Did Convergent Protein Evolution Enable Phytoplasmas to Generate ‘Zombie Plants’?

Phytoplasmas are pathogenic bacteria that reprogram plant development such that leaf-like structures instead of floral organs develop. Infected plants are sterile and mainly serve to propagate phytoplasmas and thus have been termed ‘zombie plants’. The developmental reprogramming relies on specific interactions of the phytoplasma protein SAP54 with a small subset of MADS-domain transcription factors. Here, we propose that SAP54 folds into a structure that is similar to that of the K-domain, a protein–protein interaction domain of MADS-domain proteins. We suggest that undergoing convergent structural and sequence evolution, SAP54 evolved to mimic the K-domain. Given the high specificity of resulting developmental alterations, phytoplasmas might be used to study flower development in genetically intractable plants.

TrendsThe phytoplasma effector protein SAP54 induces the formation of leaf-like organs instead of flowers.SAP54 specifically binds to the protein–protein interacting K-domain of MADS-domain proteins to reprogram flower development.Based on its recently solved X-ray crystal structure, the K-domain forms two α-helices separated by a kink region.In silico analysis of SAP54 indicates that it folds into a structure that is similar to that of the K-domain.We suggest that SAP54 underwent convergent sequence evolution to mimic the K-domain of its targets. This enabled it to interact with its MADS-domain protein targets and thereby manipulate plant development to its own benefit.