| Cucumber(Cucumis sativus Linn.)is one of the main vegetable crops in China.However,the cucumber roots is distributed in the shallow area and sensitive to salted environment.Once it suffered salt damage,cucumber plant growth and development will be significantly inhibited,seriously affecting the yield and quality of cucumber.To some extent,exogenous sucrose can improve the plant’s resistance to stress,alleviate the pressure of stress,and can also be used as signal substance to regulate gene transcription and translation,but the mechanism of sucrose to relieve salt stress is not clear.The NAC is considered one of the important plant-specific transcription factors families,playing an important role in growth,development and stress resistance.In this article,NAC transcription factors of Cucumis sativus Linn.were studied.By employing Bioinformatics method and Real-time PCR,the characteristics of structure and biological function of NAC transcription factors was studied in this article.The main experimental results are as follows:In this paper,treatment with 50 mm / L salt stress after 3 days 0.4mm / L sucrose pretreatment or no pretreatment of cucumber seedlings was carried out.It is showed in this paper that the pretreatment of sucrose significantly promoted the development of lateral roots of seedlings,the dry weight of seedlings increased,the content of antioxidants.The content of malondialdehyde decrease significantly,indicating that sucrose Pretreatment improves the salt tolerance of cucumber seedlings.83 NAC-TF genes were identified by blasting NAM conserved domain against the entire Cucumis sativus Linn.genome.A total of 83 genes are located on 7 chromosomes,26 pairs of duplicate/triplicate genes were identified.a total of 125 amino acid sequences were clustered into 17 groups by different motifs between groups according to Ooka’s method(2003): NAM,ANAC11,ANAC3,ANAC63,ATAF,NAC1,NAC2,NAP,OSNAC22,OSNAC3,OSNAC7,SENU5,TIP,TREN,ANAC001.83 cucumber NAC protein amino acid sequence were analyzed on physical and chemical properties,the secondary structure,subcellular localization,conserved domain,motif,tertiary structure,GO function,cis-element in the promoter area.The NAC-TF of cucumber showed the characteristic of highly conservative N-terminal and diverted C-terminal in NAC transcription regions.58 NAC transcription factor exists in the nucleus in a higher probability than other organelles.In general,NAC proteins clustered in the same subgroups and share similar motif compositions,indicating functional similarities among members of the same subgroup.17 members of subgroups of NAM,ATAF,ANAC3 and ANAC11 were analyzed by real-time quantitative PCR.The results showed that the NAC transcription factors of the same subfamily had similar expression characteristics.Most of the other transcription factors were upregulated under sucrose pretreatment except that four NAC transcription factors of the ATAF subfamily,one of the ANAC3 subfamily,two of the NAM subfamily showed non-responsiveness to sucrose pretreatment.Only 5 NAC genes from NAM and ANAC11 subgroups were downregulated under salt stress,and the others were up-regulated in varying degrees.After pretreatment with sucrose,the expression level of most NAC transcription factors under salt stress was higher than that in direct salt treatment,and only three were lower than those of direct salt treatment.Tissue specificity analysis showed that eight of the 17 NAC genes had the highest expression level in the flower,six had the highest expression in the leaves,two had the highest expression in the fruit,and one had the highest expression level in the roots.The above predictive analysis and experimental results can help to further study the role of NAC transcription factor in the process of exogenous sucrose to alleviate salt stress. |
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