Chaperones: a key to achieving enhanced crop yields

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Maxim Kapralov (L) and Spencer Whitney. Image: Charles Tambiah /ARC CoETP

Every time you have a piece of toast, breathe or sit under the shade of a tree you are enjoying the products of photosynthesis, a process that makes possible the conversion of sunlight and carbon dioxide (CO2) into sugars. One enzyme in this process, called Rubisco, is the most abundant protein on the planet. It also has one of the most significant responsibilities to life on Earth: the conversion of CO2 to organic compounds like the ones found in your cells, your bread and plant leaves.

Rubisco has baffled scientists for over 50 years as it is surprisingly inefficient at its job. Every second, Rubisco is only able to fix one or two CO2 molecules while at the same time, other plant enzymes complete tens to thousands of cycles. Adding to this sluggish behaviour, the Rubisco enzyme has a highly complex structure and assembling its sixteen pieces requires the assistance of more than twelve other proteins called chaperones.

A team of scientists from the ARC Centre of Excellence for Translational Photosynthesis at The Australian National University in collaboration with the University of Wollongong, have just published a study about the importance of the particularly close relationship between Rubisco and its “RAF1” chaperone.

The study, published in the latest PNAS journal, shows that Rubisco and RAF1 have evolved together, so changes in one protein requires a balancing change in the other. Understanding this partnership has important implications with regard to ongoing efforts to accelerate Rubisco activity – a key goal for improving crop productivity.

“We have been able to elevate the production of a modified Rubisco in leaves by inserting a modified complimentary version of RAF1”, says Spencer Whitney, leader of the research team.

“Including RAF1 caused Rubisco’s levels to double, and as a result, we obtained faster rates of photosynthesis and plant growth compared to the plants where RAF1 was not introduced,” says Dr Whitney.

“The finding also explains why our prior attempts to insert more efficient versions of Rubisco from some algae into plant leaves have failed – they require different chaperones to those available in leaf cells,” says Dr Whitney.

Rubisco structure

Rubisco and RAF1

This result represents a milestone towards increasing the photosynthetic rate in crop plants that invest heavily in Rubisco, in which only five percent of the sunlight is converted into sugars”, he says.

In a world with increasing demands for food, this discovery represents an important advance in efforts to increase the yields of some of our most important staple crops, such as wheat, cotton and rice.

This study was funded by the Australian Research Council (ARC) and the Realizing Increased Photosynthetic Efficiency (RIPE) project.

See ANU Media Release “Spurring production of a sluggish enzyme for crop yields”