PLANTS are badly out of date. They gained their photosynthetic machinery in one fell swoop a billion years ago, by enslaving bacteria that had the ability to convert sunlight into chemical energy. Plants went on to conquer the land and green the earth, but they also became victims of their own early success. Their enslaved cyanobacteria have had little scope to evolve, meaning plants can struggle to cope as the atmosphere changes.
The free-living relatives of those bacteria, however, have been able to evolve unfettered. Their photosynthetic machinery is faster and more efficient, allowing them to capture more of the sun’s energy.
Scientists have long dreamed of upgrading crop plants with the better photosynthetic machinery of free-living cyanobacteria. Until recently all attempts had failed, but now they’ve taken a huge step forward.
A joint team from Cornell University in New York and Rothamsted Research in the UK has successfully replaced a key enzyme in tobacco plants with a faster version from a cyanobacterium (Nature, vol 513, p 547). Their success promises huge gains in agricultural productivity – but is likely to become controversial as people wake up to the implications.
The enzyme in question is called RuBisCo, which catalyses the reaction that “fixes” carbon dioxide from the air to make into sugars. It is the most important enzyme in the world – almost all living things rely on it for food. But it is incredibly slow, catalysing only about three reactions per second. A typical enzyme gets through tens of thousands. It is also wasteful. RuBisCo evolved at a time when the atmosphere was rich in CO2 but devoid of oxygen. Now there’s lots of oxygen and relatively little CO2, and RuBisCo has a habit of mistaking oxygen for CO2, which wastes large amounts of energy.
Its inefficiency is the main factor limiting how much of the sun’s energy plants can capture. The version found in most plants has become better at identifying CO2, but at the cost of making it even slower. Meanwhile, free cyanobacteria found a way to concentrate CO2 around RuBisCo, so that they could keep the faster version.
Hence the desire to upgrade crop plants by adding cyanobacterial machinery, which could boost yields by about 25 per cent (New Scientist, 22 February 2011, p 42). What’s more, such plants will need less water, because they don’t need to keep their pores open as much, meaning they can better retain moisture.
That is what the Cornell and Rothamsted collaboration is working towards. They are not there quite yet: a few more parts of the cyanobacterial system need to be transferred for their plants to take full advantage. But the work is a massive step forward.
It now seems certain that supercrops with “turbocharged photosynthesis” will be growing in our fields in a few decades, if not sooner. This seems like great news in a world where demand for food, biofuels and plant materials like cotton continues to increase, and where global warming will have an ever greater impact on crop production. More productive plants means greater yields.
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But there is a danger too. Critics of genetic modification have long argued that GM crops will spread in the wild, or that their modified genes will “pollute” wild relatives, with disastrous effects. So far these fears seem exaggerated. There are monster plants running rampant through many countries, but they are not GM creations – they are invasive species.
This is not surprising: most GM traits are not useful to wild plants. A trait such as herbicide resistance is only useful to plants growing in areas where herbicides are used, such as in fields and road verges.
Upgrading photosynthesis is a different story. If biologists succeed in boosting it by 25 per cent or more, the upgraded plants are going to have a big advantage over their unmodified cousins. And that could spell trouble.
There is a precedent. About 30 million years ago some plants evolved a way to concentrate CO2 like cyanobacteria do. These are called C4 plants, and although they make up only 4 per cent of plant species, they account for 25 per cent of plant biomass. Look out over a grassy savannah and just about every living thing you see will be a C4 plant.
If we fill our fields with supercrops and plant forests of supertrees it seems inevitable that they will turn feral and, like C4 plants before them, come to dominate some ecosystems – though it might take millennia. That prospect will horrify many. When anti-GM campaigners start protesting against the introduction of turbocharged crops, they will have a point: the wisdom of growing superplants in open fields is definitely debatable.
But the arguments in favour – boosting agricultural yield to feed more people with less land while also sucking more CO2 out of the atmosphere – are also powerful. And there’s another side to it. Wild animals need to eat too, and we’re not leaving much for them. An ecosystem based on superplants would support more life overall.
If society decided to go ahead, another choice would almost certainly come up. We could just stand by and let boosted grains, vegetables and trees run wild, possibly driving some other plant species to extinction. Or we could level the playing field by upgrading many wild plants too.
This may seem like a shocking idea. But the reality is that we are way, way past the point where we can preserve Earth the way it was before we came to the fore.
We are already well into the Anthropocene. The areas we think of as wild and untouched are nothing like they were before our ancestors arrived. The apples and bananas we feast on are much-mutated monsters compared with their wild relatives.
If we are going to reshape plants so that they can make more food, why not do it in a way that benefits most life on Earth, not just us humans?