Investigation On The Effects Of Expression Regulation Of Key Genes Involved In Starch Metabolism And Sugar Transport In Rice

The photosynthate is mainly metabolized and transported in the form of starch and soluble sugar in rice source-sink system.The metabolic rate of starch and the transport efficiency of soluble sugar determine the relationship among rice source,sink and reservoir flow,which in turn affects rice yield and quality.From the fixation of CO2 in rice leaves to the storage of starch in endosperm,the enzymes encoded by OsGWD1,OsMEX1,OspGlcT,OsAGPS2 and OsAGPL2 play important roles in the processes of the metabolism and transport of starch and soluble sugar.Based on previous results of gene functions of each gene in model plant,we generated the overexpression and CRISPR/Cas9 knockout transgenic rice of each gene,and further screened their representative transgenic rice for following functional study.By using these transgenic rice,plant growth and development,rice yield and quality,and other agronomic traits were analyzed,thus facilitating the evaluation of the effects of their expression on rice morphogenesis,yield and quality.Therefore,the present study provides rich gene resources and genetic materials for further breeding programs of elite rice with high-yield and quality.The major research results are as following:1、We created three different kinds of transgenic rice that overexpressed OsGWD1,OsMEX1 and OspGlcT,as well as OsAGPS2 and OsAGPL2,respectively.Expression analysis indicated that all the constructs were successfully introduced and expressed in the recipient rice.In addition,we also successfully created knock-out mutants of each gene,including OsGWD1,OsMEX1,OspGlcT,OsAGPS2 and OsAGPL2,by using CRISPR/Cas9 gene editing technology.2The OsGWD1 overexpression rice exhibited elevated plant height,longer and wider rice,and increased 1000-grain weight.Moreover,the thermodynamic properties of rice also changed,including:increased gelatinization temperature and thermal enthalpy value.In addition,overexpression of OsGWD1 gene could improve the drought tolerance of seeds during germination.Knock-out of OsGWD1 reduced rice tiller number,and the change of grain size was consistent with that in the overexpression lines.The other agronomic traits,including 1000-grain weight and rice quality,had no significant changes.3、Overexpression of OsMEX1 and OspGlcT simultaneously reduced rice tiller number,increased plant height and 1000-grain weight,and made rice seed longer and wider.In addition,the initial gelatinization temperature To,peak gelatinization temperature Tp,termination gelatinization temperature Tc and theraial enthalpy value AH of the transgenic rice were all significantly increased.In response to ABA stress,the chlorophyll content of the wild-type control was reduced while that of the overexpression lines was increased.Under low temperature stress,the transgenic lines showed certain increased cold tolerance.Rice mutant with either OsMEX1 or OspGlcT knocked-out exhibited reduced tiller number,plant height and 1000-grain weight.Also the seed size became longer and narrower,but the rice quality had no significant change.4、Co-overexpression of OsAGPS2 and OsAGPL2 slightly reduced the apparent amylose content of the transgenic rice.Moreover,the grain chalk and gel consistency also had certain changes.Knock-out of OsAGPS2 inhibited grain filling process and caused severe empty grain rate,which affected rice yield and seed fertility seriously.In addition,knock-out of OsAGPL2 decreased the 1000-grain weight and increased its apparent amylose content.