Functional Study Of Maize NAC Transcription Factor ZmNAC19

Maize（Zea mays L.）is an important food and forage crop,which is planted all over China.In the growth and development of maize,lodging often occurs under the action of wind,and various diseases seriously affect the yield and quality of maize.Studies have shown that the mechanical strength of plant cell wall is related to the disease resistance and lodging resistance of plants,and NAC transcription factors play an important role in the formation of plant secondary wall.A NAC transcription factor gene ZmNAC19 was screened out from maize in the laboratory in the early stage,which was highly expressed in leaves,and was introduced into Arabidopsis thaliana through agrobacterium-mediated transfer,and t1-generation positive plants with overexpression of ZmNAC19 in Arabidopsis were obtained.In order to further explore the biological functions of ZmNAC19 gene,we screened arabidopsis thaliana T2 generation homozygous plants with overexpression of ZmNAC19 gene and observed their phenotypes.The ultrastructure of the cell wall of Arabidopsis thaliana overexpressed ZmNAC19 gene was observed by transmission electron microscopy.Finally,transcriptome sequencing was used to analyze the differentially expressed genes in arabidopsis thaliana overexpressed ZmNAC19 compared with wild-type plants,and the functional annotation and metabolic pathway analysis of the differentially expressed genes were conducted to clarify the regulatory mechanism of ZmNAC19 in regulating cell wall development and secondary wall formation.The main results are as follows:Phenotypes of T₂ generation homozygous plants and wild-type Arabidopsis overexpressing ZmNAC19 gene were observed.Phenotypic comparison showed that compared with wild-type arabidopsis thaliana,the rosette leaves of ZmNAC19 overexpressed Arabidopsis thaliana showed curl shape,and the petiole became thicker,and the leaf length and leaf surface area increased.To look at the plant flowers moss,ZmNAC19 gene overexpression of arabidopsis flower more thick moss,in the absence of support measures can grow upright,suggests ZmNAC19 a gene expression influenced the growth of Arabidopsis leaves and flowers moss,overall diameter increases,the intensity of the characteristics of the larger,that the gene may be involved in the regulation of cell development.Ultrastructural observation showed that the cell wall of Arabidopsis flowering moss overexpressed by two ZmNAC19 genes was significantly thickened compared with that of wild type arabidopsis.The secondary wall of arabidopsis flowering moss showed uneven thickening in the inner cell wall,indicating that the accumulation of secondary substances was significantly increased.Compared with wild-type Arabidopsis,the cell wall of the petiole was significantly thickened in Arabidopsis with overexpression of ZmNAC19 gene.However,the accumulation of secondary substances in the inner side of petiole cell wall did not increase significantly,which may be caused by the inactivity of secondary metabolism in petiole under normal growth state rather than the exuberant secondary metabolism in flower moss.Transcriptome sequencing analysis showed that there were 3250 differentially expressed genes between ZmNAC19 transgenic Arabidopsis and wild-type Arabidopsis,including 970 up-regulated genes and 2280 down-regulated genes.GO annotation analysis was performed on these differentially expressed genes,and the genes with specific expression were all involved in a total of 30 GO term secondary classifications under the three categories of biological process,cell component and molecular function.In the category of biological processes,the number of genes annotated with protein phosphorylation was the largest.Among cell components,the number of genes annotated to the membrane component was the largest.The number of genes annotated to ATP binding was the largest among the molecular functional categories.KEGG annotation analysis was performed on DEGs of ZmNAC19 and WT,and these DEGs were annotated on three branches of metabolic pathway:metabolism,genetic information processing and environmental information processing.DEGs of ZmNAC19 and WT were enriched in 48 pathways through KEGG pathway.When Pvalue was less than 0.15,metabolic pathway and biosynthesis pathway were significantly enriched.In enrichment to these pathways,plant pathogen interaction,biosynthesis,benzene propane phagosome,metabolic pathway,homologous recombination,metabolism of fatty acids,fatty acids,elongation,fatty acid biosynthesis,cutin berberine and wax biosynthesis,metabolism of biotin,unsaturated fatty acid biosynthesis,the biosynthesis of secondary metabolites.These results suggest that ZmNAC19 may regulate the thickening of secondary wall by regulating the biosynthesis of secondary metabolites（lignin,cellulose,etc.）,and affect the generation of a variety of biological metabolites in plants.