The role of pathogen effector proteins in altering host plant transcription

Doctoral thesis English OPEN
Tetlow, Mary Louise
  • Subject: QR
    mesheuropmc: food and beverages | fungi

Plant pathogens secrete effector proteins in order to overcome immunity in plants stimulated by common microbial patterns. The genomes of oomycete pathogens including Hyaloperonospora arabidopsidis (Hpa) are predicted to contain a large number of effectors. These experiments focussed on characterising an interaction between predicted Hpa effector HaRxL14 and Arabidopsis protein phosphatase type-2CA (PP2CA), which functions as a co-receptor in response to the phytohormone abscisic acid (ABA). This interaction was previously identified in a yeast two-hybrid screen. Bimolecular fluorescence complementation experiments verified an interaction in the nucleus. Over-expression of the effector in planta enhances susceptibility of Arabidopsis to Hpa, although knocking-out PP2CA in the host did not have a clear effect on infection. Furthermore, a potential role for the interaction in enhancing host signalling associated with ABA was highlighted from microarray analysis of Arabidopsis lines over-expressing the effector. The up-regulation of various ABA-related genes supports previous findings that ABA may disrupt host response to biotrophic pathogens.\ud \ud Furthermore, it was hypothesised that phytohormones including jasmonic acid (JA), ABA, and salicylic acid (SA) could have a role in coordinating host transcription at the level of chromosome conformation. Progress was made towards optimising a method for use with Arabidopsis related to chromosome conformation capture (3C). These experiments began to examine the spatial interactions of JA-induced genes in Arabidopsis. This method could be used to determine if related genes co-localise at specialised transcription factories. These transcription factories have previously been studied in other models including mammals, although their potential role in plants is currently not well understood. Overall, a Hpa effector was shown to interact with host protein PP2CA potentially to up-regulate ABA-related genes. It remains to be established if phytohormones have a role in coordinating transcription through manipulating spatial interactions of genes.
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