Widespread targeting of development-related host transcription factors by phytoplasma effectors

Phytoplasmas are pathogenic bacteria that reprogram plant host development in order to attract their insect vectors to disseminate. Previous studies have characterized a few different phytoplasma effector proteins that supress specific transcription factors. However, these are only a small fraction of the potential effectors used by phytoplasmas, meaning that the molecular mechanisms through which phytoplasmas manipulate their hosts are largely uncharacterized. To obtain further insights into the phytoplasma infection mechanisms, we generated a protein-protein interaction network between a broad set of phytoplasma effectors and a large collection of Arabidopsis thaliana transcription factors and transcriptional regulators. We found widespread, but unique, interactions with host transcription factors by phytoplasma effectors, especially those related to developmental processes. In particular, many unrelated effectors target TCP transcription factors, which play roles in plant development and immunity. Comparison with other host-pathogen protein interaction networks shows that phytoplasma effectors have unusual targets, and indicates that phytoplasmas have evolved a unique and unusual infection strategy. This study provides a rich and solid data source that can be used to predict functional effects of individual effectors and as a guide for detailed studies of individual effectors in the future, as well as insights into the underlying molecular mechanisms of phytoplasma infection.