Expression of barley SUSIBA2 transcription factor yields high-starch low-methane rice

Abstract

Atmospheric methane is the second most important greenhouse gas after carbon dioxide, and is responsible for about 20% of the global warming effect since pre-industrial times. Rice paddies are the largest anthropogenic methane source and produce 7-17% of atmospheric methane. Warm waterlogged soil and exuded nutrients from rice roots provide ideal conditions for methanogenesis in paddies with annual methane emissions of 25-100-million tonnes. This scenario will be exacerbated by an expansion in rice cultivation needed to meet the escalating demand for food in the coming decades. There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies. However, ongoing efforts for methane mitigation in rice paddies are mainly based on farming practices and measures that are difficult to implement. Despite proposed strategies to increase rice productivity and reduce methane emissions, no high-starch low-methane-emission rice has been developed. Here we show that the addition of a single transcription factor gene, barley SUSIBA2 (refs 7, 8), conferred a shift of carbon flux to SUSIBA2 rice, favouring the allocation of photosynthates to aboveground biomass over allocation to roots. The altered allocation resulted in an increased biomass and starch content in the seeds and stems, and suppressed methanogenesis, possibly through a reduction in root exudates. Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels. SUSIBA2 rice offers a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation. Approaches to increase rice productivity and reduce methane emissions as seen in SUSIBA2 rice may be particularly beneficial in a future climate with rising temperatures resulting in increased methane emissions from paddies.

Rhizosphere engineering: Enhancing sustainable plant ecosystem productivity

“…Understanding how to control photosynthate distribution in plants are key to being able to alter its allocation between aboveground and belowground biomass, as was demonstrated (e.g., in the "low-methane high-starch" rice project) (Su et al 2015) and in work on carbohydrate transporters (Ryan et al 2009). An alternative option is to explore genotypic diversity in selecting crops or native-ecosystem plants with desirable traits for carbon allocation and partitioning.…”

Effect of rice cultivars on yield-scaled methane emissions in a double rice field in South China

“…However, one recent study identified no significant relationship between methane emissions and any plant growth parameters, even though rice grain yield and other plant growth characteristics were significantly different among the different cultivars ). This may be because some cultivars appear to allocate more of the products of photosynthesis to root exudation than others (Su et al 2015).…”

“…The emission of methane to the atmosphere consists of three pathways: molecular diffusion, ebullition and plant-mediated transport (Wassmann et al 1996;Khosa et al 2010). Among the climatic, environmental and field management factors influencing methane emissions from rice paddy, rice cultivar is one of the most influential factors (Mosier et al 1990;Chen et al 1997;Fu et al 2009;Baruah et al 2010;Su et al 2015). Of the total methane emitted from a rice field during the growing season, 60-90% is transported through the rice plants rather than through molecular diffusion across water-air interfaces or through the release of gas bubbles (Holzapfel-Pschorn et al 1986;Schütz et al 1989;.…”

Metagenomics analysis of methane metabolisms in manure fertilized paddy soil

“…Lamendella et al (2011) reported that carbohydrate metabolism functional genes were highly abundant in pig feces (>13%), therefore there may be a chance that the use of pig manure may have introduced microbes owning genes related to carbohydrate metabolisms to paddy soils. Recently, genetically modified rice was developed in order to increase aboveground biomass, which consequently reduced root exudates (Su et al, 2015). According to the study, the alteration suppressed the carbohydrate availability in rhizosphere, which consequently reduced significant amount of methane emission from rice.…”