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Title: Role of phytoplasma effector proteins in plant development and plant-insect interactions
Author: Orlovskis, Zigmunds
ISNI:       0000 0004 6059 9553
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2017
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available