Effects Of OsRGA1 On Photosynthate Allocation In Rice Root And Methane Emissions In Paddy Fields

Methane(CH4)is a significant greenhouse gas and rice(Oryza sativa L.)paddies are considered an important source of global CH4 emissions.Rice roots absorb nutrients and water from the soil and release photosynthate to the rhizosphere in the form of root exudates.Root exudates provide carbon source and energy for methane production and regulate rhizosphere microbial community structure and abundance.OsRGA1 which encoding rice G-protein α-subunit regulates rice photosynthesis and root formation.However,the interactive effects of rice roots and soils on CH4 emissions in paddy fields and the regulation of OsRGAl in this process are not clearly understood.In this study,two different rice cultivars,wild-type Yangdao 6(YD 6)and OsRGA1 null mutant rga1,were selected as experimental materials.Field experiments,meta-analysis and RNA-seq analysis were used in this study.Two nitrogen fertilizer application(0N,0 kg N ha-1;NN,270 kg N ha-1)and leaf-cutting trial during booting stage were conducted.In order to clarify the main traits driving methane emission in rice paddies and the coordination mechanism of OsRGAl in reducing methane emission and improving yield,we investigated the effect of nitrogen application and root biomass on methane emissions,determined methane emissions,plant morphology and physiology,root exudates,and rhizosphere microorganisms.Main results are as follows:1.Meta-analysis based on data of the past 30 years suggested that methane fluxes decreased with increasing root biomass between cultivars during the latest decade,with an effect size of-15.69%.N rates showed positive effects of 8.44%on methane emissions,and N rates of 250-300 kg ha-1 stimulated CH4 emissions by the highest amount of 26.95%.2.Three-year field experiment showed that total CH4 emission at the whole growth stage and average CH4 flux at the booting stage(BT)of rga1 were 22%and 34%higher than that of YD 6 under NN condition,respectively.The difference of total CH4 emission for two rice cultivars was due to different CH4 flux at BT.There were significantly reduced both total CH4 emissions but no significant difference in CH4 emission between the two cultivars under 0N condition.The yield of YD 6 was 89.44%and 90.34%higher than that of rgal under NN and 0N conditions,respectively.Therefore,OsRGA1 can depress CH4 emissions at two scales(actual emissions and production scales),thus reducing the global warming potential and greenhouse gas emission intensity.3.Compared with rgal,the YD 6 exhibited lower plant height and total organic carbon(TOC)in root exudates,and higher plant height,biomass accumulation,root oxidation activity(ROA),root nonstructural carbohydrate(NSC)and the ratio of NSC to TOC(NSC/TOC)under NN condition.The PCA and Mantel analysis on related traits confirmed that NSC/TOC was the main driving factor of CH4 emissions in paddy fields.4.RNA-seq analysis showed that genes encoding enzymes of transportation/uploading,glycolysis/gluconeogenesis and citric acid cycle were downregulated and those involving in polysaccharide synthesis were upregulated in YD 6 compared with rgal under NN condition.Combined with the analysis of root exudate components,OsRGA1 can coordinate the photosynthate allocation of root assimilation and rhizodeposition.Therefore,OsRGA1 null mutation inhibited the establishment of roots,but increased root exudates,which is conducive to the survival of methanogens and resulting in high methane emissions.5.Exogenous matters incubation experiment confirmed the inhibitory effect of nitrogen on methanotrophs,while organic acids increased the activity of methanotrophs.OsPTR9,OsNRT,and OsPTR5 that are genes related to nitrogen uptake and transport were upregulated,leading to significantly higher nitrogen-use efficiency than rga1 in YD 6.Therefore,more photosynthates were allocated in root anabolism process,leading to the increase of major organic acids in the rhizosphere and alleviating the inhibiting effects of nitrogen on methanotrophs,thus promoting the oxidation of methane in the rhizosphere,and achieved low methane emissions from paddy fields.This study investigated the mechanism of photosynthate allocation in rice root driven CH4 emissions and confirmed the mechanism of OsRGAl in the interaction of rice roots and soil to regulate CH4 emissions in paddy fields,which could provide theoretical and practical basis for methane emission reduction in paddy fields.