Development of phytoplasma-induced flower symptoms in Arabidopsis Thaliana

A reliable model for the study of the molecular events leading to floral symptoms during plant–phytoplasma interaction was established by developing an efficient protocol for the infection of Arabidopsis thaliana with the Italian Clover Phyllody (ICPh) phytoplasma. ICPh phytoplasma infection of different A. thaliana ecotypes resulted in a wide range of symptom patterns. Ecotype Col-0 was selected for the repeatable time course and the severity of flower developmental alterations. By inoculating Col-0 at 30 days after germination with ICPh phytoplasma in short day, flowers were produced with increasingly severe symptoms, from carpels modification to virescence, phyllody, loss of determinacy and loss of organ developmental pattern. Gene expression analysis showed strong down regulation of some homeotic genes involved in flowering and genes involved in the gibberellin metabolism. Common morphological features were detected in phytoplasma-infected wild type plants and healthy mutants impaired in the gene functions that were found to be down-regulated in the infected plants. Evidence from the analysis of morphological alterations and from the results of quantitative real time PCR pointed to a central role of the deregulation of SEPALLATA genes, that are involved in flower development and hormonal control.

► Symptoms caused by ICPh phytoplasma on different Arabidopsis thaliana ecotypes were diverse.
► A reliable model to study phytoplasma induced floral symptoms was established.
► Expression analysis showed down regulation of homeotic genes.
► Genes involved in gibberellin metabolism were also affected.
► A central role of the deregulation of SEP3 was assessed.