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Investigating Host Defence Priming Against Crop Pests Using a Bacteria-Based Effector Delivery System

Primary Supervisor: Dr Andrew Beacham, Agriculture and Environment

Secondary supervisor: Dr Joe Roberts (HAU), Dr Tom Pope (HAU)

PhD project title: Investigating Host Defence Priming Against Crop Pests Using a Bacteria-Based Effector Delivery System

University of Registration: Harper Adams University

Project outline:

Aphids are some of the most serious crop pests, inflicting direct damage through sap-feeding and acting as vectors for a wide range of plant viruses. The polyphagous peach-potato aphid, Myzus persicae, has a particularly wide host range and can cause dramatic yield losses in a number of crops including oilseed rape, potato, sugar beet and vegetables. Furthermore, M. persicae acts as a vector for over 100 viruses including potato virus Y (PVY), potato leaf roll virus (PLRV) and turnip yellows virus (TuYV) amongst others.

Recently it has been demonstrated that the delivery of plant elicitor peptides by bacteria can be used to enhance host plant resistance. Pre-treatment of potato roots with Bacillus subtilis expressing the potato elicitor StPep1 exhibited enhanced resistance to the root-knot nematode Meloidogyne chitwoodi (Zhang and Gleason, 2020). However, to our knowledge, such an approach has not been employed with aphid effector proteins and could represent a route to a novel means of aphid control by priming host defence responses to increase resistance. Such an approach would be timely regarding the increasing withdrawal of approval for traditional synthetic chemical control measures for aphids and development of insecticide-resistant aphid populations.

Sap-feeding insects such as M. persicae secrete effectors via their saliva in order to modify host physiology. Functional genomics studies have identified candidate M. persicae effector sequences (Bos et al., 2010). Transient overexpression of such effectors in Nicotiana revealed that selected effector candidates (Mp10 and Mp42) were able to reduce aphid fecundity and confer resistance to recombinant effector-carrying Potato virus X.

This project will determine the efficacy of host defence response activation and resistance establishment using aphid saliva effector delivery via bacteria.

Project outline:

  • Use the available persicae effector gene sequences to clone His-tagged Mp10 and Mp42 elicitors into bacteria (B. subtilis) using the published methodology of Zhang and Gleason (2020).
  • Investigate and optimise the efficacy of effector-expressing subtilis application methods on host plants (potato and oilseed rape) vs M. persicae lifecycle and behaviour (e.g. fecundity, generation time and feeding duration).
  • Insect herbivory causes changes in host plant volatile organic compound (VOC) profiles. The project will compare host VOC profiles in untreated plants with those treated with aphid effectors. Another possibility is to investigate associated aphid landing behaviour and foraging behaviour of natural enemies.
  • Mp10, but not Mp42, activates host defence jasmonate (JA) and salicylic acid (SA) signalling (Rodriguez et al., 2014). However, genetic analysis using aphid saliva leaf infiltration of Arabidopsis mutants suggested that saliva‚Äźinduced resistance against persicae is independent of the known defence signalling pathways in this species (De Vos and Jander, 2009). The hormonal pathways involved in the response to the saliva elicitor treatment will therefore be examined using targeted quantitative RT-PCR.
  • The effectiveness of recombinant subtilis application against a non-target pest, cabbage stem flea beetle (Psylliodes chrysocephala) will also be investigated.

References:

  1. Bos et al., (2010) PLoS Genet 6(11): e1001216. Zhang and Gleason, (2020) Nature Plants 6(6): 625-629. Drizou et al., (2018) Front Plant Sci 9: 1903. Rodriguez et al., (2014) Mol Plant Microbe Interact 27(1): 30-39. De Vos and Jander (2009) Plant Cell Environ 32(11): 1548-60.

BBSRC Strategic Research Priority: Sustainable Agriculture and Food: Plant and Crop Science

Techniques that will be undertaken during the project:

Polymerase chain reaction (PCR) and molecular cloning, microbiology, whole plant bioassays using pests, collection and analysis of plant VOCs using gas chromatography-mass spectrometry (GC-MS), electrophysiology for recording aphid feeding, RT-qPCR and plant hormone analysis.

In addition, masterclasses and mini-projects which will be available to the student will include: bioinformatics, programming statistical analysis using R, hydroponic culture, vertical and urban farming, integrated pest management and insect behavioural studies such as olfactometry.

Contact: Dr Andrew Beacham, Harper Adams University