Do parasitic weeds ‘hijack’ host hormone pathways to regulate the parasite infection process and the subsequent ‘reprogramming’ of host development?

Background: Striga species are obligate root parasitic weeds that infect rice, maize and sorghum (and some dicot crops) of sub Saharan Africa (SSA). They are the major biological constraint to crop production in SSA causing yield losses from 40 - 100%. Striga species infest over 70M h of land and directly affect the lives of over 100 million of the poorest subsistence farmers; thus they impact food security within SSA and worldwide. Striga is difficult to control as its lifecycle is intimately linked to that of its host pre and post attachment. Striga seeds germinate in response to specific chemical cues (strigolactones) present in host root exudates. Upon contact with the host root the Striga radicle forms an attachment organ the haustorium. The parasite then penetrates between the epidermal, cortical and endodermal cells of the host root in a manner analogous to that of an emerging lateral root. As the parasite cells reach the host xylem vessels a remarkable reprogramming of host cell differentiation occurs resulting in fusion of parasite and host xylem vessels thus allowing the parasite access to host nutrients. Within days 2-3 days the architecture of the host root and shoot are visibly altered: the host stem becomes stunted and in rice tiller emergence is suppressed and the crown roots are shorter in comparison to control plants. Recent work in the Scholes’ laboratory using rice and Arabidopsis as model hosts suggests that the plant hormones auxin and strigolactones are critical regulators of both the parasite infection process and the subsequent ‘reprogramming’ of host development.
The aim of this studentship is to test the hypotheses that (a) Striga ‘hijacks’ the lateral root auxin signalling pathways to successfully invade the root and (b) that changes in host root and shoot architecture result from alterations in auxin and/or strigolactone biosynthetic, transport or signalling pathways. The student will take a range of genetic, molecular, biochemical and bio-imaging approaches to address these hypotheses including infection of rice and Arabidopsis mutants (with lesions in auxin and strigolactone biosynthetic and signalling pathways) and plants containing promoter-reporter fusions to localise changes in gene expression. These experiments will be complimented by quantitative measurements of gene expression using qRT-PCR and measurements of auxins and strigolactones using mass spectrometry.
The student will be enrolled in the Doctoral Development Programme (DPP) at the University of Sheffield which provides research students with a range of skills and competency-based training opportunities orientated both towards their specific programme of study and towards future employment. Prof Scholes has an active research group and holds weekly meetings where all members of the lab report on their research or discuss journal articles. Prof Scholes holds regular one-on-one meetings with all PhD students to monitor progress and discuss individual projects. The student will also benefit from regular interaction with Prof Kepinski’s research group in Leeds through regular visits and via Skype.
This studentship is part of a White Rose studentship network on ‘Biotic constraints to crop production: biochemical and molecular basis of plant interactions with pests, parasites and symbionts’.

WHITE ROSE STUDENTSHIP NETWORK: Biotic constraints to crop production: biochemical and molecular basis of plant interactions with pests, parasites and symbionts.
The focus of this network of 3 studentships is an understanding the biotic interactions which impact on crop production at the biochemical and molecular level. Crops are subject to a range of pest attacks, often simultaneously, both above- and below-ground. Such pest outbreaks are predicted to increase under future climate change scenarios, though the mechanisms by which attack by one pest undermines or strengthens resistance to another remain poorly characterised in many cases. Arbuscular mycorrhizal (AM) associations also alter plant responses to pests, but again the molecular and biochemical changes underpinning these effects have seldom been investigated. Parasitic weeds such as Striga are another major constraint to crop production as they alter alter plant development, resource allocation and ultimately yield, although mechanisms underlying such alterations remain to be elucidated. The overlapping interests and complementary specialisms of the collaborators in this network will lead to synergistic novel advances in our understanding of plant interactions with organisms which may threaten or enhance crop production.

For more information about how to apply, or the application process, please contact Mrs S Carter (s.a.carter@sheffield.ac.uk).

To apply now go to: http://www.sheffield.ac.uk/postgraduate/online