Exogenous Sucrose Enhances The Drought Tolerance Mechanism Of High-expression Transgenic Maize C₄ Type Pepc Rice

To reveal the role of sucrose in plant drought response signal transduction,high expression of transgenic maize C₄ phosphoenolpyruvate carboxylase?PEPC?gene?C₄-pepc?rice?PC?and wild type“Kitaake”?WT for short?was used as material to analyze the effects of different concentrations of sucrose on seed germination during seed germination under the simulated drought treatment of 10%polyethylene glycol 6000?polyethylene glycol-6000,PEG-6000?.The optimum concentration of sucrose for promoting PC seed germination under drought treatment was 3 mmol/L.On the basis of this,further application of 3 mmol/L sucrose under the treatment of 10%PEG simulated drought or natural drought in seedling stage and tillering stage.Further explore the physiological and biochemical mechanisms of sucrose-induced drought response in PC rice at the plant level.The main results are as follows:1.The seeds harvested in the same year,WT and PC were used as materials.After disinfection and soaking,10%PEG-6000 simulated drought treatment,and set0/0.3/3/30/150 mmol/L sucrose treatment to detect seed germination coefficient and radicle,germ length ratio,total soluble sugar and sugar component content,soluble protein content,endogenous C₃-pepc in seed,exogenously introduced C₄-pepc gene expression and expression of SnRK1s subfamily gene.The results showed that compared with WT,the application of 3 mmol/L sucrose significantly increased the germination rate and germination potential of PC seeds and improved the normal development of PC radicle and germ.At the same time,the endogenous sucrose content in PC buds was significantly up-regulated,and the content of soluble sugar and soluble protein in osmotic adjustment substances also increased significantly.It is noteworthy that the expression of endogenous C₃-pepc gene was significantly increased in PC buds under simulated drought treatment alone,but the application of 3 mmol/L sucrose treatment down-regulated the expression of endogenous C₃-pepc gene and significantly up-regulated the exogenous source.The expression of C₄-pepc was introduced,and the expression of SnRK1s subfamily gene was significantly increased in PC rice after sucrose treatment.Correlation analysis further confirmed the germination parameters and physiological indexes of PC seeds and the expression of C₄-pepc gene and SnRK1s subfamily gene.Related.It was shown that after 10%PEG-6000 simulated drought treatment,the application of 3 mmol/L sucrose changed the concentration of endogenous sucrose in PC,and the expression of exogenously introduced C₄-pepc gene was induced by the expression of sugar signal SnRK1s family gene.The content of osmotic adjustment substances such as soluble sugar and soluble protein in seeds increased,which was beneficial to alleviate the inhibition of PC seed germination by drought stress.2.To further reveal the application of low-concentration sucrose to the drought-tolerant regulation mechanism of PC rice plants,using WT and PC rice as materials,after hydroponic and pot experiment,after 10%PEG-6000 simulated drought or natural drought treatment,3 mmol/L sucrose was applied to determine the relative water content,chlorophyll content,photosynthetic parameters and physiological indexes,SnRK1s subfamily and SnRK2s subfamily related genes and drought related downstream genes and transcripts.The results showed that the application of sucrose significantly improved the degree of curling of PC leaves under drought treatment,significantly increased the relative water content and chlorophyll content of PC leaves,and greatly improved the net photosynthetic rate of PC,but the effect on WT was not obvious.Further detection showed that the sucrose content in PC increased significantly,the total soluble sugar content and proline content increased significantly,the sucrose transporter gene expression increased significantly,the C₄-pepc gene expression was up-regulated,and the SnRK1s subfamily gene expression increased and ABA-induced expression of the SnRK2s subfamily gene was significantly up-regulated,while down-regulating the expression of downstream genes and transcripts associated with drought.Correlation analysis showed that the net photosynthetic rate of PC was correlated with the expression of drought-related transcripts OsbZIP23,OsbZIP46 and NAC6.Exogenous sucrose increased the sucrose content in PC,and the content of endogenous sucrose and soluble sugar in PC were significantly correlated with C₄-pepc expression.In addition,endogenous sucrose content correlated with OsSUT1 and OsSUT4expression,and was significantly associated with SnRk1s and SnRk2s gene expression,respectively.It can be seen that the introduction of exogenous sucrose increases the endogenous sucrose concentration of PC by up-regulating the endogenous sucrose transporter family gene of PC rice,thereby further increasing the content of soluble sugar in PC and up-regulating the expression of C₄-pepc gene and energy metabolism.The expression of the SnRK1s subfamily gene shows the signal characteristics of endogenous sucrose.Under drought conditions,sucrose signal may also interact with ABA signal to participate in the regulation of drought-related downstream genes and transcription factors by SnRK2s subfamily gene,and finally maintain high relative water content and chlorophyll content of PC under drought stress.Its photosynthesis is stable,thereby enhancing the drought tolerance of PC rice plants.