Underground power struggles: how does silicon tip the balance between mutualistic and pathogenic root fungi?

Sustainable agricultural systems with reduced application of fertilisers and chemicals involved in pest control is a long term objective for UK agriculture. Yet, there is evidence that soil health is declining under current agricultural practises and this decline may be further exasperated as chemical applications are reduced. Moreover, outbreaks of pests and pathogens are also predicted to increase under future climate change scenarios. Consequently, the interactions between plant roots and soil microbial groups will become increasingly important if food security is to be achieved.

Two key groups of soil microorganisms are that of the arbuscular mycorrhizal fungi (AMF) and plant pathogens. AMF form a symbiotic relationship with the majority of land plants including most agriculturally important crop species, and may confer a number of benefits to their host plant including enhanced uptake of nutrients, improved water relations and increased resistance to pathogens. The exact mechanisms by which AMF improve pathogen resistance however are poorly understood but may include physical exclusion, improved plant nutrient status and enhanced plant defence status. Plants also increase levels of silicon (Si) uptake under stressed conditions including when under pathogen attack. While it has been established that in foliar tissues Si can protect against pathogen attack through 1) being deposited on the surface thus reducing fungal hyphal penetration and 2) through a stimulation of plant defence signalling pathways, little is known about how AMF colonisation may be affected although there is some evidence that AMF may actually enhance plant acquisition of Si.

This project will examine the impact of AMF-pathogen interactions on Si-uptake and signalling pathways in the agriculturally important crop, barley. We will determine to what extent plant uptake of Si is influenced by AMF colonisation and fungal pathogen attack and if spatial (i.e. by varying distance from the root surface into the rhizosphere) and temporal differences in exposure of these two key microbial groups influence the susceptibility of the plant to disease. We will also follow large-scale transcriptional reprogramming mediated by plant gene regulatory networks. Such networks enable plants to fine-tune their responses to their environment. We will determine how these gene regulatory networks controlling barley response to pathogen infection are altered by the presence of silicon and/or AMF. Identifying key control points within these networks highlights candidates for targeted approaches to crop improvement and to help to achieve the long term goal of ensuring global food security through improved soil health.