The Major Metabolic Pathways At Maize Developing Young Tassel In Response To Drought Stress And Identification Of Drought-tolerant Candidate SNAC Genes

Drought is one of the major environment stresses limiting maize production. The identification of drought-tolerant genes and metabolic pathways are essential to enhance the stability of maize production. In our research, ten inbred lines commonly used in China were taken to study drought-responsed genes expression and their metabolic pathway at maize developing young tassel by using RNA-sequencing technology under water-stressed and well-watered conditions, respectively. And drought-tolerant SNAC genes were further screened and identified. The main results were as following:(1) Transcriptome sequencing of ten inbred lines under water-stressed and well-watered conditions showed that average 46,920,265 clean reads were generated, and average 32,491,972 reads were uniquely matched to maize reference genome. Averagely,29,582 expressed genes were scranned in twenty samples, which 1,902 difference expression genes (DEGs) in developing tassel were identified in response to drought stress (P?0.001, FDR? 0.001,|log2Rato|?1).(2) The GO enrichment analysis of DEGs were filtered to 286 specific biological terms (P<0.05). Of them,129 terms were identified to be classified to cellular component ontology, 101 terms to biological process ontology and 56 terms to molecular function ontology (P<0.05).3,121 DEGs were predicted their specific molecular functions by GO analysis.(3) The major drought-responsive metablic pathway at maize developing tassel were identified as following:transport regulation, energy metabolism, carbohydrate metabolism, lipid metabolism, biosynthesis of secondary metabolites, metabolism of terpenoids and polyketides.'RNA transcript and mRNA surveillance pathway'were significantly enriched in transport regulation,'photosynthesis, photosynthesis-antenna proteins, nitrogen metabolism' were significantly enriched in energy metabolism,'galactose metabolism and pentose phosphate pathway'were significantly enriched in carbohydrate metabolism,'carotenoid biosynthesis, limonene and pinene degradation, diterpenoid biosynthesis'were significantly enriched in metabolism of terpenoids and polyketides,'flavonoid biosynthesis, anthocyanin biosynthesis, etc'were significantly enriched in biosynthesis of other secondary metabolites, genes of lipid metabolism were significantly enriched in' fatty acid elongation'to regulate 'cutin, suberine and wax biosynthesis'(P<0.05).(4) Under drought stress, DEGs of exon-junction complex (EJC) relative genes were identified in transcriotion process to play an important role in defending drought stress by regulating RNPS1 and SRm160 proteins. Invertase and 6-phosphofructokinase in carbohydrate metabolism including mnl, ivr2, GRMZM2G095725, GRMZM2G017991, GRMZM2G398807 played an important role in carbohydrate metabolism to response drought in developing tassel.3-ketoacyl-CoA synthase and fatty acyl-CoA reductase in lipid metabolism of developing tassel including GRMZM2G409312, GRMZM2G062718, mshl played an important role in lipid metabolism to response drought in developing tassel.(5) By analyzing the transcriptome sequencing data of drought-tolerant line'Tie7922', three NAC family genes ZmNAC010312 (P=2.99×10-28), ZmNAC080308 (P=1.11×10-10) and ZmNAC030295 (P=1.61×10-21) were significantly identified up-regulated expression in developing tassel under drought stress. The same protein motifs were found between the three genes and known drought- or dehydration-tolerant genes in rice. They were predicted as drought-tolerant responsive candidate genes in SNAC (stress-responsive NAC) subfamily.