Analysis Of Transcriptome Expression Profile Of Maize Seedling Roots Under Na₂CO₃ Stress

Saline-alkali stress includes neutral salt stress such as Na Cl and basic salt stress such as Na₂CO₃.The stress mechanism of neutral salt on plants has been widely reported,but there are few studies on the stress mechanism of basic salt.Maize is a moderately sensitive crop to salt and alkali,particularly severe in maize seedling.Maize roots were initially in response to the saline-alkali stress.Transcriptome can systematically revel gene expression and interaction so as to analysis the resistance mechanism to salt-alkali stress.These are the theoretical basis of breeding tolerant varieties.Therefore,it is of great significance to analysis the response mechanism of maize roots to basic salt stress by the digital gene expression profile and discove related genes.In this study,the alkaline tolerance of 200 maize inbred lines were identified.Zheng58 tolerant to alkaline and Chang7-2 sensitive to alkaline were used as experimental materials,and maize roots at the v3 stage were stressed for 5 h and 24 h respectively in 100 mmol/L Na₂CO₃（p H=11.2）and ultrapure water as control.The transcriptome sequencing was completed by Illumina platform,and the results were systematically studied by bioinformatics,and verified by fluorescence quantitative PCR.The main results were as follows:（1）In this study,the seedling condition and alkaline tolerance of 200 inbred lines at the v3 stage were measured in 100 mmol/L Na₂CO₃.Two hundred inbred lines were divided into 5 groups by systematic clustering,in which the materials with high tolerance,medium tolerance,sensitivity and high sensitivity were 8,19,32,75 and 66,respectively.Based on the aboved results and the identification of the seedling stage,Zheng58（A）with high tolerance and Chang7-2（B）with high sensitivity were used to the further research of expression profile sequencing.（2）The results of the expression profile sequencing showed that with CK as the control,there were 5,863 and 8,012 differentially expressed genes（DEGs）in alkali-resistant material（A）and 5,065 and 11,421 DEGs in alkali-sensitive material（B）.（3）The analysis of GO enrichment found that materials A and B had 4638,6285,4077 and 9111 DEGs for 5 h and 24 h respectively,and 56 functions were annotated by the aboved different materials.The significantly enriched GO terms mainly include biological processes such as abscisic acid transport and signal pathway activated by abscisic acid,cell components such as plastid membrane and inherent components of organelle membrane,and molecular functions such as glutathione transferase activity and magnesium ion binding.（4）The analysis of pathway enrichment found that the significantly enriched pathway of two materials were plant MAPK signal pathway and plant hormone signal transduction.Combined some significantly enriched pathway with DEGs,the highly expressed genes in the significantly enriched pathway were annotated as protein phosphatase 2C family protein and ethylene receptor homologue 2 precursor.（5）Transcription factors analysis showed that there were 54 transcription factors（TFs）in all differentially expressed genes,which could be divided into 10 TFs families,included AP2,b HLH,b ZIP,C2H2,EIL,ERF,GRAS,MYB,NAC and WRKY.（6）In this study,18 genes related to alkali-resistant were screened,including 10DEGs with significant differential expression in GO term,5 DEGs with specific expression in alkali-resistant materials in pathway enrichment analysis,3 DEGs with significant differential expression in transcription factors.Eight genes were used for the verification of q RT-PCR,which included Zm00001d028154,Zm00001d029744,Zm00001d002266,Zm00001d004762,Zm00001d006106,Zm00001d024853,Zm00001d040468,and Zm00001d0344538.The expression of Zm00001d028154,Zm00001d029744,and Zm00001d040468 were highly expressed in alkali-resistant materials,and showed a significant change among different time points.The expression level in alkali-sensitive materials is low and there is no obvious difference among different time points.These genes may play an important role in alkali stress.