Phytoplasmas: Molecular Characterization and Host–Pathogen Interactions (2nd Edition)

A special issue of Biology (ISSN 2079-7737). This special issue belongs to the section "Microbiology".

Deadline for manuscript submissions: 31 July 2025 | Viewed by 3647

Special Issue Editor

USDA ARS Beltsville Agricultural Research Center, Beltsville, MD 20705, USA
Interests: insect-transmissible plant pathogenic mollicutes; host-pathogen interactions; phytoplasma taxonomy and classification; phytoplasma database construction; high throughput omics studies; molecular diagnosis and epidemiology
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Special Issue Information

Dear Colleagues,

This collection is the second edition of “Phytoplasmas: Molecular Characterization and Host–Pathogen Interactions”. Phytoplasmas are obligate intracellular bacteria that infect a wide variety of plant species and multiply in phloem-feeding insects in the order Hemiptera. The transkingdom life cycle of phytoplasma determines the complexity of its pathosystem and epidemiology in a broad range of ecological environments. Based on molecular characterization and database-guided identification and classification, significant advances have been achieved in phytoplasma studies in terms of genetic diversity and geographic distribution (in both managed agroecosystems and natural habitats), potential insect vectors, and new host plants, including symptomatic and asymptomatic weed reservoirs. The accumulating data on “phytoplasma–vector–plant” tripartite components provides a solid basis for understanding phytoplasma epidemiology and disease management.

In recent decades, studies on host–phytoplasma interactions have involved not only molecular analysis (“bottom-up approach” of systems biology at a small scale) but also high-throughput omics studies (“top-down approach” of systems biology at a large scale) such as genomics, transcriptomics, proteomics, and metabolomics. Combining “top-down” and “bottom-up” research approaches, host–phytoplasma interaction research has made tremendous progress in exploration from disease symptoms to underlying mechanisms, including the identification of virulence factors corresponding to symptoms and changes in the host response induced by phytoplasmas. These new advances contribute to a better understanding of the role of host–phytoplasma interactions in complex pathogenic processes and biological and physiological pathways involved in disease development and transmission.

For this Special Issue of Biology, we invite you to submit original research articles, reviews, opinions, and perspectives on the molecular characterization of phytoplasmas and host–phytoplasma interactions in various aspects.

We look forward to receiving your contributions.

Dr. Wei Wei
Guest Editor

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Keywords

  • molecular diagnosis and epidemiology
  • host-phytoplasma interactions
  • genetic diversity
  • taxonomy and classification
  • ecology and evolution
  • insect vectors
  • disease management
  • phytoplasma genomics and other omics studies

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Published Papers (3 papers)

