How to make corn more like cactus

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EXCERPTS: Scientists are trying to teach old crops some new tricks that will let them flourish in these harsher conditions — turning to secrets that reside in plants like pineapples, orchids and agaves. These and certain other plants have hacked photosynthesis in ways that allow them to thrive when it’s hot and dry, and even to withstand blistering periods of drought.

Many orchids, for example, live in nooks and crannies of trees where their only water comes in sporadic bouts of rain, while others, like agaves, thrive in the rocky soils of desert grasslands. If scientists could engineer crop plants like rice and wheat to be more like these heat-tolerant species, crops could be grown in lands that can’t be farmed right now. Under the right conditions, researchers say, some crop yields could increase by 50 percent or more.

The work is still years from being done, but it could be vital. Climate change is predicted to cause more droughts and make farmland less productive. At the same time, the number of people the world needs to feed will increase to 10 billion from 8 billion by the end of the century.

[...] This version of photosynthesis is how 85 percent of all plants do things, including most trees and most major food crops — rice, wheat, soybeans and more. Such plants are referred to as C3 plants because they make a three-carbon molecule in one of the first steps of photosynthesis.

[...] Plants have figured out two slightly different ways to get around the problem and scientists are hoping to exploit both of them. Some plants use a process called Crassulacean acid metabolism, or CAM: They take in CO 2 during the night, while it’s relatively cool, and concentrate and store it until it can be used during the day to make sugars. Other plants — known as C4 plants — concentrate and store carbon dioxide in specialized cells, thus avoiding the wasteful photorespiration.

In both cases, these plants have separated the part of photosynthesis that captures carbon dioxide from the air from the part of the process where rubisco grabs the CO2 and begins the process of turning it into a sugar. CAM plants separate the processes according to time of day, and C4 plants separate them physically in different parts of the plant.

The adaptations help plants in two different ways. In the first place, they save water, letting the plant make do with less. Just as important, by limiting the wasteful effects of photorespiration they let the plants grow bigger from the same amount of nutrients.

[...] Many scientists think CAM is a promising target for engineering. Because CAM evolved independently many times in many different plants, there shouldn’t be a fundamental barrier to inducing the process in non-CAM plants, Katharina Schiller and Andrea Bräutigam write in the 2021 Annual Review of Plant Biology.

In fact, CAM seems to rely on enzymes and other molecular machinery that are already found in C3 plants — they just use them in different ways at different times. That suggests it’s possible to repurpose already existing genes in normal plants to make them CAM plants. But that is easier said than done...

[...] Another approach to keeping photosynthesis humming along efficiently even when it’s hot and dry is to engineer C4 traits into C3 plants. Many of our cereal crops are already C4 plants, including corn, sugarcane and sorghum, and evidence suggests that the trait has evolved independently upwards of 60 times. (C4 is named after a characteristic four-carbon molecule produced by the plants during photosynthesis, compared with the three-carbon molecule produced by C3 plants.)

[...] Although the C4 and CAM approaches share similarities, they have different strengths and weaknesses... (MORE - missing details)

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