Phytoplasma-induced alterations in endophytic bacterial communities in Paulownia: implications for witches' broom

Paulownia witches' broom (PaWB), caused by phytoplasma, threatens global Paulownia cultivation. Although phytoplasma is known to manipulate host physiology, their influence on the plant-associated microbiome, particularly at the tissue-specific level, remains unclear. Here, we integrated scanning electron microscopy, nested PCR, and 16S rRNA sequencing to investigate the morphological characteristics, phytoplasma infection, and bacterial communities across four compartments (leaves, branches, roots, and rhizosphere) in healthy, symptomatic, and asymptomatic P. fortunei trees. We found that PaWB induces pronounced external morphological abnormalities without significantly altering internal tissue structures. Notably, phytoplasma was detected not only in symptomatic tissues but also at low abundance in asymptomatic compartments, indicating a latent infection state. Phytoplasma proliferation in symptomatic leaves and branches was accompanied by a dramatic loss of bacterial diversity and a collapse in microbial interaction network complexity, while the root and rhizosphere microbiota remained comparatively stable. Random forest modeling identified Candidatus phytoplasma and ten other bacterial genera as key predictors of PaWB status. Microbial function predictions further revealed that disrupted carbohydrate degradation and tryptophan metabolism in diseased tissues may promote the expansion of opportunistic microbes, potentially exacerbating PaWB symptom development. Our study provides the first compelling evidence that phytoplasma infection drives tissue-specific microbiome collapse in Paulownia, disrupting microbial networks and reprogramming functional pathways well before visible symptoms emerge. These previously unrecognized microbial and metabolic signatures represent robust early-warning biomarkers and offer strategic targets for precision diagnostics and disease intervention, marking a significant advance in our understanding and management of PaWB.

Paulownia witches' broom (PaWB) disease poses a severe threat to global Paulownia cultivation, yet its microbiome-related mechanisms remain poorly understood. Here, we show that phytoplasma infection alters the external P. fortunei morphology and disrupts the composition, structure, and function of endophytic bacterial communities in aerial tissues. These microbial shifts are closely linked to symptom development, with latent infections also detected in asymptomatic tissues. Eleven microbial markers, including Candidatus Phytoplasma, enable accurate disease prediction. Predictions of functional shifts in carbohydrate and tryptophan metabolism further implicate microbiome alterations in symptom development. Our study contributes to a deeper understanding of the complex interaction mechanism among Paulownia, microorganisms and phytoplasma during the occurrence of PaWB and offer a theoretical foundation for sustainable management of PaWB.