Plant growth responses to the environment: interfaces between anti-oxidants PARP and the cell cycle

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Even in the relatively benign climate of the UK, environmental stresses are of major significance to the farmer and grower, not only through their impact on overall yield, but also the consequential year-on-year uncertainties in overall harvest. The stresses of particular importance in the UK are drought, high temperature and atmospheric pollution. Current climatic conditions will become both less optimal for growth of primary UK crops and more uncertain, as temperatures rise, summer precipitation declines and predictability decreases. Globally the problem is even more significant. Hence abiotic stress already has a major impact on crop yields, significantly through the cessation of growth under conditions of mild stress. Growth arrest arises from a cessation of cell division in meristems, and recent work shows clearly that the cell cycle stops in G1 phase in response to changes in anti-oxidant pools (specifically glutathione [GSH] and ascorbate [AA]), which themselves are a measure of abiotic stress. A further link between abiotic stress and the cell cycle is suggested by the finding that downregulation of the enzyme poly(ADP-ribose) polymerase (PARP) gives significantly enhanced stress tolerance. The same enzyme links cell cycle and stress in animals. This project will combine the expertise and know-how in AA and GSH synthesis and metabolism and whole plant physiology at Rothamsted with that of the Cambridge laboratory in cell cycle regulation and microarrays to elucidate and characterise the components that regulate cell cycle progression in response to modulations of GSH, AA and PARP and to extend this by identifying components that link abiotic stress to plant growth. We wish to understand the specific interfaces between these pools and activities and the cell cycle, and to further analyse the role and mode of action of PARP in conferring stress tolerance. The collaboration is essential for the success of the research programme as it exploits the unique toolsets available between the Rothamsted and Cambridge labs. This includes mutants with altered glutathione or ascorbic acid metabolism, multiple antiobodies, CycD::GUS reporter lines, transgenic plants lines with altered expression of cell cycle components, Arabidopsis cell lines that have the capacity for synchronisation and an extensive and growing set of bioinformatic data on gene expression and protein profiling in the same cell line. The project follows three broad phases of work which are integrated between the two labs: (1) Characterisation of the effects of GSH, AA and PARP levels on cell division in the Arabidopsis suspension culture and identification of core cycle genes modulated by GSH and or AA and or PARP. Importantly the approaches will utilise transgenic manipulation of enzyme activities as well as chemical inhibitors. Cell cycle analysis will focus on cyclin D genes as the ultimate regulators of the commitment to cell division. (2) Identification of global changes in gene expression resulting from changes in GSH, AA and PARP levels, with specific focus on genes that could act as potential upstream regulators of cell cycle genes in mediating GSH, AA and PARP control of cell division. (3) Further analysis of the candidate upstream genes to confirm that they are involved in controlling cell cycle entry in response to GSH, AA and PARP levels. Joint with BB/C515047/1