Phytoplasma protein structurally mimics regulators of flower development

A phytoplasma protein can disrupt the molecular machinery that controls flower development by structurally mimicking host MADS-box transcription factors, according to an experimental study published in the Journal of Biological Chemistry . The researchers found that the protein, called PHYLOY, interacts with a broader range of combinations of these transcription factors than previously thought. The work used small-angle X-ray scattering at the European Synchrotron Radiation Facility in Grenoble, France, together with site-directed mutagenesis to identify molecular features responsible for the interactions.

The reported mechanism provides an explanation for how infection can convert sepals, petals, stamens and carpels into leaf-like structures. Phytoplasmas are bacteria transmitted to plants by insects. The disease has affected economically important crops including sunflowers, sesame and grapevine.

The source release also describes historical outbreaks of coconut lethal yellowing disease in Africa, reporting crop losses of up to 40% in Tanzania and 20% in Ghana. It states that climate change has increased the presence of insect vectors at more northern latitudes, which could expand the geographic reach of phytoplasma diseases. The present study examined a protein from Candidatus Phytoplasma asteris, onion yellows strain, and did not test whether climate change caused the molecular interactions it reports.

Plant MADS-box transcription factors help determine how flowers develop. According to the study summary, these proteins work together in groups of four, bind to DNA and activate genes associated with the production of particular floral parts. The research team examined how PHYLOY interacts with three important MADS-box transcription factors.

They performed small-angle X-ray scattering experiments on beamline BM29 at the European Synchrotron and used the resulting data to study associations between the pathogen protein and different combinations of floral regulators. The experiments showed that PHYLOY can engage a wider range of MADS-box combinations than had previously been recognized. ESRF scientist Mark Tully said the flexibility visible in the data appeared to correspond to interaction plasticity between PHYLOY and the host plant transcription factors.

To investigate which molecular features enabled those associations, the researchers altered individual parts of PHYLOY and the MADS-box proteins through site-directed mutagenesis. Depending on the modification, the changes prevented or enabled the relevant interactions. These results showed that PHYLOY recognizes specific features shared by different MADS-box transcription factors.

The researchers interpret this pattern as structural mimicry: the phytoplasma protein resembles components of the plant’s own developmental machinery closely enough to interfere with the normal assembly of active transcription-factor groups. By preventing MADS-box proteins from functioning together properly, PHYLOY changes the developmental identity of floral organs, leading to leaf-like structures. The evidence comes from laboratory experiments on the protein interaction and its molecular basis, rather than from a field assessment across infected crops.

The team is working toward a high-resolution crystal structure of the MADS-box transcription factor–PHYLOY complex. The researchers say they hope to combine those structural data with high-throughput virtual screening to design inhibitors of the interaction, but that remains a future objective. The peer-reviewed article, “The phytoplasma effector, phyllogen, structurally mimics host plant MADS transcription factors,” was published in the Journal of Biological Chemistry on 13 August 2026 and was selected as the journal’s Editor’s Pick.

The study was led by CEA researcher Chloe Zubieta, a visiting scientist at the European Synchrotron, together with ESRF scientists Mark Tully and Max Nanao.

Subject of Research: Structural mimicry of host MADS-box transcription factors by the phytoplasma effector PHYLOY

Article Title: How a pathogen turns flowers into leaves

Article References: How a pathogen turns flowers into leaves. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: phytoplasma, PHYLOY, flower development, MADS-box proteins, transcription factors, structural mimicry, small-angle X-ray scattering, plant disease, site-directed mutagenesis, insect vectors, pathogen, turns