Effects Of DEP1 Deletion Mutant On Rice Root Aerenchyma And Methane Emissions From Paddy Fields And Their Mechanisms

Methane is an important greenhouse gas with a contribution rate of 15-20%to the greenhouse effect,preceded only to carbon dioxide.Paddy field is one of the main sources of atmospheric methane,and the growth characteristics of rice roots are closely related to methane emission from paddy fields.The G protein y subunit DEP1 affects the aboveground morphological characteristics of rice such as panicle type and grain size,and regulates growth and development in rice by adjusting the nitrogen utilization rate,but the effects of DEP1 on rice root are not clear yet.Therefore,we can analyse the correlation between the regulation of rice root morphological and physiological characteristics by DEP1 and the methane emission from paddy fields to provide a certain degree of theoretical basis for greenhouse gas emission reduction.In this study,DEP1 deletion mutant Wuyunjing 8(W8)and its stable transgenic complementary line W8(DEP1)were used as materials to research the effects of DEP1 on the related characteristics of rice root system,including morphological and physiological characteristics and aerenchyma,as well as the soil microbial abundance to figure out the mechanism of DEP1’s influence on methane emission from paddy fields.The main results were as follows:(1)DEP1 was involved in hydrogen peroxide-mediated parenchyma cell death and aerenchyma formation in rice root.Compared with W8(DEP1),the aerenchyma area and proportion,death rate of parenchyma cells and H2O2 content of W8 root were reduced.The accumulation of H2O2 at the initial position of cell death and content of H2O2 in roots of W8(DEP1)were higher,and the enzymatic mechanism of scavenging H2O2 in roots of W8(DEP1)was more active.Exogenous treatment results showed that DEP1 promoted the production of hydrogen peroxide in roots of W8(DEP1)by increasing the expression of Rboh,and the expression of XET went up to promote cell death.Therefore,the deletion of DEP1 reduced the expression of Rboh,which can produce H2O2,to inhibit the accumulation of hydrogen peroxide in W8 roots.At the same time,the expression of XET gene that promoted cell death was suppressed to debase cell death rate,finally the area and proportion of aerenchyma in W8 roots were reduced.(2)DEP1 deletion affected the morphological and physiological characteristics of rice roots and methane emission from paddy fields.The root physiological characteristics that included root dry weight,length,surface area,number,the ratio of aerenchyma,root absorption surface area,root active absorption surface area.root oxidation activity and radial oxygen loss were significantly lower than those of W8(DEP1).The root diameter of W8 was not significantly different from that of W8(DEP1).and the root/shoot ratio of W8 was significantly higher than W8(DEP1).Furthermore,the root ROL barrier of W8 was stronger than W8(DEP1).The total methane emission during the whole growth period and the methane emission flux of different periods from W8 paddy fields were both higher than W8(DEP1).The difference of methane emission from paddy fields between W8 and W8(DEP1)was particularly significant in the middle growth stage(40-80 d,booting stage),and the methane emission of W8 at booting stage was 37.15%higher than that of W8(DEP1).Correlation analysis showed that methane emission from paddy fields at booting stage was negatively correlated with rice root length,surface area,number,aerenchyma area,absorption surface area,active absorption area,root oxidation activity and radial oxygen loss(r=-0.947**～-0.839*).The deletion of DEP1 caused that the root system of W8 was less developed,the ROL barrier of the root outer cortex was also thickened,and the proportion of aerenchyma area was debased,as well as the root oxidation activity and radial oxygen loss were lower,which resulted that the transportation of oxygen from the aerobic part to the root tips was suppressed and reduced methane oxidation,ultimately the methane emission from W8 rice fields was higher than W8(DEP1)(3)DEP1 deletion decreased the number of methanotrophs in the rhizosphere soil.During booting stage.W8(DEP1)had significantly higher methanotrophs in the rhizosphere soil than W8,and the ratio of methanogens/methanotrophs of W8(DEP1)was significantly lower than W8.There was no significant difference in the number of methanogens between W8(DEP1)and W8.It showed that the deletion of DEP1 in W8 had no effect on the methane production process,but it reduced the abundance of methanotrophs in the rhizosphere soil and suppressed methane oxidation activity,thus increased methane emission from paddy field In summary，DEP1 promoted the production of hydrogen peroxide and induced the death of parenchyma cell by regulating the hydrogen peroxide-mediated cell death pathway to accelerate the formation of root aerenchyma area,and enhanced the development of rice roots at the same time,also inhibited the formation of ROL barriers in roots.The effects of DEP1 on the morphological traits of rice root improved the oxidation activity and radial oxygen loss of the root system to enhance the oxygen transportation to the rhizosphere of rice,and increased the oxygen content in the rhizosphere soil to promote the growth of methanotrophs,then promoted oxidation of methane at the rhizosphere to reduce methane emission from paddy field.