Differential Gene Expression Profiling Of Maize Roots Under Saline And Alkali Stresses

Saline-alkali stress has an important impact on crops. It is significant tounderstand plant tolerance mechanism to salinity for the nurture of salinity plantvarieties. Saline-alkali stress includes neutral salt stress such as NaCl and alkaline saltstress such as Na₂CO₃. Na₂CO₃stress is the combination of sodium stress, high pHvalue stress and carbonate stress. Previous studies on plants response to Na₂CO₃aremainly concentrated on the response to the substance as a whole. However, howplants respond to these three stress factors respectively, especially carbonated stresshas rarely been reported. Therefore, plant response mechanisms of the three stressfactors are of great significance for resolving the response mechanism of sodiumcarbonate stress conditions.Maize is an important food, feed and cash crops. Saline-alkali stress has a strongimpact on maize production which is particularly severe in maize seedling. In addition,the saline-alkali condition stresses maize roots initially. Therefore, seedlings maizeroots are suitable to be used as the material of the study on salinity stress mechanism.In this study, we stressed the maize seedling roots of three-leaf stage for fivehours under100mM of NaCl,50mM of Na2CO3（pH11.39）,1.28×10^-4mM NaOH（pH11.39） stresses, with ultrapure water treatment as control. We explored the geneexpressing profiling using digital gene expression sequencing method, which is basedon the new generation of sequencing technology. The sequencing data were verifiedby quantitative PCR method. The results are as follows: 1. We detected about27,000genes expressed in each sample. It is about83%ofthe reported genes in the genome. And all gene expression ranged as a normaldistribution.2. We found the number of genes up-regulated under stress conditions in sodiumchloride, sodium carbonate and sodium hydroxide were1865,3087and395respectively, and the number of genes down-regulated under stress conditions insodium chloride, sodium carbonate and sodium hydroxide were1361,5232and339respectively. We assume the1937, and the214commonly differentially expressedgene in Na₂CO₃and NaOH stressed samples responded to high pH value stress. Alsothe5818genes that exclusively expressed in Na2CO3stressed sample respond tocarbonate stress.3. By GO enrichment analysis, we found7GO terms that significantlyup-regulated in all the three16in the sodium chloride and sodium carbonate stressconditions and9in sodium carbonate and hydrogen sodium oxide stress conditions.4. By pathway enrichment analysis, we found2KEGG pathways thatsignificantly enriched in all the three stress conditions which were ABC transporterprotein and Nitrogen metabolism, and pathways enriched in both sodium chloride andsodium carbonate stress samples which were Plant-pathogen interaction and甜菜素biosynthesis pathway. We also found the pathway that significantly enriched only insodium carbonate stress sample which is Ascorbate and aldarate metabolism.5. We verified the digital gene expression sequencing results by quantitative PCRmethod using20significant differentially expressed genes that were randomlyselected as samples. The result showed that70%of the gene expression tendency wasthe same between digital gene expression results and quantitative PCR results. Thusthe expression profiles of the sequencing results were confirmed. Based on the results above, we acquired genes, GO terms and pathways thatrespond to carbonate stress, sodium stress, high pH value stress and all stresses aboverespectively. Plant response network toward saline-alkali stress is discussed to providesome theoretical basis for further study on salt tolerance gene, and to reveal themolecular mechanisms of plant responses to stress. It also provides a number of generesources for the study of plant response to carbonate stress in the future.