Role of phytoplasma effector proteins in plant development and plant-insect interactions

Orlovskis, Zigmunds (2017) Role of phytoplasma effector proteins in plant development and plant-insect interactions. Doctoral thesis, University of Easr Anglia.

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Abstract

Phytoplasmas are insect-transmitted plant pathogenic bacteria that
dramatically alter plant development. Phytoplasma virulence protein (effector)
SAP54 mediates degradation of host MADS-box transcription factors (MTFs) via
26S proteasome shuttle protein RAD23 to abolish normal flower development
and produce leaf-like flowers (phyllody). Phyllodies are common symptoms in
phytoplasma-infected plants worldwide. Why do phytoplasmas degrade MTFs
and induce phyllody? Are changes in host plant morphology adaptive and benefit
phytoplasma spread? Because phytoplasmas rely on their insect (leafhopper)
vectors for transmission from plant to plant, I hypothesized that the vegetative
tissues of the leaf-like flowers render plants more attractive to the insect vectors
that will aid phytoplasma dispersal in nature.
I discovered that the induction of phyllody is genetically linked with
enhanced insect egg-laying preference on the infected plants that exhibit the leaflike
flower phenotype. However, SAP54 enhances insect colonisation of plants
independently from floral transition and the changes in plant morphology.
Interestingly, male leafhoppers are required for the preference of females to lay
eggs on SAP54 plants. Moreover, SAP54 suppresses insect induced plant
responses in sex-specific manner by selectively downregulating male-induced
defence and secondary metabolism pathways. Furthermore, I identified four
MTFs that are expressed in plant leaves and play important roles in egg-laying
preferences by leafhoppers and demonstrate sex-specific regulation by SAP54.
Taken together, phytoplasma effector SAP54 enhances insect vector
colonisation of plants by suppression of insect-induced plant responses
independent of developmental changes. This is likely to occur by targeting MTFs
– a conserved regulators of both plant development as well as plant defence
against herbivorous insects. In addition to developmental changes, degradation
of MTFs by SAP54 may result in modulation of male-induced plant responses to
attract female insects for egg-laying and aid phytoplasma spread in nature.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Katie Miller
Date Deposited: 06 Apr 2017 10:31
Last Modified: 06 Apr 2017 10:31
URI: https://ueaeprints.uea.ac.uk/id/eprint/63188
DOI:

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