Mechanism Of Improvement Of Drought Resistance Of Rice By Exogenous Glutamic Acid

As a major grain crop in China,rice（Oryza sativa L.）accounts for about 1/3 of the sown area of grain crops and 40%of the total grain yield.The growth and development of rice needs to consume a lot of water resources.Drought will seriously affect the normal growth of rice,which also restricts the sustainable development of rice production in China.As an induced defense compound,Glu is applied before stress to achieve the defense alert of induced plants,so as to reduce the tolerance of plants under specific stress,which has important practical significance for realizing the high and stable yield of important food crops such as rice.The main results are as follows:1.Exogenous Glu significantly affects the growth of rice seedlings.The rice seedlings were continuously cultured with normal nitrogen（1.25mM NH₄NO₃）,nitrogen-deficient（0 mM NH₄NO₃）and different concentrations of glutamic acid（0.1,0.625,1.25,2.5,5 mM）nutrient solution,and the difference was detected after 26 days.Root length,seedling height,root fresh weight,shoot fresh weight and SPAD value of rice seedlings under nitrogen supply treatments.The results showed that,compared with the control,rice cultured with 0.625 mM and above glutamic acid had significantly increased seedling height,root fresh weight,shoot fresh weight and SPAD value,while root length was significantly inhibited,adding 0.1 mM Compared with the rice without nitrogen source,there is no significant difference between the rice with Glu and the rice without nitrogen source.It can be seen that a certain concentration of Glu can be used as a nitrogen source to support the normal growth of rice.2.Exogenous Glu pretreatment improves the drought resistance of rice at seedling and tillering stages.The rice plants at seedling stage were pretreated with normal nitrogen（control）and different concentrations of Glu（2.5 mM and 5 mM）for 48 h,and then 20%PEG 6000 was used to simulate drought stress.Plant survival rate and fresh weight;rice at the tillering stage was pretreated with different concentrations of glutamic acid and then subjected to natural drought,and the plant mortality was counted after recovery.The results showed that compared with the control,Glu pretreatment could significantly reduce the degree of wilting of rice,significantly improve the recovery ability and survival rate of rice after drought,and improve the ability of rice biomass accumulation,thereby improving the drought resistance of rice.3.Effects of exogenous Glu pretreatment on drought resistance physiology of rice at seedling and tillering stages.The rice seedlings and tillering stages were pretreated with normal nitrogen（control）and different concentrations of Glu（2.5 mM and 5 mM）for 48 h,respectively,and then the rice seedlings were treated with 20%PEG 6000 to simulate drought stress and control.Rice was subjected to natural drought at the tillering stage,and the shoots of rice seedlings were sampled to detect drought resistance-related physiological functions such as free proline,malondialdehyde,POD enzyme activity,and CAT enzyme activity of rice at different time points of glutamate pretreatment and drought stress.The results showed that the content of malondialdehyde in rice pretreated with Glu was significantly decreased,and the activities of free proline,POD enzyme and CAT enzyme were significantly increased.The water loss rate statistics and ROS staining of rice at the tillering stage showed that Glu pretreatment could significantly reduce the leaf water loss rate and the outbreak of reactive oxygen species,thereby improving the drought resistance of rice.4.Transcriptome detection of differentially expressed genes in rice seedlings after Glu pretreatment.The rice at seedling stage was cultured with normal nitrogen source（control）and treated with Glu（5 mM）,and samples were taken for transcriptome sequencing 12 h after treatment.Statistics of the differential genes between the two treatments showed that239 genes were up-regulated and 147 genes were down-regulated in the Glu treatment group.KEGG enrichment found that 12.64%of the differential genes were enriched in the plant hormone signal transduction pathway,and 32.18%of the differential genes were enriched.Enriched in the biosynthetic pathway of secondary metabolites,47.13%of the differential genes were enriched in the metabolic pathway,and 13.79%of the differential genes were enriched in the plant-pathogen interaction pathway.The differential genes related to the jasmonate pathway were verified by qPCR,and it was found that the expression of OsHI-LOX,OsAOS2,OsbHLH148 and OsJAZ10 could be significantly increased after glutamate treatment.5.Wide target metabolome to detect differential metabolites in rice seedlings treated with Glu.The rice at the seedling stage was cultured with a normal nitrogen source（control）and treated with Glu（5 mM）,and the samples were sampled for metabolic sequencing 12 h after the treatment.Compared with control rice,13 differential metabolites were up-regulated and 18 differential metabolites were down-regulated in Glu-treated rice.KEGG enrichment found that 83.33%of the differential metabolites were enriched in the metabolic pathway,50%of the metabolites were enriched in the secondary metabolite biosynthesis pathway,and 25%of the metabolites were enriched in the phenylpropane biosynthesis pathway.6.Glutamate activates jasmonate signaling pathway.The aboveground parts of rice seedlings were sampled and the expression of rice resistance-related genes at different time points of glutamate pretreatment and drought stress were detected.The results showed that glutamate induced calcium signaling pathway related genes OsCam1-1,OsCML4,OsCPK4,JA synthesis related genes OsAOS2 and JA signaling pathway related genes OsHI-LOX,OsJAZ8 were induced to express,glutamate activated calcium signal and jasmonic acid signal.Jasmonic acid synthesis mutant cpm2（AOC out-of-function）was used to detect the role of jasmonic acid signaling pathway in Glu-induced drought resistance in rice.That is,normal nitrogen（1.25 mM NH₄NO₃）and different concentrations of Glu（2.5 mM and 5 mM）were used to pretreat rice at tillering stage and then natural drought.The results showed that under drought conditions,Glu pretreatment did not significantly improve the drought resistance of cpm2,and the improvement of rice drought resistance by Glu pretreatment partly depended on the jasmonic acid signaling pathway.This study clarified that glutamate pretreatment can improve the drought resistance of rice,and deeply analyzed the mechanism of glutamate pretreatment to improve the drought resistance of rice from the level of transcription and metabolism,which provides a new idea and way to solve the problem of rice drought.