Regulation of root growth under osmotic stress conditions: a systems study

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Increasing food security for a growing global population is a major challenge facing humanity. Modulation of root system architecture is a key feature of plant responses to drought, potentially leading to yield benefits. Understanding the mechanisms regulating root development under drought conditions is therefore an important question for plant biology and world agriculture.Previously, by combining molecular biology (our experimental data and the data in the literature) with systems biology (network construction and spatiotemporal modelling), we have constructed a network describing the interactions between auxin, ethylene, cytokinin and the POLARIS peptide (required for correct auxin, ethylene and cytokinin signalling in Arabidopsis), revealing a hormonal crosstalk circuit that regulates root growth. This model has been expanded to include auxin transport via the PIN-FORMED (PIN) efflux transporters and has been implemented into a spatiotemporal model, which can reproduce the patterning of various hormones and response genes. In addition, we examined the effect of osmotic stress on ABA, cytokinin and ethylene responses and how they mediate auxin transport, distribution and root growth through effects on PIN proteins. We showed that under osmotic stress, Arabidopsis plants display increased ABA responses, and demonstrated the effects on auxin transport to the primary root meristem through altered PIN1 levels. We then used this information to construct a new network to integrate the effects of osmotic stress and ABA with auxin, ethylene and cytokinin. This network developed novel insights into how an integrated system of ABA, auxin, ethylene and cytokinin is formed due to the repression of ethylene effects by ABA to limit auxin accumulation in the meristem, and brought new understanding to the control of root development under osmotic stress. The current project builds on our success in applying combined molecular and systems biology study and further explores the regulation of root development under osmotic stress conditions.The project focuses on the question "How does osmotic stress regulate the size of the root meristem". It will deliver rigorous training across a broad range of molecular and systems biology areas. It will develop skills in both molecular biology and systems biology. This includes all or some following skills: RNA extraction and cDNA synthesis; quantitative real-time polymerase chain reaction (qPCR); compound light microscopy; confocal laser scanning microscopy; living imaging system; image analysis; network construction; computer software; and various modelling techniques. An important feature of this project is to employ a combined molecular and systems biology study to explore the complexity in the regulation of root growth under osmotic stress.