美国科学家研发出增产40%的转基因作物
美国《科学》杂志日前刊发一项研究成果说，美国研究人员利用基因工程手段缩短农作物的“光呼吸”路径，可使某些农作物增产达40%，有望用于应对全球人口增长带来的粮食短缺挑战。
植物通过光合作用将二氧化碳和水转化为能量，“二磷酸核酮糖羧化酶”是参与光合作用的关键酶。在富氧环境中，这种酶会错把氧气分子认作二氧化碳，与之结合生成有害物质。这种光合作用“小故障”导致的有毒中间产物要依靠“光呼吸”降解，但后者是一个损耗能量的过程，不利于提高产量。
为节省这种能量的消耗，伊利诺伊大学厄巴纳-尚佩恩分校等机构研究人员通过一系列的基因改造和调控设计出3种不同的“光呼吸”替代路径，大大缩短了“光呼吸”原本迂回复杂的反应路径。随后，他们在实验室中对约1700种植物进行压力测试，筛选出表现最优的基因，不断优化“光呼吸”替代反应的路线。
在为期两年的田野研究中，他们发现，经基因改造缩短“光呼吸”路径的作物生长更快、更高、茎部更粗大，比普通作物多产出40%的生物质能。目前，田野研究主要利用烟草展开，下一步研究人员将尝试用这种技术使大豆、豇豆、大米、马铃薯、西红柿、茄子等农作物增产。
“这种‘光呼吸’捷径是一项植物工程壮举，（实验）证明了它是一种能大幅提高光合作用效率的独特手段。”伊利诺伊大学厄巴纳-尚佩恩分校教授斯蒂芬·朗说。
Scientists Patch Photosynthesis Glitch to Make Plants Grow 40 Percent Larger
All that oxygen you enjoy breathing doesn’t just appear magically in the atmosphere. Earth is livable because plants around the globe pump out oxygen as a byproduct of photosynthesis, and some of them become tasty food crops in addition. However, photosynthesis isn’t perfect despite many eons of evolutionary refinement. Scientists from the University of Illinois have worked to correct for a flaw in photosynthesis, and that could improve crop yields by as much as 40 percent.
At the heart of the new research is a process in plants called photorespiration, which is not so much part of photosynthesis as it is a consequence of it. Like many biological processes, photosynthesis doesn’t work correctly 100 percent of the time. In fact, one of the main reactions in photosynthesis is only about 75 percent effective. The change comes in the process that plants undertake because of that inefficiency.
In photosynthesis, plants take water and carbon dioxide and process it to create sugars (food) and oxygen. Plants don’t need the oxygen, so it gets expelled. Happily, we do need oxygen, and we exhale carbon dioxide.
The problem addressed in the new study is with an enzyme called ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). This protein complex attaches a carbon dioxide molecule to ribulose-1,5-bisphosphate (RuBP). Over the ages, Earth’s atmosphere has become more oxygenated, and that means RuBisCO has to cope with more oxygen molecules mixed in with carbon dioxide. About a quarter of the time, RuBisCO grabs an oxygen molecule by mistake, and that has consequences inside a plant.
Scientists Don Ort (right), Paul South (center) and Amanda Cavanagh (left) study how well their plants modified to bypass photorespiration perform beside non-modified plants in real-world conditions.
When RuBisCO screws up, plants are left with toxic byproducts like glycolate and ammonia. It takes energy to process these compounds (through photorespiration), which is added to the energy loss from photosynthesis inefficiency. The study authors note that rice, wheat, and soybeans all suffer from this glitch, and RuBisCO gets even less accurate as temperatures rise. That means food supplies could go down as global warming becomes more severe.
The fix is part of a program called Realizing Increased Photosynthetic Efficiency (RIPE), and it relies on the introduction of new genes that improve growth. Usually, photorespiration takes a circuitous and complex route through three different cellular organelles. It consumes ATP (the energy currency of cells) that should be going to making the plant larger and stronger. RIPE focuses on making photorespiration quicker and more energy efficient.
The team developed three alternate pathways using new genetic sequences. They optimized these pathways across 1,700 different plants to identify the best approaches. Over the course of two years, the researchers tested the sequences using modified tobacco plants. That’s a common plant in science because its genome is exceptionally well-understood.
Those plants produced about 40 percent more biomass than non-modified plants. That indicates the more efficient photorespiration pathways save the plant considerable energy that can instead go toward growth. The next step is to incorporate the genes into food crops like soybean, cowpea, rice, and tomatoes.
It may take several years to integrate the revised photorespiration genes into food crops, which are more complicated than tobacco. The resulting plants would then have to be approved for human consumption by regulators — that’s no easy feat by itself, and there’s frequent anti-scientific opposition to genetically modified crops. RISE is supported by non-profits all over the world, including the Bill & Melinda Gates Foundation. Any seeds developed under RISE will be available royalty-free.
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