Abstract
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.
Highlights
Phytoplasmas are specialized obligate bacteria at the phloem tissue of plant and are transmitted by insect vectors [1]
Understanding the plant responses to pathogen infection requires a comprehensive evaluation of the changes in the gene expression profiles induced by pathogens
RNA-Seq and digital gene expression (DGE) techniques, based on generation sequencing, are powerful methods that are used to study gene expression changes in plant hosts induced by pathogen infection, especially for plants where the genome sequence is not unavailable [22]
Summary
Phytoplasmas are specialized obligate bacteria at the phloem tissue of plant and are transmitted by insect vectors [1]. It has been shown that ‘Bois noir’ Phytoplasma interacted with carbohydrate metabolism and down-regulated several photosynthetic genes in infected grapes, whereas defense genes, such as flavonoid metabolism-related and some pathogenesis related (PR) genes, were significantly upregulated [7]. The genes responsible for cell wall degradation were repressed in Chardonnay and Manzoni grape cultivars infected by ‘Bois noir’ Phytoplasma, whereas the genes involved in cell wall reinforcement were induced [8]. These studies have broadened our understanding of Phytoplasma pathogenesis and host defenses, but the physiological, biochemical and molecular mechanisms underlying disease symptom development are still poorly understood, because the inability of culturing phytoplasmas
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