Functional Analysis Of OsAP21, An AP2/ERF Transcription Factor In Rice (Oryza Sativa L.)

Drought, high-salinity and low temperature are commonly adverse environmental conditions. These stresses were given to more attention during recent years. Plants have evolved to perceive different stress signals from their surroundings, to integrate them and to respond to these different stresses by modulating the expression of related genes in environmental stress conditions. Transcription factors play vital roles in stress signal transduction, gene expression modulation and phase transition during plant development. Till now, a number of transcription factor families have been found involving in plant stress responses, and each contain a different type of DNA-binding domain, including AP2/ERF, MYB, WRKY, NAC and bZIP and so on. AP2/ERF is an important transcription family which related to plant development and physiology. In this study, a transcription factor gene OsAP21 belong to AP2/ERF family ERF subfamily from rice was analysed function.Based on the cDNA sequences of OsAP21 gene, a complete open reading frame of OsAP21 was amplified from IR36 rice varieties. The full-length cDNA of OsAP21 has a 687bp open reading frame (ORF). It has a conserved DNA binding domain present in a large family of AP2/ERF and contains a basic region in its C-terminal that might function as a nuclear localization signal and two acidic regions on either side of the AP2 domain. The results of RT-PCR analysis for O. sativa IR36 exposed to various treatments indicated that the mRNA of gene OsAP21 was induced by ABA and abiotic stress. We show here overexpression of OsAP21 resulted in a dramatic increase in tolerance to salt stress and drought stress in transgenic Arabidopsis plants.Analysis of transgenic plant suggested that over-expression of OsAP21 in transgenic Arabidopsis made the cotyledon insensitive to ABA. Furthermore, transgenic plants also exhibited salt and drought stress tolerance. The results of RT-PCR for RD29B gene located down-stream implied that OsAP21 over-expressed plants had a high expression level of RD29B gene compared to the WT plants, and drought and salt treatments could enlarge these differences.It is reasonable to presume that OsAP21 participates in ABA-dependent signaling transducation pathway and can enhance ABA content during drought and salt stress. ABA activated related protein kinase that assisted OsAP21 transcription factor binding to ABRE cis-element in promoter of dowmstream genes and up-regulated expression. Finally, it resulted in tolerances for transgenic Arabidopsis based on research results. But more work need to do to elucidate the mechanism of OsAP21 in drought and salt tolerances in plant.