# Genomic insights into the pathogenicity of a ‘Candidatus Phytoplasma asteris’ associated with Trema levigata witches’ broom disease in China

## TL;DR

This study uses a culture-free method to analyze the genome of a phytoplasma causing witches' broom disease in a plant species in China.

## Contribution

The study presents a draft genome of a phytoplasma using a culture-independent approach, revealing its metabolic and pathogenic features.

## Key findings

- The phytoplasma genome is 849.7 kb with 1356 predicted genes, 587 of which are functionally annotated.
- The genome includes complete glycolysis and pyruvate metabolism pathways and specific transporters for host metabolites.
- Thirty-one putative secreted proteins and three potential mobile units were identified, suggesting mechanisms for pathogenicity.

## Abstract

Phytoplasma research encounters limitations due to the lack of availability of pure cultures of these microorganisms. In this study a culture-independent approach was employed to investigate the genome and pathogenic mechanisms of phytoplasma responsible for witches’ broom disease in Trema levigata (Yunnan province, China). The phytoplasma genome was assembled using Illumina sequencing data and the Phytoassembly pipeline based on mixed samples.

Nested PCR analysis identified a 16Sr group I, ‘Candidatus Phytoplasma asteris’ strain in Trema levigate showing witches’ broom disease. Comparative study between infected and healthy plants resulted in an 849.7 kb draft genome with 94.1% coverage, 27.6% GC content, encoding 1356 predicted genes, of which 587 were functionally annotated. Multilocus phylogenetic analysis showed that this phytoplasma is closely related to ‘Ca. P. asteris’. The genome possesses complete pathways for glycolysis and pyruvate metabolism pathways and harbors specific transporters (spermidine/putrescine, lysine), indicating dependency on host metabolites. Thirty-one putative secreted proteins, including TENGU and SAP05/54-like effectors were identified along with three potential mobile units carrying replication/recombination genes.

This approach demonstrates the effectiveness of pathogen purification-free analysis for phytoplasma studies in naturally infected host species, thereby enhancing the understanding of phytoplasma-host interactions.

The online version contains supplementary material available at 10.1186/s12870-025-07482-x.