Reverse Zombification

Overview

Phytoplasmas are cell wall-less eubacteria that obligatorily parasitize and replicate in two very different hosts: plants and transmitting insects [1]. Phytoplasmas infect hundreds of plant species, including many important crops, and bring about devastating diseases by causing symptoms such as phyllody, virescence and witches’ broom syndrome. The plant disease phenotypes are caused by effector proteins that are secreted by phytoplasmas, such as SAP11, SAP54 and TENGU [1, 2]. SAP11 leads to the degradation of some TCP-type transcription factors of the host plant, which compromises the plant’s immune system [1, 4]. SAP54 targets MIKC-type MADS-domain transcription factors (MTFs) and mediates their degradation via the ubiquitin/26S proteasome pathway [2]. Some of the targeted MTFs are part of the ‘floral quartets’ which specify floral organ identity and this explains why SAP54 secretion leads to virescence and phyllody [2, 5, 6]. The target of TENGU is still unknown. In the field phytoplasma infection occur randomly at different stages of plant development. In order to study the impact of timing of effector protein expression on disease phenotypes during plant development, phytoplasma effectors (SAP54, SAP11 and TENGU) will be overexpressed at different stages of development of the model plant Arabidopsis thaliana under the control of an inducible promoter for phenotype analysis since expression of single effector proteins of AY-WB phytoplasma in A. thaliana often leads to the development of almost all the symptoms that characterize a phytoplasma infection. Phytoplasma-infected plants are often rendered sterile and mainly serve to reproduce phytoplasmas hence have been termed “zombie plants” [2, 3]. Unfortunately, there is no cure for phytoplasma associated diseases so far but sometimes plants are able to recover based on unknown mechanisms. Direct and indirect plant factors required for zombification will be identified by suppressor mutagenesis. Large amounts of seeds required for EMS mutagenesis will be obtained from the plants overexpressing effector proteins under control of an inducible promoter. The main goal of this study is to identify and characterize plant factors required for zombification of phytoplasma-infected plants.