Rice Research Newton Fund: Exploiting a Cyanobacterial CO2 Concentrating Mechanism to Increase Photosynthesis and Yield in Rice

Food security is internationally recognised as one of the major global challenges of the 21st century. By 2050, it is predicted that world food production will have to increase by 50% to meet demand. This is against the pressures of global climate change and resource limitations. Meeting this challenge is going to require the development of innovative strategies to make use of our unprecedented knowledge of modern bioscience in the post genomic era. Since rice is the most important human food, consumed by more than half of the world's population, developing new highly-productive rice varieties will be fundamental to meeting the 2050 goal.

Whilst substantial gains in rice yield have been obtained by traditional breeding, achievement of major increases in the future will require novel approaches. Improved photosynthesis has been identified as a major target for bioengineering for enhanced yield of C3 crop plants. Improving photosynthetic efficiency does not simply increase the amount of carbohydrate produced per hectare of land, but it also increases the amount produced per unit of water and per unit of nitrogen. This means not only environmental sustainability, but also higher income and better food security for small farmers.

The properties of the carbon-fixing enzyme Rubisco (ribulose-1:5-bisphosphate carboxylase/oxygenase) are known to limit the efficiency of photosynthesis in land plants. Rubisco catalyses the combination of RuBP (ribulose-1,5-bisphophate) with CO2, but also catalyses the reaction of RuBP with oxygen, leading to photorespiration, a process in which NH3 and previously fixed CO2 are lost. Some land plants (C4 plants) and bacteria have evolved mechanisms that concentrate CO2 near Rubisco and thereby both increase photosynthetic CO2 assimilation and decrease the competing wasteful reaction with oxygen. However, rice lacks this ability. As a result, rice utilizes a Rubisco enzyme that has higher CO2 affinity but is slower than Rubisco enzymes in plants with carbon-concentrating mechanisms such as maize. Consequently, the plants must devote considerable amounts of protein, and thereby, nitrogen, to allow Rubisco to carry out adequate carbon fixation, reducing yield and biomass production. Replacing endogenous Rubisco with a faster enzyme with less CO2 specificity, along with a carbon concentrating mechanism (CCM), could significantly improve CO2 fixation, according to published models.

We propose to engineer the nuclear genome of rice to express components of the cyanobacterial beta-carboxysome, including a faster Rubisco enzyme. We will identify transgenic lines of rice with the required levels of carboxysome shell proteins, internal proteins, and cyanobacterial Rubisco, which can then be crossed to express all of the novel proteins in the same line. , we will install a combination of bicarbonate transporters in order to supply CO2 to the engineered carboxysome. Finally we will also reduce the expression of the chloroplast stromal carbonic anhydrase and endogenous rice Rubisco through RNA silencing technology Based on promising results with the model plant tobacco, we believe it is time for forge ahead with a project that could bring the cyanobacterial CCM into rice for the future.

Our proposed research project focuses on enhancing photosynthetic efficiency and capacity to substantially increase yield in rice. The proposed research is transformational; although high risk, it has the potential to deliver enormous gains in terms of increased rice yields using an approach that has not previously been utilised in breeding programmes. Modelling studies indicate that a functional CCM in a C3 plant such as rice could result in increase in yield of 36-60% (McGrath and Long, 2014a). The project builds on earlier (but now ended) investments by BBSRC.

Communications and Engagement
Outcomes of the project will be disseminated to the wider scientific community and beyond, through a number of means. Findings will be published in high ranking peer reviewed journals. To reach a broader scientific audience all partners regularly engage in publication of widely read review articles. In addition, the PIs and PDRAs will present their work at international conferences.
The project team will engage with a wide range of audiences (public, policy makers, farmers, and academics). These engagements will encompass wider social issues such as GM and food security as well as the details of the project. In addition, the applicants regularly engage in outreach activities such as visiting schools, organising public open days and providing materials and participation in summer schools.

Collaborations
It is highly possible that direct industrial collaborations will occur during the timeframe of this project. We will identify outputs with potential impact by discussion of the research with industrial contacts. We will also fully engage (visits and correspondence) with national and international agencies working to increase rice yields.

Capability
The PI's have relevant experience and a track record in public dissemination of research findings. Any publicity activities will be coordinated through the Science Communication offices in both host organisations.

Exploitation and Application
Potential intellectual property will be identified and properly protected through the commercialisation offices of both universities. Non-patentable findings will be disseminated to the scientific community through conference presentations and peer-reviewed publications and to the wider public through the media, national and local events.
Material Transfer Agreements will be arranged between the partners in this proposal to safeguard ownership and rights of the research organisations involved, liabilities, and to cover any IP arising. This also covers other important aspects of working together such as acknowledgement of the source of the materials in any publication, provision of raw data, reports or publications or inventions relating to the materials and arising from the specific research programme. The agreement also requires subsequent discussion of any intellectual property arising, and negotiation on how it should be exploited, with what division of work related to its exploitation and the revenues between the partners. The supplier of materials will retain the right to use an Invention for non-commercial research purposes. The PIs have relevant experience and track record in filling patents and in public dissemination of research findings.

Training
The proposed research will provide advanced training in both China and the UK.