The Greening of Greenhouse Gas
✿ It’s a Gas: Driving through the Western Ghat mountains along the continental edge of the Deccan Plateau, I was charmed by this vista of sculpted terraces with verdant blades of rice emerging from submerged paddy fields. Little did I know then that paddy fields generate 50-100 million tonnes of methane each year, a potent greenhouse gas with 25 times the heat trapping potential of carbon dioxide. Although the flooded fields keep weeds at bay, microbes harbored under the warm, waterlogged soil feed on organic matter exuded by roots, releasing methane and accounting for about 20% of human-related production. In China, farmers have begun draining fields mid-season to interrupt methanogenic bacteria. But India is still responsible for nearly a third of the methane emissions.
✿ It’s Barley There: Now, thanks to genetic engineering, a new strain of rice yields more grain and produces less methane. Researchers spliced a gene from barley, encoding a master regulator (transcription factor) into rice. The gene, dubbed SUSIBA2 (acronym for “sugar signaling in barley 2”) increases the output of sugar and starch in the seeds, leaves and shoots of the rice plant, leaving less biomass in the root. This strongly decreased the methanogenic bacteria in the rhizosphere, or region around the root. In a 3-year field trial, methane emissions fell by 90%.
✿ Rice, Rice, Baby: The making of starch is under the direction of a set of genes which carry in front of them stretches of DNA sequences (promoters) known as sugar responsive elements or SURE. Aren’t you loving the acronyms? When a little bit of sugar is made, SUSIBA2 is activated and it turns on genes that make even more sugar, to create a snowballing effect. The sugar is converted to starch, diverting carbon to the grains and away from the root, starving the methane producing bacteria of food. Now that’s a sweet way to cool down our planet!
This work was a collaboration between scientists at Universities and non-profit research Institutes in Sweden, China and the US. The authors have no competing financial interests.
Paper (paywalled): http://www.nature.com/nature/journal/v523/n7562/full/nature14673.html