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科学家改进植物光合作用,使植物光合效率提高40%

科学家改进植物光合作用,使植物光合效率提高40%
Credit: James Baltz/College of Agricultural, Consumer and Environmental Sciences

众所周知,植物都是通过光合作用来获取能量的,但是地球上大部分的植物在光合作用时都出了偏差,使得他们不得不在漫长的进化中额外进化出了一个名为“光呼吸”的步骤来修正这一偏差,但是这也导致大量的能量浪费,光合作用的整体效率相对较低。而最近灯塔国伊利诺伊大学的研究人员在《科学》上发表的一篇论文表示他们改进了植物的这一问题的一部分,应用到现实农业中的话可以使植物的光合作用效率提高40%以上。

如果简单的用全球农作物产量来换算一下的话,之前植物损失掉的光合作用的能量可以轻松养活2亿人口。以下是对植物光合作用缺陷的简单描述:

大部分植物在进行光合作用的时候,都要经过一个关键步骤,即核酮糖-1,5-二磷酸羧化酶加氧酶(简称RuBisCO)将二氧化碳楔入到化合物核酮糖-1,5-二磷酸(简称RuBP)中。在每天大约20%的时间里,RuBisCO会错误地将氧分子当成二氧化碳分子楔入到RuBP中,这个过程不仅浪费了氧气和其他资源,还产生了乙醇酸盐和氨这两种有毒的化合物。而随着全球气温的升高,Rubisco从空气中提取二氧化碳的难度更大,从而导致更多的光呼吸产生

而植物通过光呼吸消耗一定的能量和营养物质解决了这一问题。而科学家们对这一链条中改进的部分正是光呼吸的部分,我们可以简单的把其认为是植物的自我解毒过程。科学家们通过设计新的替代路径来提高光呼吸过程的效率,使得植物能消耗更少的能量和营养物质就得以完成自我解毒的过程。

光呼吸通常在植物细胞中的三个小室进行复杂的作用,而为了减少光呼吸的产生,要么减少上一步中Rubisco错误嵌入氧分子的产生;要么制造一种生物酶能够直接替代光呼吸作用的效果。而研究小组正是通过基因剪辑技术,使用了植物苹果酸合成酶基因和一个绿藻基因来合成了一种乙醇酸脱氢酶,这种酶可以直接消耗掉错误合成的乙醇酸盐等物质。

两年多来,科学家们通过对1700多株不同基因结构植物的培养筛选,成功的发现了这一最具有效率的基因组合,具有这种基因组合的植物其生物体质量相比平均值高出了约40%。而研究小组现在正在测试这种基因组合对一些农作物的影响,包括大豆、豇豆、大米、土豆、番茄和茄子,以期成功提高其产量。

原文如下:

Plants convert sunlight into energy through photosynthesis; however, most crops on the planet are plagued by a photosynthetic glitch, and to deal with it, evolved an energy-expensive process called photorespiration that drastically suppresses their yield potential. Researchers from the University of Illinois and U.S. Department of Agriculture Agricultural Research Service report in the journal Science that crops engineered with a photorespiratory shortcut are 40 percent more productive in real-world agronomic conditions.

“We could feed up to 200 million additional people with the calories lost to photorespiration in the Midwestern U.S. each year,” said principal investigator Donald Ort, the Robert Emerson Professor of Plant Science and Crop Sciences at Illinois’ Carl R. Woese Institute for Genomic Biology. “Reclaiming even a portion of these calories across the world would go a long way to meeting the 21st Century’s rapidly expanding food demands—driven by population growth and more affluent high-calorie diets.”

This landmark study is part of Realizing Increased Photosynthetic Efficiency (RIPE), an international research project that is engineering crops to photosynthesize more efficiently to sustainably increase worldwide food productivity with support from the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research (FFAR), and the U.K. Government’s Department for International Development (DFID).

Photosynthesis uses the enzyme Rubisco—the planet’s most abundant protein—and sunlight energy to turn carbon dioxide and water into sugars that fuel plant growth and yield. Over millennia, Rubisco has become a victim of its own success, creating an oxygen-rich atmosphere. Unable to reliably distinguish between the two molecules, Rubisco grabs oxygen instead of carbon dioxide about 20 percent of the time, resulting in a plant-toxic compound that must be recycled through the process of photorespiration.

“Photorespiration is anti-photosynthesis,” said lead author Paul South, a research molecular biologist with the Agricultural Research Service, who works on the RIPE project at Illinois. “It costs the plant precious energy and resources that it could have invested in photosynthesis to produce more growth and yield.”

Photorespiration normally takes a complicated route through three compartments in the plant cell. Scientists engineered alternate pathways to reroute the process, drastically shortening the trip and saving enough resources to boost plant growth by 40 percent. This is the first time that an engineered photorespiration fix has been tested in real-world agronomic conditions.

“Much like the Panama Canal was a feat of engineering that increased the efficiency of trade, these photorespiratory shortcuts are a feat of plant engineering that prove a unique means to greatly increase the efficiency of photosynthesis,” said RIPE Director Stephen Long, the Ikenberry Endowed University Chair of Crop Sciences and Plant Biology at Illinois.

The team engineered three alternate routes to replace the circuitous native pathway. To optimize the new routes, they designed genetic constructs using different sets of promoters and genes, essentially creating a suite of unique roadmaps. They stress tested these roadmaps in 1,700 plants to winnow down the top performers.

Over two years of replicated field studies, they found that these engineered plants developed faster, grew taller, and produced about 40 percent more biomass, most of which was found in 50-percent-larger stems.

The team tested their hypotheses in tobacco: an ideal model plant for crop research because it is easier to modify and test than food crops, yet unlike alternative plant models, it develops a leaf canopy and can be tested in the field. Now, the team is translating these findings to boost the yield of soybean, cowpea, rice, potato, tomato, and eggplant.

“Rubisco has even more trouble picking out carbon dioxide from oxygen as it gets hotter, causing more photorespiration,” said co-author Amanda Cavanagh, an Illinois postdoctoral researcher working on the RIPE project. “Our goal is to build better plants that can take the heat today and in the future, to help equip farmers with the technology they need to feed the world.”

While it will likely take more than a decade for this technology to be translated into food crops and achieve regulatory approval, RIPE and its sponsors are committed to ensuring that smallholder farmers, particularly in Sub-Saharan Africa and Southeast Asia, will have royalty-free access to all of the project’s breakthroughs.

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