Molecular Mechanism Of Plant Rhizosphere Promoting Bacteria Serratia Marcescens LJL-11 To Alleviate The Salinealkali Stress Of Alfalfa

Saline-alkali stress restricts crop growth and yield.Plant growth promoting rhizobacteria(PGPRs)promote plant growth and development in various ways and resist the effects of saline-alkali stress on plants.Serratia marcescens LJL-11 can promote the growth of alfalfa(Medicago sativa L.)and alleviate the effects of saline-alkali stress.We used the Illumina Hiseq? 4000 sequencing platform to perform transcriptome sequencing on alfalfa(under saline-alkali stress)root tissue with or without S.marcescens LJL-11.Identification of key genes and metabolic pathways that play an important role in plant growth and stress tolerance under these conditions.To reveal the molecular mechanism of S.marcescens LJL-11 inducing alfalfa tolerance to saline-alkali stress.The results are as follows:1.Transcriptome sequencing of alfalfa was performed on 12 samples: three time points(0 h,6 h and 24 h),control and inoculation treatment.The Q30 quality of each sample was more than 90%,the GC content was about 41%,and a total of 320.93 M reads were obtained by sequencing.After quality control,77,788 Unigenes were obtained by de novo,with the average sequence length of 949 nt and the N50 value of 1325 nt.Homologous comparison with Arabidopsis and other seven legume species resulted in a total of 55,701(71.6%)Unigenes being annotated.2.GO annotation for Unigenes,a total of 42,607 GO entries were annotated.The structure of Unigenes was analyzed,43,952 CDS sequences were predicted and 11,527 SSR loci were identified.3.Differentially expressed genes(DEG)after inoculation with S.marcescens LJL-11 were screened according to gene expression,0H: 2,585,6H: 2,037 and 24H: 2,238.The GO function analysis of DEGs showed that the metabolic activities related to stress responses,defense responses and signal transduction were more enriched;MapMan annotation analysis of DEGs revealed important genes: HSP,ACO1,GH3,etc.;KEGG pathway enrichment analysis was performed on DEGs,which involved plant hormone signal transduction,nitrogen metabolism and MAPK signaling pathway-plant,etc.Furthermore,the functional genes extracted from DEGs are mainly involved in stress response,ion balance,plant hormones and nutrient metabolism,such as: CHS,GH3,SAUR,ACO and MYC2.These important functional genes are closely related to the molecular mechanism of S.marcescens LJL-11 inducing alfalfa tolerance to saline-alkali stress.4.The gene expression patterns of 12 DEGs were verified by Quantitative Real-Time PCR(qRT-PCR),and the correlation analysis was performed with the transcriptome results.The results indicated that the qRT-PCR results and the transcriptome results were consistent.5.Analyzed of Medicago sativa GH3 gene family,and identification of 14 MsGH3 members.According to the grouping information of Arabidopsis thaliana,MsGH3 was divided into 4 groups,including Group ?(MsGH3.1~MsGH3.3),Group ?(MsGH3.4~MsGH3.6),and Group ?(MsGH3.7~MsGH3.14).Analyzed the conserved domains of MsGH3 by the CDD database,and revealed that they all contained the GH3 domain.Prediction of the protein sequence of Ms GH3 gene and analyzed of its basic physical and chemical properties.Analyzed of MsGH3 expression pattern in the transcriptome,and they were up-regulated at 3 time points after inoculation with S.marcescens LJL-11.Calculated the ratio of nonsynonymous and synonymous(Ka/Ks)of the MsGH3 genes,the result indicated that the Ms GH3 genes have been strongly purified during the evolution process and the genes have a conservative function.