the same genotype 1667 (now labeled with Cy5) was compared with genotype 1669 (Cy3) on the second slide (GSM7638), and so on. The loop was completed when genotype 1666 (Cy3) was contrasted to individual 1796 (Cy3) on slide GSM7727. Therefore, 91 individuals (genotypes) from the E. grandis backcross population were analyzed in two replicates, one with RNA labeled with Cy3 and the other with Cy5. Keywords = Eucalyptus, xylem, microarray Keywords: ordered
Project description:BACKGROUND:Land plant organellar genomes have significant impact on metabolism and adaptation, and as such, accurate assembly and annotation of plant organellar genomes is an important tool in understanding the evolutionary history and interactions between these genomes. Intracellular DNA transfer is ongoing between the nuclear and organellar genomes, and can lead to significant genomic variation between, and within, species that impacts downstream analysis of genomes and transcriptomes. RESULTS:In order to facilitate further studies of cytonuclear interactions in Eucalyptus, we report an updated annotation of the E. grandis plastid genome, and the second sequenced and annotated mitochondrial genome of the Myrtales, that of E. grandis. The 478,813 bp mitochondrial genome shows the conserved protein coding regions and gene order rearrangements typical of land plants. There have been widespread insertions of organellar DNA into the E. grandis nuclear genome, which span 141 annotated nuclear genes. Further, we identify predicted editing sites to allow for the discrimination of RNA-sequencing reads between nuclear and organellar gene copies, finding that nuclear copies of organellar genes are not expressed in E. grandis. CONCLUSIONS:The implications of organellar DNA transfer to the nucleus are often ignored, despite the insight they can give into the ongoing evolution of plant genomes, and the problems they can cause in many applications of genomics. Future comparisons of the transcription and regulation of organellar genes between Eucalyptus genotypes may provide insight to the cytonuclear interactions that impact economically important traits in this widely grown lignocellulosic crop species.
Project description:The gene expression profiles of the differentiating xylem of 91 Eucalyptus grandis backcross individuals were characterized following a loop design (Churchill, G.A. Nat Genet. 2002 Dec;32 Suppl:490-5). In this design, RNA from genotype 1666 (labeled with Cy5) was hybridized with RNA from genotype 1667 (labeled with Cy3) on the first slide(GEO accession number GSM7637); the same genotype 1667 (now labeled with Cy5) was compared with genotype 1669 (Cy3) on the second slide (GSM7638), and so on. The loop was completed when genotype 1666 (Cy3) was contrasted to individual 1796 (Cy3) on slide GSM7727. Therefore, 91 individuals (genotypes) from the E. grandis backcross population were analyzed in two replicates, one with RNA labeled with Cy3 and the other with Cy5. Keywords = Eucalyptus, xylem, microarray
Project description:Eucalyptus grandis is a commercially important hardwood species and is known to be susceptible to a number of pests and pathogens. Determining mechanisms of defense is therefore a research priority. The published genome for E. grandis has aided the identification of one important class of resistance (R) genes that incorporate nucleotide binding sites and leucine-rich repeat domains (NBS-LRR). Using an iterative search process we identified NBS-LRR gene models within the E. grandis genome. We characterized the gene models and identified their genomic arrangement. The gene expression patterns were examined in E. grandis clones, challenged with a fungal pathogen (Chrysoporthe austroafricana) and insect pest (Leptocybe invasa). One thousand two hundred and fifteen putative NBS-LRR coding sequences were located which aligned into two large classes, Toll or interleukin-1 receptor (TIR) and coiled-coil (CC) based on NB-ARC domains. NBS-LRR gene-rich regions were identified with 76% organized in clusters of three or more genes. A further 272 putative incomplete resistance genes were also identified. We determined that E. grandis has a higher ratio of TIR to CC classed genes compared to other woody plant species as well as a smaller percentage of single NBS-LRR genes. Transcriptome profiles indicated expression hotspots, within physical clusters, including expression of many incomplete genes. The clustering of putative NBS-LRR genes correlates with differential expression responses in resistant and susceptible plants indicating functional relevance for the physical arrangement of this gene family. This analysis of the repertoire and expression of E. grandis putative NBS-LRR genes provides an important resource for the identification of novel and functional R-genes; a key objective for strategies to enhance resilience.
Project description:Fungi represent a common and diverse part of the microbial communities that associate with plants. They also commonly colonise various plant parts asymptomatically. The molecular mechanisms of these interactions are, however, poorly understood. In this study we use transcriptomic data from Eucalyptus grandis, to demonstrate that RNA-seq data are a neglected source of information to study fungal-host interactions, by exploring the fungal transcripts they inevitably contain. We identified fungal transcripts from E. grandis data based on their sequence dissimilarity to the E. grandis genome and predicted biological functions. Taxonomic classifications identified, amongst other fungi, many well-known pathogenic fungal taxa in the asymptomatic tissue of E. grandis. The comparison of a clone of E. grandis resistant to Chrysoporthe austroafricana with a susceptible clone revealed a significant difference in the number of fungal transcripts, while the number of fungal taxa was not substantially affected. Classifications of transcripts based on their respective biological functions showed that the fungal communities of the two E. grandis clones associate with fundamental biological processes, with some notable differences. To shield the greater host defence machinery in the resistant E. grandis clone, fungi produce more secondary metabolites, whereas the environment for fungi associated with the susceptible E. grandis clone is more conducive for building fungal cellular structures and biomass growth. Secreted proteins included carbohydrate active enzymes that potentially are involved in fungal-plant and fungal-microbe interactions. While plant transcriptome datasets cannot replace the need for designed experiments to probe plant-microbe interactions at a molecular level, they clearly hold potential to add to the understanding of the diversity of plant-microbe interactions.