Function Analysis Of Sucrose Transporters(Ossuts)in Sucrose Transport In Rice

Sucrose produced by photosynthesis is the basis of rice yield.Sucrose is mainly transported through phloem to regulate the growth and development of rice.Sucrose transporter is an important node which controls the network of transport and distribution of photoassimilatse and it mainly involves in the apoplastic transport of sucrose.There are five SUT coding genes have been identified in the rice genome.The role of OsSUT3/4/5 in sucrose transport is unclear.To study the function of sucrose transporter in rice is helpful to reveal the transport and distribution mechanism of photoassimilates in plants.Firstly,we studied the tissue localization and subcellular localization of OsSUT1/3/4/5 by constructed pOsSUTs:GUS materials and 35S-pCAMBIA1305-GFP vectors.Meanwhile,we used CRISPR/Cas9 technology to create mutants of ossutl/3/4/5.Physiological changes of sucrose loading of source and sucrose unloading of grain in mutant materials were analyzed to elucidate the function of OsSUTs in sucrose transport.The main finds are shown as follows:1.Subcellular localization and tissue localization of sucrose transporters(OsSUTs).35S-pCAMBIA1305-GFP vectors and pCAMBIA1300-GUS transgenic rice materials were used to study the subcellular localization and tissue localization of OsSUTs.The results of subcellular localization showed that the OsSUT1/3/4/5 were localized on the cytoplasmic membrane,indicating that they had the characteristics of transmembrane transport of sucrose.The results of tissue localization showed that OsSUT1/4/5 were expressed with varying degrees during various growth period of rice.OsSUT1/4/5 were expressed in germinating seed,vascular bundle of leaf,leaf sheath and root,glume of spikelet at flowering stage,caryopsis at filling stage.These findings suggest that OsSUT1/4/5 play an important role in the process of sucrose transport during seed germination,phloem loading in source,longdistance transport of sucrose and the unloading of sucrose during grain filling.OsSUT1/3/4 were also expressed in anthers,which indicates that OsSUT1/3/4 are related to the regulation of sucrose input during pollen development.2.Function analysis of sucrose transporters(OsSUTs)in phloem loading in rice.In this study,CRISPR/Cas9 techniques were used to construct ossuts deletion variant rice lines to study the function of sucrose transporters involved in sucrose phloem loading.The results showed that the expression of OsSUT4 significantly increased after the mutation of OsSUT1.The photoassimilates in source could complete the normal transport,which indicated that OsSUT4 replaced OsSUT1 to accomplish the sucrose phloem loading.The expression of OsSUT4 decreased after the mutation of OsSUT3,while the expression of the OsSUT 1/5 increased.The photoassimilate was able to perform normal phloem loading of source in ossut3 mutant plants,which indicated that OsSUT 1/5 could compensate for the effect of functional loss of OsSUT 3/4 on phloem loading in source.After the mutation of OsSUT4,sucrose and starch were accumulated in rice leaves,and the loading of photoassimilates was blocked.Then the accumulation of photoassimilates caused the decrease of net photosynthetic rate.As a result,the phenotype of ossut4 mutant plants assumed smaller and the plant height of ossut4 mutation decreased compared with wild type.These results suggest that OsSUT4 play an important role in the phloem loading process of sucrose.The expression of OsSUT1 significantly decreased after the mutation of OsSUT5 and the function of sucrose transporter was limited.The transport of the photoassimilates of the ossut5 mutant plants was blocked in the source,which led to the increase of sucrose and starch in the leaves.In conclusion,OsSUT 1/4 play major roles in the sucrose phloem loading of the source.3.Function analysis of sucrose transporters(OsSUTs)in grain sucrose unloading in rice.In this study,ossuts deletion variant rice lines were used to study the function of sucrose transporters involved in grain phloem unloading.The results showed that rice grain filling was inhibited after the mutation of OsSUT1/5.The yield of ossutl/5 mutants showed a downward trend.The results indicats that OsSUT1 and OsSUT5 are the key proteins which involved in sucrose transport during grain filling.After the mutation of OsSUT3,the pollen viability of the ossut3 mutant plant decreased,which affected the fertilization at flowering stage of rice.As a result,the grain filling of ossut3 mutant plant delayed.After the mutation of OsSUT4,the pollen viability of the ossut4 mutant decreased.The grain filling was delayed and the supply of photoassimilates was insufficient of ossut4 mutant plant.Meanwhile,the grain weight of the ossut 4 mutant was lower than that of the wild type during the whole filling period.Eventually,the yield of ossut4 mutant decreased.The results illustrate that OsSUT3/4 are also vital proteins in the sucrose unloading of sink during grain filling.In conclusion,OsSUT 1/3/4/5 play certain roles in the grain sucrose unloading during rice filling.