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Festival of Plants Public Talk: Can we improve crop photosynthesis to feed the world sustainably?

Lack of access to adequate food today causes many more deaths than malaria, AIDS and TB, and is expected to become worse. Ensuring the world can feed itself without having to destroy more rainforest and other natural habitats, is going to require a new generation of plant scientists able to translate the massive advances made in molecular understanding to new highly efficient food crop varieties.

Steve Long FRS is a Gutgesell Endowed University of Illinois Professor of Crop Sciences and Distinguished Professor of Crop Sciences at the University of Lancaster, UK

Festival of Plants 2017 Cambridge University Botanic Garden held its annual Festival of Plants, Saturday 18 May 2016 offering something for everyone to enjoy: from families to photographers, gardeners to budding plant scientists or anyone looking for an interesting day out in beautiful surroundings. This is a day dedicated to bringing plant into focus.

CambPlants Hub was delighted to host Professor Stephen Long for a public talk on improving photosynthesis for food security. Long began his talk by highlighting the key challenge ahead for sustainable agriculture. Rising global population especially in urban areas, aspiring appetites, will eventually require a more than 70% increase in food production by 2050, according to United Nation’s estimates. However, climate change, spread of plant pests and diseases alongside land degradation from current farming methods will constrain our ability to do so. It has become increasingly difficult to achieve yield increases in the field. Given that crop science research takes more than a decade to be translated into field outcomes, it is thus paramount to develop ways to enhance crop productivity today.

To this end, Long’s work aims to improve the photosynthesis for crop plants.

How can we improve photosynthesis?

Photosynthesis involves more than 160 steps with two key stages – harvesting energy from light and using it to convert carbon dioxide into sugars. Looking at the yield equation for photosynthesis, while the efficiencies of capturing incoming solar radiation, and of partitioning photosynthesis products into harvested plant parts have been maximised over decades of agricultural practice and research; the current efficiency of converting solar radiation into biomass is the furthest away from the theoretical maximum. Hence boosting photosynthesis, which has been improved little in crops and falls far short of its biological limit, will be one of the key ways forward to increase crop productivity and harvest yields.

Would rising carbon dioxide concentrations in the atmosphere then improve photosynthesis?

Through open air CO enrichment in fields to simulate future increases in concentration, yields of major crops increased – in soybean (16%), wheat (15%) and rice (12%). Yet at the same time, the amount of pest damage doubled, as they are also more active under higher CO concentrations. Engineering other methods to boost crop productivity, instead of relying on higher CO concentrations, will be needed.

Photosynthesis, with more than 160 steps, is not easy to optimise. To identify the key stages to tackle, Long and colleagues adopted a systems approach. Assisted by the fact that photosynthesis is known is more detail than any other plant process, they described each step with a non-linear differential equation. The emergence of high performance computing, that is the rapid growth of computational power and new software tools, has enabled complete photosynthetic kinetic models to be simulated and optimised. This, however gave billions of permutations. With a computer scientist working for NASA, they were able identify key bottlenecks in photosynthesis. Increasing the amounts of key enzymes (SBPase and FBP aldolase) in the Calvin cycle, for example, achieved significant yield increases over wild-type, untransformed tobacco plants – both in the lab, and in field experiments. Tobacco is the model crop plant of choice, because of the ease of transforming the plants also their ability to form close canopies in the field. Improvements first developed and achieved in tobacco can then be transferred into important crop plants such as rice, soybean and cassava. They have already shown that increased SbPase, predicted to be important from their computer model and demonstrated in tobacco, now also increases the productivity of soybean.

Another aspect highlighted by the model is the limiting effect of photoprotective mechanism, which could cost up to 20% of their potential yield. In full sunlight, photoprotection is required to dissipate excess light energy as heat, as otherwise the oxidative damage will affect the photosynthetic and cellular machinery. However, when shaded by clouds or other leaves, photoprotection still persists for a while, limiting photosynthesis as a result. Accelerating the recovery process by changing three genes, Long and colleagues managed to increase CO uptake and dry biomass by around 15%. As photoprotection is common to all plants, this breakthrough in November 2016 received substantial attention and publicity for its immense potential to be applied for future yield improvements. Nevertheless, several challenges remain to be addressed – from transferring these changes to crop plants and overcoming regulations for transgenic crop plants. Still, it is a huge step forwards for crop science research and further proves that targeted, informed genetic manipulation of plants – be it to optimise photosynthesis or disease resistance, will be important for sustainable and productive agriculture.

CambPlants also participated in other activities as part of the Cambridge University Botanic Garden’s Festival of Plants. Researchers ran a series of interactive exhibits in the Pop up Science tent, including magnetic games, how to be a pollinator, computer modelling exercises and a ‘build your own plant’ activity.  Short informal talks in the Talking Plants tent were also given, and several other researchers explored the Garden with the public, exploring various areas of interest including leaf shapes and sizes and tropical plants.  A full programme for the Festival of Plants can be found here.

by Chiu Chai Hao

‘This lecture by Prof. Steven Long was both informative, important and relevant to the critical situation facing our expanding world population.’ Member of the audience