The International C₄ Rice Consortium has completed its first three years of research, the outcomes of which Professor Susanne von Caemmerer, a member of The Consortium and RSB’s Plant Science Division, has detailed in the 29 June 2012 edition of Science.

The Consortium is funded by the Bill and Melinda Gates Foundation and is is led by the International Rice Research Institute based in the Philippines, the largest non-profit rice research institute in the world. The team of researchers, which includes Professor von Caemmerer, has been assembled to maximise the potential of rice as a food crop, reducing poverty and hunger, and improving the health of rice consumers.

The enzyme Rubisco plays a central role in the life cycle of rice, converting sunlight and carbon dioxide (C0₂) into sugars to fuel growth in a process known as C₃ photosynthesis. Rubisco has long been known to be inefficient in this process; it requires a higher concentration of CO₂ than is available in today’s atmosphere, a relic from its evolution in a CO₂-rich atmosphere millions of years ago.

Some land plants have developed a way of overcoming Rubisco’s inefficiencies by adding another step to the photosynthesis process, concentrating CO₂ in specialised bundle sheath cells. In this process, known as C₄ photosynthesis, these CO₂ rich cells act like a time machine, allowing Rubisco to work in optimum CO₂ conditions - just like when it first evolved.

“In comparison with C₃ crops such as rice, C₄ crops such as maize and sorghum have higher yields and increased water- and nitrogen- use efficiency,” says von Caemmerer.

The C₄ Rice consortium has spent the past three years identifying the genes that are necessary for C₄ photosynthesis and has just received another three years funding from the Bill and Melinda Gates Foundation to continue with their work. The next steps are to incorporate these genes into the rice genome, hopefully resulting in new efficient breeds of rice.

“Leaves in C₄ plants have closer veins which helps achieve higher rates of photosynthesis and we have produced promising rice mutants that show reduced vein spacing, which is a good step in the right direction.

“C₄ photosynthesis has evolved independently over 60 times in nature, so we think there is a good chance this will work,” says von Caemmerer. “We expect to have a prototype within three years.”

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