Effects Of Rice G Protein A Subunit Mutant On Root Morphological And Physiological Traits And Methane Emission From Paddy Fields And Their Mechanisms

The methane emission from paddy field plays an important role in the global methane emission,and rice plants play an important role in methane emission from paddy fields.G protein a subunit(G?)is involved in the regulation of many important biological processes in rice.The study on the regulation of Ga on rice root morphological and physiological traits and its effect on methane emission from paddy fields can provide theoretical and practical values in methane mitigation.In the present study,rice root morphological and physiological traits,root and leaf sheath aerenchyma,the abundance of methanogenic and methanotroph in soil,activity of methanotroph,and their relationships with methane production,oxygen and transportation were investigated using with the wild type 9311 and Ga knockdown mutant rga1 as materials.The role of Ga in the formation of root aerechyma mediated by hydrogen peroxide was also studied.The main results were as follows:(1)The methane emissions from mutant rgal paddy field were higher than that from 9311.The methane emission from the middle stage of rice growth(40-82 d)was 40.3-49.2%of the cumulative CH4 during the whole growth period.The methane emission fluxes of rgal were 36.8-56.3%higher than those of 9311 and the cumulative methane emission of rgal was 53.3%higher than that of 9311 during the middle stage of rice growth.There was no significant difference in methane emission at vegetative growth stage(1-40 d)and reproductive growth stage(82-110 d).Therefore,the difference in the morphological and physiological characteristics of rgal and 9311 in the middle stage of rice growth,as well as the effect on methanogenic and methanotroph in rhizosphere was the main reason for higher methane emission in rgal paddy.(2)The root dry weight,length,number,surface area,oxidation activity and radial oxygen loss of rgal were significantly lower than those of 9311.The root diameter was not significantly different from that of 9311.The root shoot ratio was significantly higher than that of 9311.The root oxidation activity and radial oxygen loss were smaller than those of 9311.The results indicated that compared to 9311,rgal root system was small and conducive to the transportation of oxygen to the rhizosphere soil,inhibited the growth of methanogenic and reduces the methanotroph,thus increased the methane emission in the paddy field.(3)Aerenchyma of mutant rgal affects methane emission in paddy fields.The methane released greater with more area of the leaf sheath aerenchyma.There was significant positive correlation between methane emission and leaf sheath aerenchyma area(r?0.900*-0.980*).The methane released greater with less area of the root aerenchyma.There was significant negative correlation between methane emission and root aerenchyma area(r =-0.833*).The leaf sheath aerenchyma of 9311 were significantly smaller than rgal,and the transmission ability of aerenchyma of leaf sheath to methane was reduced.The root aerenchyma of 9311 was more developed than rgal,which improved the transmission ability of rice root to oxygen,was beneficial to the growth of methanotroph in the rhizosphere soil,promoted the oxidation of methane and reduced the methane emission.(4)G protein was involved in the process of cell death and aerenchyma formation in rice root cortical cells mediated by hydrogen peroxide.The content of H2O2 at the root tip 1 cm of mutant rgal was higher than that of wild type 9311,and the cell death rate was less than that of wild type 9311.The absence of caused abnormal cell death mediated by hydrogen peroxide,which affected the formation of root aerenchyma.The accumulation of H2O2 in rgal was accompanied by upregulation of Rboh,which produce H2O2,and downregulation of MT2b,which encodes a reactive oxygen scavenger.Downregulation the level of XET gene expression induced high cell death in root cortex.Thus,G protein was involved in the process of cell death and aerenchyma formation in rice root cortical cells mediated by hydrogen peroxide.(5)Mutant rgal changed the abundance of methanogenic and methanotroph in rhizosphere soil.The mutant rgal increased the percentage of dominant species of methanogenic in rhizosphere soil and reduced the percentage of the dominant species of methanotroph.The Methanobacteriulm,Methanoregula,Methanosphaera are the dominant species of methanogenic in rhizosphere soil.The percentage of dominant species of methanogenic inrhizosphere soil of rgal is higher than that in 9311.The Methylomonas,Methylovulum,Methylosarcina in methanotroph is the dominant species of methanotroph.The percentage of dominant species of methanotroph inrhizosphere soil of rgal is lower than that in 9311.(6)Mutant rgal inhibits the activity of methanotroph in rhizosphere soil and inhibits methane oxidation.The mutant rgal lacks the G protein a subunit,which results in the inhibition of the formation of the root aerenchyma.It leads to a decrease in the ability of the root to transfer oxygen to the rhizosphere soil,inhibit the growth and activity of methanotroph and increase methane emission from paddy fields.In summary,mutant rga1,lacking G protein ? subunit,promoted the formation of leaf sheath aerenchyma and inhibited the formation of root aerenchyma.The development of leaf sheath aerenchyma is beneficial to the transport of methane and increase the methane emissionin paddy fields.Underdeveloped root aerenchyma reduces root oxidation activity and radial oxygen loss,reduces the transmission of oxygen to the rhizosphere soil.It affected the percentage and abundance of methanogenic and methanotroph in soil,inhibited the growth and activity of methanotroph,reduced the oxidation of methane,and ultimately lead to an increase in the methane emissions from the paddy fields of rgal.