Seasonal Expression Regulation Of Xylem Development Of Populus Davidiana ×P.bolleana And Preliminary Analysis Of PdbbZIP1 Gene Function

Xylem development is the key process of wood formation in woody plants.In order to study the molecular regulation mechanism of Populus davidiana ×P.bolleana xylem development,we identified the key genes regulating the development of Populus davidiana ×P.bolleana xylem.In this study,the expression profile analysis and differential expression gene identification of the xylem development of Populus davidiana ×P.bolleana at six different time points in a growing season were carried out.One of the differentially expressed genes was selected for preliminary analysis of gene function.The results of the study are as follows:The slide-away sections were used to analyze the xylem of Populus davidiana ×P.bolleana at six developmental time points from mid-April to early August,and the sections were stained with Safranin and Fast Green.Microscopic observations showed that at S1,the xylem had not yet developed;at S2,the xylem began to form;at S3,the developing xylem cells divided rapidly,the xylem expanded rapidly,and most cells began to synthesize secondary cell walls.These procedures continued until S5,and the xylem expansion rate was slightly reduced.There is no obvious microscopic difference between S5 and S6,and the formation of late wood was observed.Transcriptome sequencing was used to analyze xylem samples from six periods.After the transcriptome is assembled and annotated,differentially expressed genes(DEG)are identified,and GO enrichment analysis,KEGG pathway analysis and DEG expression analysis are performed on each sample.The results showed that a total of 14,890 genes were differentially expressed in the six stages.In the comparison of different stages.GO pathways related to cell wall biosynthesis and plant hormones are significantly enriched,and KEGG pathways related to "phenylpropane biosynthesis","plant hormone signal transduction" and "starch and sucrose metabolism" in DEG are significantly enriched.Enriched.The DEGs related to cell expansion,polysaccharide metabolism and synthesis,lignin synthesis,transcription factors and hormones were identified.Six bZIP family differential genes were found from the transcriptome,and one of the members with higher expression and the most significant difference in expression was selected for cloning and named PdbbZIP1.The results of bioinformatics analysis showed that the PdbbZIP1 coding region sequence is 945 bp in length,encodes 314 amino acids,and has the domain of the bZIP family.The results of phylogenetic analysis showed that it had the closest homology to the AT2G31370.3 gene in Arabidopsis,and research showed that it was involved in drought and salt stress responses.We speculate that the PdbbZIP1 gene has similar functions.The fluorescence quantitative PCR analysis of its expression pattern under abiotic stress treatment showed that the PdbbZIP1 gene responds to salt and drought induction.The rapid gene function analysis of PdbbZIP1 was carried out by transient infection method,the overexpression vector and suppression expression vector of PdbbZIP1 gene were transiently transformed into Populus davidiana ×P.bolleana,and its drought and salt tolerance function was identified through physiological index determination.And verify the transcriptional activation domain of PdbbZIP1 gene to verify the existence of self-activation domain.The results showed that the PdbbZIP1 transcription factor has transcriptional activation activity in yeast,and its transcriptional activation domain is located within the 223-342 bp of the N-terminal.The transgenic overexpression line under the stress of 200 mM NaCl and 300 mM mannitol has stronger salt tolerance and drought resistance than the wild type Populus davidiana ×P.bolleana.It further shows that PdbbZIP1 plays an important regulatory role in the salt and drought stress resistance of transgenic aspen poplar.The molecular mechanism of its involvement in the environmental response of xylem development and abiotic stress resistance needs further study.This study analyzed the seasonal molecular regulation pathways of xylem development in Populus davidiana ×P.bolleana,and identified important xylem development regulation genes,which will increase the understanding of the molecular regulation of wood formation and provide potential targets for genetic manipulation.