World food demand is predicted to double by 2050. Meeting this demand is a major global challenge, and requires increased crop yields at minimal environmental cost. Present-day high-yielding 'green revolution crop varieties' (GRVs) are inefficient in their use of nitrogen (N) fertiliser, an inefficiency that is costly to the farmer and damaging to the environment. The world needs new crops that are both higher yielding and have increased N use efficiency (NUE). Our project fuses distinct UK/China expertise to improve rice NUE. It retains the outstanding features of current rice GRVs, and transforms them into Super-Rice varieties that are high yielding and have enhanced NUE. Using a pioneering approach combining the discovery of natural genetic variants with marker-assisted breeding and 'genome editing', we will create Super-Rice that will be high-yielding when grown with reduced N fertiliser inputs. First, WPs1-3 exploit a variety of genetic, genomic and bioinformatics techniques to discover individual genetic variants that increase the NUE of rice GRVs. WP1 discovers the molecular identities of variant genes increasing NUE in the field. WP2 focusses on variants of the developmental regulatory genes that play overarching roles in controlling the growth and metabolism of plants. There is important precedent for exploiting such regulatory variation, because the initial GRVs themselves were created by use of such variants. WP3 focusses on the discovery of variants increasing the activity of the transporters that enable rice to extract N from the soil. However, the variants discovered in WPs1-3 may come from wild or other strains of rice that are not themselves GRVs. WPs1-3 therefore importantly use the new technique of genome-editing to specifically determine if these new variants increase NUE in GRV genetic backgrounds. Genome-editing enables precise alteration of genome sequence, thus enabling us to edit specific GRV gene sequences (change them into the newly discovered variant form). The yield of these genome-edited GRVs will then be measured in low-N soils, thus telling us if the newly discovered variant can indeed increase the NUE of the GRV. Next, WP4 further exploits the ability of genome editing to simultaneously edit more than one genomic location. This enables the combined ('stacked') introduction of multiple variants into one GRV. It is possible that variant combinations will generate NUE increases that are at least additive (a simple sum of individual variant effects) and that may be synergistic (increases that are greater than the simple sum effects of individual variants). Thus, in WP4, we will combine ('stack') multiple selected variants into Super-Rice genotypes, and then determine the yields of these Super-Rice genotypes in low-N soils. Our genome-edited Super-Rice will not contain any 'foreign' transgenes, and may therefore more readily receive regulatory approval for agricultural use than will transgenic 'GM' varieties. However, because full adoption of Super-Rice requires general public acceptance, we will also pioneer the use of genome-edited Super-Rice to enhance the efficiency, focus and speed of conventional marker-assisted breeding of Super-Rice. Genome-edited Super-Rice will guide plant breeders in the development of (non-genome-edited) Super-Rice that will be bred using natural rice variants and that will be publicly acceptable because it is neither GM nor genome-edited. The promotion of bilateral UK-China rice research relationships is another major objective of our proposal. We build upon and sustain pre-existing partnerships (XF and NPH; XF and QQ), and derive added value from a new one (NPH and QQ). In summary, we propose a transnational UK-China partnership that will breed publicly acceptable enhanced-NUE Super-Rice that will enhance the sustainability of Chinese and world agriculture and help feed the world in the years leading up to 2050 and beyond.