Environmental and genetic determinants of Brassica crop damage by the agricultural pest Diamondback moth

Project Rationale
The diamondback moth (DBM), Plutella xylostella, is an agricultural pest with worldwide impact on brassica crops (>$5 billion in annual damages). Its unique glucosinolate sulfatase (GSS) enzymes allow it to specialize on cruciferous host plants by evading their glucosinolate/myrosinase defence system1. In preliminary studies, we established that herbivory by DBM caterpillars is controlled both by environmental light and their internal daily timekeeping systems. Moreover, the expression of DBM GSS genes exhibits circadian rhythmicity. This project aims to elucidate abiotic and biological determinants of DBM herbivory of its host plants. It will complement ongoing research focused on circadian control of herbivory in the DBM caterpillar by concentrating on environmentally-controlled defence mechanisms in cruciferous plants (Brassica rapa and Arabidopsis thaliana). The following Specific Objectives will be pursued:
SO1) Identify how host plant glucosinolate production and herbivory by DBM are affected by (a) glucosinolate biosynthesis and daily timekeeping in the host plant, (b) daily environmental cycles in light and temperature. The latter will simulate representative light/temperature cycles for the UK and explicitly explore the predicted impact of light pollution and global warming.
SO2) Identify changes in plant and DBM expression profiles that are closely associated with changes in herbivory across different environmental contexts.

Methodology
This Doctoral dissertation project involves: (i) culture of both DBM as well as chinese leaf cabbage (Brassica rapa) and various wild-type and mutant lines of Arabidopsis thaliana; (ii) DBM herbivory assays on these plants (using time lapse imaging and quantitation of leaf tissue lost and caterpillar weight gained); (iii) extraction and chromatographic quantification of glucosinolates from plant tissue samples; (iv) real-time quantitative PCR analysis of transcript profiles in both DBM caterpillars and host plants and (v) bioinformatics and statistical data analysis. Experiments will make use of the model cruciferous plant Arabidopsis thaliana to identify genetic determinants of DBM herbivory by employing mutants that impact daily timekeeping and/or glucosinolate biosynthesis2 (SO1a). The student will also follow up on the observation that glucosinolate production is restricted during short days3 and test how short photoperiods and associated temperature profiles affect glucosinolate levels and herbivory (SO1b). qRT-PCR analyses of both DBM caterpillars and host plants will be conducted for conditions known to impact glucosinolate levels and/or herbivory to identify associated changes in gene expression. The project will also be informed by citizen scientist monitoring of the context of DBM sightings.

Training
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Biological Sciences as well as at the CASE partner organisation (Royal Horticultural Society in Wisley). Specific training will include: items (i-v) listed under Methodology as well as oral and written presentation skills, attendance of national and international research conferences and participation in outreach and engagement activities.