Soil:plant signalling networks: manipulations to sustain plant productivity during drought

This project assesses the importance of long distance chemical signalling in the control of leaf growth in drying soil. It is argued that both soil to root signalling and root to shoot signalling will be important components of the process controlling vegetative growth in dryland agriculture. It will be important to understand both signalling processes if we are to manipulate plants to sustain productivity under environmental stress. The project is relevant to Sustainable Agricultural Systems since limitation of water use (rain-fed agriculture and/or deficit irrigation) is a crucial goal in many parts of the world, including UK. At the same time, we know that soil drying can greatly restrict plant production. We propose a combination of agronomic techniques (partial rootzone drying, the use of plant growth regulating bacteria) with genetic manipulation (reduced ethylene production under stress, reduced ethylene sensitivity) to overcome both hydraulic and chemical limitation to vegetative growth under drought stress or under deficit irrigation. We will assess the nature and significance of ACC and ABA signalling between soil and roots and between roots and shoots and use a model bacterial system to investigate the potential impact of soil organisms in the regulation of plant functioning in dryland environments. Investigation of this integrated system can provide a novel means of manipulating plant growth under stress on a commercial scale

We plan an innovative approach to increase understanding of the soil plant system with respect to growth of plants in water-limited environments. We seek to understand the role of long-distance chemical signalling in the regulation of plant growth in drying soil. The hypothesis is that an understanding of both soil to root signalling and root to shoot signalling will be necessary if we are to modify plant growth and functioning in drying soil. We will: a) determine whether plant growth promoting rhizobacteria containing the enzyme ACC deaminase can provide a low-technology solution to enhancing root and shoot growth of plants growing in drying soil. (Ethylene accumulation may greatly limit plant productivity under stress), b) understand the factors that determine ACC and ABA accumulation in the soil, as these soil signals will impact on the root to shoot signalling processes affecting shoot growth and functioning. This may particularly be the case in drying soil. c) elucidate the transmission of an ACC signal from roots to shoots using reciprocally grafted transgenic plants altered in ACC status d) compare two different strategies for genetically modifying plant ethylene response to soil drying (modification of ethylene synthesis versus ethylene sensitivity) under conditions simulating dryland agriculture and irrigated agriculture (partial rootzone drying). (Our hypothesis is that partial rootzone drying will promote signalling from roots to shots to restrict transpiration and maintain shoot water balance. This will allow us to see the full potential of overcoming ethylene limitation of shoot growth) e) compare genetic (manipulation of ethylene sensitivity) and agronomic (rhizobacterial inoculation) approaches to prevent the limitation of leaf growth by soil drying. The project should provide novel information on the signalling pathways between plants and soil and inform the management of the soil plant system in agriculture when water is less than freely available.