| Bread wheat(Triticum aestivum L.)is one of the most important crops to provide nutrition and energy for human beings,which ensures the food security of the world.However,the yield and production of the wheat are challenged by incerasing limits,such as shortage of land resources,climate change and population growth.As the result,it’s yield and production have been no longer to meet the needs of human beings.Root is an important organ of plants for absorpting nutrition and water,and the study of root system is believed as the key to the next Green Revolution.Thus,it is necessary and meaningful to fine-tuned root growth in soil to optimize crop yield and quality.Auxin is one of the most important hormones which can regulate many biological processes,especially in root growth and lateral root development.Therefore,we treated the wheat roots with two different concentrations of auxin(1 and 50 μM IAA)and comprehensively revealed the expression,interrelationship and regulatory network of auxin responsive genes in wheat roots by the transcriptome sequencing analysis,GO and KEGG analysis as well as WGCNA analysis.In addition,we focused on b ZIP transcription factors for further study according to the results,and their phylogenetic classification,gene conserved motif and gene structure were carried out to speculate the different molecular mechanisms of auxin responsive TabZIPs in different subgroups.Finally we verified gene function of the cadidated gene TabZIP6D＿147in hy5 mutant by transgenic method.Taken together,the main results of the study are as follows:1.The RNA-seq results showed that a total of 8747 differentially expressed genes(DEGs)were identified under IAA treatments.There were 308 upregulated and 326 downregulated DEGs under 1 μM IAA treatment,while 6118 downregulated and 2333 upregulated DEGs were identified under 50 μM IAA teratment.The expression of most DEGs were downregulated and the mode of regulatory wheat root development under 50 μM auxin was more subtler and complexer.2.GO enrichment showed that there were similar significantly enriched GO terms after the both of treatments,and the KEGG analysis also showed that there were similar enriched pathways,for example,carbohydrate metabolism,glutathione metabolism,amino acid metabolism and energy metabolism.It was suggested that higher concentrations of auxin might have similar molecular mechanisms in regulating wheat root development.In addition,the inhibitory effect of 1 μM IAA was reflected in glycolysis/gluconeogenesis,platinum drug resistance,valine,leucine and isoleucine degradation,and glutathione metabolism pathways.However,the enrichment of carbon metabolism,phenylpropanoid biosynthesis and glutathione metabolism pathways under 50 μM IAA treatment highlighted the stress effects of high concentrations of auxin on wheat roots.3.According to the WGCNA,there were a total of 22 auxin responsive hub genes and the protein kinase might be as regulatory center genes to respond to auxin treatments.Higher concentrations of auxin activated multiple detoxification chains of wheat roots,including the multiple cytochrome P450 involved in phaseIreaction,glutathione S-transferases and UDP-glycosyltransferases involved in phase II reaction,and metal transport/detoxification protein family members involved in phase III reaction,such as oligopeptide transporter(OPT),multidrug and toxic compound efflux transporter family genes(MATE)and iron transporter(Ccc1).In addition,the genes related to photosynthesis and glucose metabolism and transcription factors such as b ZIP,Dof and AP2/ERF also responsed to auxin to regulate wheat roots growth and development,indicated that wheat might adapt to higher concentration auxin treatments by maintaining a lower level of root growth and development.4.A total of 176 TabZIP genes were identifed from the wheat genome by bioinformatics methods.Phylogenetic classification,gene conserved motif and gene structure analysis indicated that TabZIPs were divided into 9 subgroups.Based on the transcriptomic data,22 auxin responsive TabZIPs were identified,and only 4 TabZIPs were response to 1 μM IAA,and their expression were all downregulated.Besides,there were 21 TabZIPs were response to 50 μM IAA,including 17 downregulated and 4 upregulated TabZIPs.The 22 auxin responsive TabZIPs were mainly in groups 1,4,5,6,7,8,9 and might play different roles in ABA,GA,light and sugar signalling pathways.Therefore,further verifications of the functions of auxin responsive TabZIPs could make the network of wheat root regulation more comprehensive.5.Over-expression of TabZIP6D＿147(one of the downregulated auxin responsive TabZIPs under both 1 μM and 50 μM IAA)in Arabidopsis hy5 mutant recovered the root to that of the Ws,suggesting that downregulated TabZIP6D＿147 plays a negative role in wheat root development and auxin signalling pathway.The study provides theoretical basis and candidate genes for improving wheat roots by transgenic methods. |
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