The famous cereal 'green revolution' of the 1960s/1970s increased crop yields, averted famine and fed a growing world population. Green Revolution Varieties (GRVs) of rice and wheat were the genetic foundation of the green revolution. GRVs carry mutant growth regulatory genes that confer dwarfism, and this dwarfism increases yield because it reduces loss due to 'lodging' (flattening of plants by wind and rain), hence causing the yield increases of the green revolution. However, the mutant growth regulatory genes also cause GRVs to be less efficient in assimilating the nitrogen (N) supplied to them in the form of fertilizer. As a result, N that is not assimilated by GRVs is dissipated into the wider environment, where it causes severe damage to terrestrial and aquatic ecosystems, together with atmospheric greenhouse-gas pollution that precipitates climate change. Because today's high-yielding crop varieties still depend upon the mutant dwarfing genes for their high yields, it is necessary to find ways of developing new crop varieties that retain the benefits of GRV dwarfism but that are more efficient in their use of N fertilizers (have improved N use efficiency, NUE). Here we propose to exploit the rapid genetics and molecular biology of the genetic model Arabidopsis to make discoveries that will enable future enhancement of GRV NUE. The GRV dwarfing genes cause accumulation of a class of growth inhibitory proteins called DELLAs, and DELLAs also accumulate in the dwarf Arabidopsis GRV mutant model gai. Accumulated DELLAs inhibit the action of another class of regulatory proteins, the PIFs (or Phytochrome Interacting Factors). Our recent preliminary evidence from studies of Arabidopsis suggest that the inhibitory effect of DELLAs on PIFs may explain the reduced NUE of GRVs, and it is this novel and exciting finding that we exploit in this proposal. We will therefore first further test our working hypothesis that interactions between DELLAs and PIFs affect the assimilation of N: that the DELLAs accumulated in GRVs and gai oppose PIF function, thus reducing N assimilation. If this hypothesis is correct, modulation of the DELLA-PIF relationship may provide a novel route towards improving GRV NUE. We have the following objectives: A. Obtain an in-depth understanding of PIF-regulation of Arabidopsis and rice N assimilation - essentially performing genetic tests of the role of PIFs in regulation of N metabolism and assimilation in Arabidopsis and rice. B. Determine how the DELLA-PIF interaction regulates the abundance of mRNA encoding nitrate reductase (NR), a key enzyme in N assimilation - this an exploration of how the DELLA-PIF interaction controls the expression of the gene encoding that enzyme. C. Determine if the DELLA-PIF interaction also directly affects the abundance and/or specific enzymatic activity of the NR enzyme itself. D. Determine if NUE can be increased despite retaining yield-enhancing dwarfism. This is important because it could lead to the development of crops which retain the high yields of current GRVs, but at reduced environmental cost. First, we will determine if increasing PIF activity might confer such benefits. However, because increasing the activity of PIFs themselves in GRVs might have additional unwanted consequences, we will additionally explore other routes (downstream of PIFs) to improving GRV NUE whilst retaining yield-enhancing dwarfism. Inherent in our strategy is initial translation of findings from Arabidopsis model to crop (rice), exploiting our long-standing combined expertise in DELLA biology, model-crop translations, and whole genome sequence analysis. Our long-term aim (future proposals) is to use the fundamental understanding gained here in the development of rice and wheat GRVs having enhanced NUE, thus enhancing global food security and reducing agricultural environmental degradation.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

This Pump-Priming project will initiate a new collaboration with a leading Chinese research group (Prof Xinming Wang, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences). Our aim is to assess the importance of a new atmospheric reaction, recently discovered by the UK team through a current NERC research grant, using the unique simulation chamber facility available in Guangzhou. The wider project context is the atmospheric processing of sulphur species. Well understood atmospheric chemical processes break down the sulphur species - molecules such as dimethylsulphide (DMS) or SO2 - these reactions are driven by OH radicals in the gas phase, and form sulphate aerosol particles, which scatter sunlight and can catalyse the formation of cloud droplets - so the processing of sulphur species exerts a major influence upon climate. Sulphur processing leading to sulphuric acid also contributes to rainwater acidity. Our current NERC project aimed to investigate the impact of a new set of chemical reactants upon sulphur processing - the Stabilised Criegee Intermediates (SCIs). SCIs are formed from alkene-ozone reactions (found throughout the boundary layer) and alkyl iodide photolysis (in the marine boundary layer), and can act as atmospheric oxidants, like OH, initiating the processing of species such as SO2. Our current project was motivated by the recent discovery that the SCI + SO2 reaction was three orders of magnitude faster than previously thought - but SCI behaviour had not been tested under realistic atmospheric conditions. Our approach was to use the EUPHORE atmospheric simulation chamber (a 200 m3 reactor in Spain, in which an artificial atmosphere may be introduced - containing, for example, alkenes, ozone and SO2 - and fitted with instruments to monitor the evolving chemical composition). In EUPHORE, we have studied reactions of SCIs with SO2, H2O and their thermal decomposition - leading to five papers so far - and also discovered that SCIs, formed from isoprene-ozone reactions, react with DMS. DMS is the dominant natural sulphur emission (with volcanic SO2), so any enhancement in DMS oxidation (e.g. by SCIs, alongside OH) will increase the rate and change the spatial distribution of sulphate aerosol formation, of potentially substantial importance for atmospheric composition and climate. However, the instruments in EUPHORE could not determine the products of the SCI + DMS reaction; nor were we able to assess their dependence upon the alkene used to form the SCI. In this project, we propose to use the newly developed chamber in Guangzhou to resolve these uncertainties - the GIG chamber instrumentation can detect the gas- and condensed-phase DMS oxidation products, and has recently been used for a study of SCI chemistry in vehicle exhausts. The project will consist of PI / research staff exchanges to plan and model the chamber experiments in detail, followed by simulation chamber measurements to probe the SCI - DMS system in Guangzhou. These experiments will definitively determine the importance of this new reaction, under realistic atmospheric boundary layer conditions. This proposal has developed following discussions between Bloss and Wang at meetings in Beijing, and a visit by Bloss to the GIG facility in March 2015. In addition to the specific science goals, it will nurture a developing collaboration between UK groups (with substantial expertise in the conduct of simulation chamber experiments) and leading Chinese researchers at GIG (with unique chamber facilities) in atmospheric chemistry, with potential for future links, for example in the context of forthcoming NERC-Newton-NSFC "Urban Air Pollution in a Chinese Megacity" projects. China is rapidly emerging as a research-leading nation, and this engagement links to top scientists (i.e., within the Chinese Academy of Sciences) thereby supporting the UK's international reputation in atmospheric science.