Guilt by association: DNA-barcoding based identification of potential plant hosts of phytoplasmas from their insect carriers

Authors: Inaba, Junichi; Shao, Jonathan; TRIVELLONE, VALERIA - Illinois Natural History Survey; Zhao, Yan; DIETRICH, CHRISTOPHER - Illinois Natural History Survey; Bottner, Kristi; IVANAUSKAS, ALGIRDAS - Nature Research Centre; Wei, Wei

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2023
Publication Date: 3/27/2023
Citation: Inaba, J., Shao, J.Y., Trivellone, V., Zhao, Y., Dietrich, C.H., Bottner-Parker, K.D., Ivanauskas, A., Wei, W. 2023. Guilt by association: DNA-barcoding based identification of potential plant hosts of phytoplasmas from their insect carriers. Phytopathology. 113(3):413-422. https://doi.org/10.1094/PHYTO-09-22-0323-R.
DOI: https://doi.org/10.1094/PHYTO-09-22-0323-R

Interpretive Summary: Phytoplasmas are bacterial pathogens that infect various plant species. Phytoplasma pathosystem consists of three key components: phytoplasma, insect vector and plant host. Our previous studies have demonstrated that the genetically diverse phytoplasmas were present in leafhoppers (potential insect vectors) collected from natural habitats. The next questions are, what are the potential plant hosts for these phytoplasmas carried by leafhoppers and what are the potential impacts on ecosystems? To answer these questions, ARS scientists located in Beltsville, Maryland, in collaboration with scientists in the University of Illinois, employed DNA barcoding (standardized short DNA region) for rapid and accurate identification of plant species. Based on a specific plant DNA barcode marker, 14 plant species were identified from the examined leafhopper specimens. These species include previously undocumented/potential new plant hosts of phytoplasmas. In addition, several known plant hosts were also recognized, such as tomato, alfalfa, and maize. Remarkably, tomatoes and maizes cultivated in well-managed croplands were found as food sources of some leafhoppers collected in natural habitats. This strongly indicates that phytoplasmas carried by leafhoppers have a potential spillover/spillback risk between the crop and non-crop regions. The findings will benefit the professors, researchers, and students who are interested in tripartite associations and interactions of pathogen-vector-plant. The present study will be helpful for phytoplasma disease forecasting and future surveillance.

Technical Abstract: Phytoplasmas are small phloem-restricted and insect-transmissible bacteria that infect many plant species including important crops and ornamental plants, causing severe economic losses. Our previous studies screened phytoplasmas in hundreds of leafhoppers collected from natural habitats worldwide and identified multiple genetically different phytoplasmas in seven leafhopper species (potential insect vectors). As an initial step toward determining the impact of these phytoplasmas on the ecosystem, ribulose 1,5-biphosphate carboxylase large subunit (rbcL), a commonly used plant DNA barcoding marker, was employed to identify the plant species that the phytoplasma-harboring leafhoppers feed on. DNAs of 17 individual leafhoppers were PCR amplified using universal rbcL primers. PCR products were cloned, and five clones per amplicon were randomly chosen for Sanger sequencing. Moreover, Illumina high-throughput sequencing on selected PCR products was conducted and confirmed no missing targets in Sanger sequencing. The nucleotide BLAST results revealed 14 plant species, including six well-known plant hosts of phytoplasmas such as tomato, alfalfa, and maize. The remaining species have not been documented as phytoplasma hosts, expanding our knowledge of potential plant hosts. Notably, DNAs of tomato and maize (apparently cultivated in well-managed croplands) were detected in some phytoplasma-harboring leafhopper species sampled in non-crop lands, suggesting the spillover/spillback risk of phytoplasma strains between crop and non-crop areas. Furthermore, our results indicate that barcoding (or metabarcoding) is a valuable tool to study the three-way interactions among phytoplasmas, plant hosts, and vectors. The findings contribute to a better understanding of phytoplasma host range, host shift, and disease epidemiology.