Photosynthesis is the foundation of virtually all life on Earth. Using energy from sunlight, plants accomplish the astonishing feat of converting water from the soil and carbon dioxide (CO2) from the air into everything from tiny mosses that carpet moist rocks and logs, to sweeping grasslands, to towering redwoods. All of the carbon transformed in this way to create the natural world around us was first fixed from the atmosphere and converted into living matter through the enzyme Rubisco, which may be the most abundant protein on the planet.^1–3 As photosynthesis is the means by which virtually all carbon enters the biosphere, every atom of carbon in our own bodies is there because, at some point, it was plucked from the air by Rubisco. An impressive accomplishment for a single enzyme!

Yet Rubisco has a fundamental weakness, which billions of years of evolution have not solved – when atmospheric CO2 is low relative to molecular oxygen (O2), Rubisco fails to distinguish between the two and is prone to mistakenly fixing O2. The product of O2 fixation is of little use to plants, which must invoke a costly metabolic process known as photorespiration to prevent it from accumulating to toxic levels.⁴ Photorespiration consumes energy and results in the loss of previously fixed CO2. In the relatively low CO2, high O2 atmosphere that has existed on Earth for the last 30 million years, photorespiration can significantly reduce photosynthetic efficiency.^5,6 There is thus high selective pressure for evolutionary innovations that solve or circumvent this flaw in Rubisco.