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Research

14 pages, 7158 KiB  
Article
A Sec-Dependent Effector from “Candidatus Phytoplasma ziziphi” Suppresses Plant Immunity and Contributes to Pathogenicity
by Cui-Ping Wan, Fu-Xin He, Wei Zhang, Qian Xu, Qi-Liang Zhu and Chuan-Sheng Song
Biology 2025, 14(5), 528; https://doi.org/10.3390/biology14050528 - 10 May 2025
Viewed by 199
Abstract
Jujube witches’ broom (JWB) disease, caused by Candidatus Phytoplasma ziziphi (Ca. P. ziziphi), severely threatens the production of Chinese jujube (Ziziphus jujuba Mill.). Emerging evidence highlights the critical role of phytoplasma-secreted effectors in pathogenesis, though few have been functionally characterized. [...] Read more.
Jujube witches’ broom (JWB) disease, caused by Candidatus Phytoplasma ziziphi (Ca. P. ziziphi), severely threatens the production of Chinese jujube (Ziziphus jujuba Mill.). Emerging evidence highlights the critical role of phytoplasma-secreted effectors in pathogenesis, though few have been functionally characterized. Here, we identified a Sec-dependent effector, JWB790, from Ca. P. ziziphi, which was shown to suppress plant immunity. Through transient expression assays in Nicotiana benthamiana, pathogen inoculation assays, the generation of transgenic Arabidopsis thaliana plants, and RNA-seq-based transcriptomic profiling, we systematically investigated the virulence function of JWB790. Our findings revealed that JWB790 is highly expressed in JWB-infected tissues. The transient expression of JWB790 in N. benthamiana suppressed BAX-induced cell death and H2O2 accumulation. Furthermore, the stable overexpression of JWB790 in A. thaliana compromised disease resistance, accompanied by reduced H2O2 accumulation and callose deposition triggered by flg22. Additionally, the RNA-seq analysis of JWB790 transgenic Arabidopsis plants indicated that the overexpression of JWB790 altered the expression of biotic stress-related genes. In summary, JWB790 is a virulence factor that suppresses plant immunity and promotes pathogen proliferation. These results advance our understanding of Ca. P. ziziphi pathogenesis. Full article
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13 pages, 6011 KiB  
Article
Molecular Variation and Phylogeny of Thymidylate Kinase Genes of Candidatus Phytoplasma ziziphi from Different Resistant and Susceptible Jujube Cultivars in China
by Chuan-Sheng Song, Qi-Cong Xu, Cui-Ping Wan, De-Zhi Kong, Cai-Li Lin and Shao-Shuai Yu
Biology 2024, 13(11), 886; https://doi.org/10.3390/biology13110886 - 30 Oct 2024
Viewed by 966
Abstract
The thymidylate kinase (tmk) gene is indispensable for the proliferation and survival of phytoplasma. To reveal the molecular variation and phylogeny of the tmk genes of Candidatus phytoplasma ziziphi, in this study, the tmk genes of 50 phytoplasma strains infecting different [...] Read more.
The thymidylate kinase (tmk) gene is indispensable for the proliferation and survival of phytoplasma. To reveal the molecular variation and phylogeny of the tmk genes of Candidatus phytoplasma ziziphi, in this study, the tmk genes of 50 phytoplasma strains infecting different resistant and susceptible jujube cultivars from different regions in China were amplified and analyzed. Two sequence types, tmk-x and tmk-y, were identified using clone-based sequencing. The JWB phytoplasma strains were classified into three types, type-X, type-Y, and type-XY, based on the sequencing chromatograms of the tmk genes. The type-X and type-Y strains contained only tmk-x and tmk-y genes, respectively. The type-XY strain contained both tmk-x and tmk-y genes. The type-X, type-Y, and type-XY strains comprised 42%, 12%, and 46% of all the strains, respectively. The type-X and type-XY strains were identified in both susceptible and resistant jujube cultivars, while type-Y strain was only identified in susceptible cultivars. Phylogenetic analysis indicated that the tmk genes of the phytoplasmas were divided into two categories: phylo-S and phylo-M. The phylo-S tmk gene was single-copied in the genome, with an evolutionary pattern similar to the 16S rRNA gene; the phylo-M tmk gene was multi-copied, related to PMU-mediated within-genome transposition and between-genome transfer. Furthermore, the phylogenetic tree suggested that the tmk genes shuttled between the genomes of the Paulownia witches’ broom phytoplasma and JWB phytoplasma. These findings provide insights into the evolutionary and adaptive mechanisms of phytoplasmas. Full article
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10 pages, 1613 KiB  
Article
iPhyDSDB: Phytoplasma Disease and Symptom Database
by Wei Wei, Jonathan Shao, Yan Zhao, Junichi Inaba, Algirdas Ivanauskas, Kristi D. Bottner-Parker, Stefano Costanzo, Bo Min Kim, Kailin Flowers and Jazmin Escobar
Biology 2024, 13(9), 657; https://doi.org/10.3390/biology13090657 - 24 Aug 2024
Cited by 1 | Viewed by 1998
Abstract
Phytoplasmas are small, intracellular bacteria that infect a vast range of plant species, causing significant economic losses and impacting agriculture and farmers’ livelihoods. Early and rapid diagnosis of phytoplasma infections is crucial for preventing the spread of these diseases, particularly through early symptom [...] Read more.
Phytoplasmas are small, intracellular bacteria that infect a vast range of plant species, causing significant economic losses and impacting agriculture and farmers’ livelihoods. Early and rapid diagnosis of phytoplasma infections is crucial for preventing the spread of these diseases, particularly through early symptom recognition in the field by farmers and growers. A symptom database for phytoplasma infections can assist in recognizing the symptoms and enhance early detection and management. In this study, nearly 35,000 phytoplasma sequence entries were retrieved from the NCBI nucleotide database using the keyword “phytoplasma” and information on phytoplasma disease-associated plant hosts and symptoms was gathered. A total of 945 plant species were identified to be associated with phytoplasma infections. Subsequently, links to symptomatic images of these known susceptible plant species were manually curated, and the Phytoplasma Disease Symptom Database (iPhyDSDB) was established and implemented on a web-based interface using the MySQL Server and PHP programming language. One of the key features of iPhyDSDB is the curated collection of links to symptomatic images representing various phytoplasma-infected plant species, allowing users to easily access the original source of the collected images and detailed disease information. Furthermore, images and descriptive definitions of typical symptoms induced by phytoplasmas were included in iPhyDSDB. The newly developed database and web interface, equipped with advanced search functionality, will help farmers, growers, researchers, and educators to efficiently query the database based on specific categories such as plant host and symptom type. This resource will aid the users in comparing, identifying, and diagnosing phytoplasma-related diseases, enhancing the understanding and management of these infections. Full article
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