Increasing Rubisco to future-proof C4 crops

What is it about?

All plants convert atmospheric CO2 into carbohydrates via the enzyme Rubisco, which plays a key role in photosynthesis. In this study, we increased Rubisco abundance and activity in sorghum and sugarcane leaves by upregulating two genes, the Rubisco small subunit (RbcS) and Rubisco accumulation factor 1 (Raf1). We show that by adding more of this enzyme, sorghum and sugarcane plants were able to take up more CO2, resulting in increased photosynthesis and productivity, including in a field trial of sorghum. We also found that the transgenic sorghum plants were able to induce photosynthesis faster upon shade-to-sun transitions, which frequently occur under the fluctuating light conditions of crop canopies in the field. Our results suggest a potential opportunity to achieve substantial productivity increases in C4 crops, a group of biologically similar crops that accounts for a large proportion of global agricultural output and includes sorghum, sugarcane, and maize.

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Why is it important?

As global climate change proceeds, understanding how to future-proof crops is more crucial than ever. Our findings suggest that Rubisco may have become a limitation to C4 crops only within the last few decades, due to rising atmospheric CO2 concentrations. Identifying this short time frame helps explain why natural selection and breeding have not increased Rubisco abundance in these economically important crops despite the apparent benefits, and highlights the key role biotechnology can play in ensuring future food security. This work also provides the first proof-of-concept that upregulating Rubisco is possible across the broad group of C4 crops, and that it results in increased productivity in the field and greenhouse. Testing Rubisco upregulation in elite cultivars and in multi-location multi-year field trials is the next proving step for achieving sustainable yield increases under rising atmospheric CO2 through this new approach.