The Role of the EAR Domain in Transcriptional Repressors involved in Plant Defence

Abstract

Plants respond to abiotic and biotic stressors through hormone signalling which forms an integral part of the plant immune response, and is often the target of phytopathogens. Changes in hormone levels are often underpinned by transcriptional reprogramming driven by specific transcription factors (TF) which collectively regulate the spatial, temporal expression levels of hormone biosynthetic and signalling genes in a co-ordinated manner. This study examined two contrasting transcription repressors (TR) implicated in Arabidopsis - Pseudomonas syringae disease development;; a MYB like transcription factor (HUB37) and a JAsmonate Zim domain (JAZ) containing transcriptional repressors involved in jasmonate signalling. The MYB transcription factor was identified by modelling as a core hub in immune signalling, whereas JAZ5 was recently shown to co-operate with JAZ10 during transcriptional reprogramming, to restrict P. syringae growth and attenuated chlorosis. The transcriptional repressor ERF-associated Amphiphilic Repression (EAR) domains confer dominant transcriptional repressive functions. HUB37 contains one EAR domain and JAZ5 contains 2 EAR domains. Previous transcriptional inference modelling predicted HUB37 was a highly transcription factor that negatively regulated A. thaliana defence responses to P. syringae. This was validated by testing a HUB37 loss of function mutant (Siddharth Jayaraman, Marta de Torres per com). JAZ5 and JAZ10 are required for full immunity to P. syringae. Thus, this study sought to develop molecular and genetic tools to explore the role of the EAR domain in disease. Golden Gate cloning and targeted mutagenesis were used to generate epitope tagged lines of JAZ5 and HUB37 with and without EAR domains. These were assembled into T-DNA transformation vectors and various transgenic lines characterised. At the end of the project we had generated a range of lines and shown that HUB37 was the target for post-transcriptional degradation by bacterial effects. Our data predicts that bacterial effectors function to remove a negative regulator of plant immunity to promote disease.