Function Of OsEXPB1 Gene Under Drought Stress And Comparison Of The Promoters Activity In Transgene Vector

Part oneRice is one of the most important crops in China. Its yield is largely affected by many environmental factors, such as drought. Developing drought-tolerant rice cultivar by transgenic technique is of great significance for agronomic production and water saving.EXPANSIN genes play important roles in plant growth, such as loosening the cell wall and promoting cell growth. In our study, Os03g0106500 (OsEXPB1) gene was identified to be a down-regulated gene in expression level under the drought stress during reproductive stage. Its function in drought response was further studied here.The promoter sequence of OsEXPB1 was cloned by Polymerase Chain Reaction (PCR) technique and fused into a GUS reporter vector. GUS staining of the transgenic lines indicated that the promoter was active in young vegetative tissues and developing florets, especially pollens. Quantitative reverse transcriptional (qRT)-PCR results were consistent with the results of GUS staining. OsEXPB1-overexpressing line OE-20 was taller and produced more florets than wild type plants, and also more resistant to drought stress at seedling and reproduction stages. Both RNAi and mutant plants were extremely sensitive to drought stress, and the root growth was also delayed. These evidence suggest that OsEXPB1 is very important for the development as well as drought response of rice plants.Part twoPromoter controls gene expression in organisms. CaMV 35S, UBIQUITIN and ACTIN promoters are the most widely used promters in plant genetic engineering. In dicotyledonous plants, CaMV 35S is effective in driving gene overexpression in vegetative tissues, but not in reproductive tissues. In monocot plants,35S is rarely used. Instead, the maize ubiquitin gene promoter and rice actin gene promoter are used more commonly. They are used for driving gene overexpression in vegetative tissues such as leaf, root and stem. So far, the knowledge about the activities of these promoters in monocot plant florets is not available, especially in rice reproductive tissues.During the research process in our lab, it is very often to construct transgenic vectors for overexpression of target genes, particularly transgenic vectors for gene overexpression in rice florets. To obtain an overview of the the activities of the most commonly used promoters, we compared the activities of 35S, UBI and ACTIN promoters in vegetative and reproductive tissues of rice by GUS reporter transgenic lines. The results showed that all of them have very strong activities in vegetative tissues, but the activity of 35S promoter is relatively weak and ununiform in rice florets. Both UBI and ACTIN promoters can drive GUS overexpression in florets, but the activity of ACTIN promoter is more stable and uniform. Our results provide important basis for selecting promoters for driving overexpression of foreign genes in the reproductive organs of crops.