Project description:BACKGROUND:JWB phytoplasma is a kind of insect-transmitted and uncultivable bacterial plant pathogen causeing a destructive Jujube disease. To date, no genome information about JWB phytoplasma has been published, which hindered its characterization at genomic level. To understand its pathogenicity and ecology, the genome of a JWB phytoplasma isolate jwb-nky was sequenced and compared with other phytoplasmas enabled us to explore the mechanisms of genomic rearrangement. RESULTS:The complete genome sequence of JWB phytoplasma (jwb-nky) was determined, which consisting of one circular chromosome of 750,803 bp with a GC content of 23.3%. 694 protein-encoding genes, 2 operons for rRNA genes and 31 tRNA genes as well as 4 potential mobile units (PMUs) containing clusters of DNA repeats were identified. Based on PHIbaes analysis, a large number of genes were genome-specific and approximately 13% of JWB phytoplasma genes were predicted to be associated with virulence. Although transporters for maltose, dipeptides/oligopeptides, spermidine/putrescine, cobalt, Mn/Zn and methionine were identified, KEGG pathway analysis revealed the reduced metabolic capabilities of JWB phytoplasma. Comparative genome analyses between JWB phytoplasma and other phytoplasmas shows the occurrence of large-scale gene rearrangements. The low synteny with other phytoplasmas indicated that the expansion of multiple gene families/duplication probably occurred separately after differentiation. CONCLUSIONS:In this study, the complete genome sequence of a JWB phytoplasma isolate jwb-nky that causing JWB disease was reported for the first time and a number of species-specific genes were identified in the genome. The study enhanced our understandings about genomic basis and the pathogenicity mechanism of this pathogen, which will aid in the development of improved strategies for efficient management of JWB diseases.
Project description:Phytoplasmas are plant pathogenic bacteria that have no cell wall and are responsible for major crop losses throughout the world. Phytoplasma-infected plants show a variety of symptoms and the mechanisms they use to physiologically alter the host plants are of considerable interest, but poorly understood. In this study we undertook a detailed analysis of Paulownia infected by Paulownia witches'-broom (PaWB) Phytoplasma using high-throughput mRNA sequencing (RNA-Seq) and digital gene expression (DGE). RNA-Seq analysis identified 74,831 unigenes, which were subsequently used as reference sequences for DGE analysis of diseased and healthy Paulownia in field grown and tissue cultured plants. Our study revealed that dramatic changes occurred in the gene expression profile of Paulownia after PaWB Phytoplasma infection. Genes encoding key enzymes in cytokinin biosynthesis, such as isopentenyl diphosphate isomerase and isopentenyltransferase, were significantly induced in the infected Paulownia. Genes involved in cell wall biosynthesis and degradation were largely up-regulated and genes related to photosynthesis were down-regulated after PaWB Phytoplasma infection. Our systematic analysis provides comprehensive transcriptomic data about plants infected by Phytoplasma. This information will help further our understanding of the detailed interaction mechanisms between plants and Phytoplasma.
Project description:The EFSA Panel on Plant Health performed a pest categorisation for the Witches' broom disease of lime (Citrus aurantifolia) phytoplasma for the EU territory. The pest has been reported in a few countries in the Middle East and is not known to occur in the EU. The disease is caused by a well-defined phytoplasma strain in the 'Candidatus Phytoplasma aurantifolia' species, for which efficient molecular detection assays are available. The most important known natural host is Citrus aurantifolia, which is only grown for ornamental purposes in the EU. Sweet limes, rough lemon and trifoliate orange are also naturally infected by that phytoplasma. The latter can be transmitted by grafting also to some citrus species. Other citrus species were reported to be resistant; however, their susceptibility has been assessed only by symptom observations, and the possible presence of phytoplasmas in symptomless plants cannot be ruled out. The phytoplasma is transmitted by the leafhopper Hishimonus phycitis, which is not known to occur in the EU. There is no information on the vector status of other phloem feeding insects of citrus present in the EU. The pest is listed in Annex IIAI of Directive 2000/29/EC. The main pathways for entry, plants for planting and the vector insect, are closed by existing legislation on import of citrus plants. Nevertheless, should the pest enter, it could establish and spread. In countries where Witches' broom disease of lime (WBDL) is present, it has significant impact. The main knowledge gaps concern (1) and vertical transmission of the phytoplasma to H. phycitis eggs (2) lack of information regarding susceptibility of citrus crops grown in the EU (3) status of potential insect vectors in the EU. Therefore, the WBDL phytoplasma meets the criteria assessed by EFSA for consideration as a potential Union quarantine pest.