Dynamics of Phytoplasma Effector Interactions with Plant TCP Transcription Factor (sub)classes

Capdevielle, Sylvain (2019) Dynamics of Phytoplasma Effector Interactions with Plant TCP Transcription Factor (sub)classes. Doctoral thesis, University of East Anglia.

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Phytoplasmas are bacterial plant pathogens vectored by sap-feeding leafhoppers. These bacteria induce dramatic changes in plant development, such as witches’ brooms and secrete effectors that modulate host plant processes. Aster Yellows phytoplasma strain Witches Broom (AY-WB) secretes the effector Secreted AY-WB Protein 11 (SAP11), which binds and destabilizes plant TCP (TEOSINTE BRANCHED1, CYCLOIDEA, PROLIFERATING CELL FACTORS 1 and 2) transcription factors, particularly members of the class II TCPs of the CYCLOIDEA/TEOSINTE BRANCHED 1 (CYC/TB1) and CINCINNATA (CIN)-TCP (sub)classes. Stable production of SAP11AYWB in A. thaliana and maize leads to the induction of specific developmental phenotypes, such as witches’ brooms and altered leaf shapes, consistent with the destabilisation of Class II CYC/TB1 and CIN-TCPs. SAP11 effector homologs were found in other phytoplasmas, but their binding specificities toward the TCP (sub)classes are unclear. This thesis shows that four divergent SAP11 effector homologs from various phytoplasma groups differentially bind class II TCP (sub)classes, specifically the helix-loop-helix motif of the conserved TCP domain. I extended the analysis to include SAP11 homologs from divergent phytoplasma groups and investigated their phylogeny. I showed that the SAP11 proteins group in five distinct clades. The SAP11 phylogeny is different from the phytoplasma 16S rDNA phylogeny, suggesting horizontal exchange of SAP11 genes among phytoplasmas. Interestingly, the SAP11 effector homologs within each clade bind TCP members from three TCP (sub)classes, including class I TCPs. I elucidated the SAP11 region involved in the binding specificities toward class I and class II TCPs. Finally, SAP effectors of AY-WB phytoplasma genes that lie on the genetic island of SAP11AYWB also interact with TCP (sub)classes, including Class I TCPs, thereby expanding the interaction range of AY-WB SAPs to all TCP (sub)classes. The work enables predictions of binding specificities to TCP (sub)classes of SAP11 effector homologs that may be discovered in the future.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 11 Feb 2021 14:40
Last Modified: 11 Feb 2021 14:40
URI: https://ueaeprints.uea.ac.uk/id/eprint/79224


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