Improving rice yields - Woolhouse lecture

31 October 2016 - By: Caroline Wood

Improving rice yields

Rice terraces in Banaue
Rice terraces in Banaue, Phillipines. Photo: Jane Langdale


The Woolhouse lecture – now a traditional event at the SEB Annual Meeting - pays tribute to the remarkable botanist and plant physiologist Harold Woolhouse (1932-1996). A former influential president of SEB, Harold was Director of the John Innes Centre between 1980 – 1989, transforming it into an international centre of excellence for the plant sciences. Each year, the SEB invites one of the modern generation of plant pioneers to describe how their work is pushing the frontiers of knowledge and technology even further. At SEB Brighton 2016, Jane Langdale (Professor at the University of Oxford) introduced us to exciting research aimed at improving rice yields. 


As rice provides 30% of the calorie intake in Asia, this crop will have a pivotal role in feeding growing populations. “Rice is one of the few crops where the people who grow it eat it themselves, rather than exporting it or using it for animal feed,” Jane said. Rice yields have plateaued in recent years, with production only increasing by <1% each year between 2000-20101. Last year, demand in Asia outstripped production, forcing countries to dip into their reserves. Clearly a breakthrough is needed to boost the growth in yields. 

Carbon Conversion

One solution could be to introduce C4 photosynthesis into rice. In standard C3 photosynthesis, the activity of the key carbon-fixing RuBisCO enzyme is limited by the presence of oxygen, which causes the competitive reaction of photorespiration. C4 plants, however, have a distinct ‘Kranz’ anatomy (from the German for ‘wreath’) that enables the concentration of CO2 around RuBisCO. The leaf veins are surrounded by a concentric layer of bundle sheath cells, with an outer layer of mesophyll cells. In the mesophyll cells, CO2 is fixed into a 4-carbon intermediate (by an oxygen insensitive enzyme) which is then shuttled to RuBisCO in the bundle sheath cells. This prevents CO2 from being effectively lost through photorespiration, allowing more to be fixed into carbohydrate. Because C4 plants also have higher water- and nitrogen-use efficiencies, it is thought that “introducing C4 photosynthesis into rice could increase yields by 50%,” said Jane.

Projecting ahead

This is the goal of the C4 Rice Project, a global consortium that was brought together by the International Rice Research Institute (IRRI), and is funded by the Bill & Melinda Gates Foundation – currently through a grant to the University of Oxford with Jane as lead investigator. This ambitious task would require both introducing Kranz anatomy into rice and spatially compartmentalizing photosynthetic enzymes between bundle sheath and mesophyll cells. “Kranz anatomy has evolved over 60 times independently across diverse plant families so it shouldn’t be that difficult,” mused Jane. So far, her own work has focused on identifying gene candidates to develop a ‘molecular toolbox’ for introducing Kranz anatomy. Maize is an ideal model system for this, as the husk leaves that surround the ear have a C3 anatomy whereas the foliar leaves have the C4 Kranz arrangement. “We compared transcriptome profiles between husk and foliar leaves at the time when Kranz anatomy develops,” said Jane. This identified approximately 20 gene candidates which are now being expressed in rice to assess phenotypic consequences. “We are currently at the stage of stacking up to five transgenes at a time, but we don’t anticipate any breeding trials until 2029,” she concluded. “We may have started this but the people who will deliver it will be our young PhDs and postdocs”.

As one who believed that applying scientific research was the solution to feeding the world, Harold Woolhouse would surely have approved. 

For more information on the C4 rice project, visit http://www.c4rice.com

References

1. Khush, G.S. (2013) Strategies for increasing the yield potential of cereals: case of rice as an example. Plant Breeding, vol. 132, pp 433-436.

 

Category: Plant Biology
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Caroline Wood

Caroline Wood was the SEB’s 2014 science communication intern. Since then, Caroline has been a regular contributor the SEB, reporting on events and writing insightful features for our members.
Caroline has an undergraduate degree from Durham University in Cell Biology and is currently a PHD student at Sheffield University studying parasitic Striga weeds that infect food crops. You can read her blog here.