Functional Analysis Of MYB Family Transcription Factors OsMYB2 In Rice (Oryza Sativa L)

Regulation of gene expression at the level of transcription controls many crucial biological processes including growth and development, stress response, signal transduction and disease resistance. A number of different factors are required for the processes of transcription, in which the transcription factors play an important role. The MYB transcription factors comprise one of the largest families in plant transcription factors. It can specifically interact with MYB cis-acting elements and induce expression of multiple drought- or cold-responsive genes. Constitutive overexpression of MYB genes has been reported to trigger the MYB regulons and enhance freezing, drought, and salt tolerance in some of the transgenic plants. In this article, we analyzed the function of OsMYB2, a MYB transcription factor in rice.Sequence analysis reveals that OsMYB2 contains two imperfect tryptophan repeats (R2 and R3) in the N-terminal conserved region, which is characteristic of most plant MYB transcription factors. Furthermore, secondary structure analysis of OsMYB2 predicts that the tryptophan repeats form helix-turn-helix DNA-binding motifs. It also contains a potential ATP-GTP-binding site, and a nuclear localization.Real-time RT-PCR analyses were performed to determine the expression profiles of OsMYB2. In three-week-old seedlings, expression of OsMYB2 was induced by dehydration ( PEG), high salt ( 200mM NaCl ), and ABA(200μM), but not by cold (4oC). In addition, we examined tissue-specific expression of OsMYB2 in rice using real-time RT-PCR. The OsMYB2 transcripts were detected in all organs tested including root, stem, leaf and spike, but the highest level was in root.Since OsMYB2 is a transcription factor, it might be modulating the expression of genes involved in these processes. To test this hypothesis, gene expression analysis of possible regulated genes in transgenic plants was carried out by real-time RT-PCR. Under ABA or high salt treatment, RD29A and RD22 were down-regulated, whereas ADH was up-regulated.Transgenic Arabidopsis thaliana, Columbia plants overexpressing OsMYB2 were also obtained to further investigate the precise function of OsMYB2. In contrast to non-transgenic plants, these transgenic lines showed hypersensitive to ABA. Overexpression of OsMYB2 decreases tolerance to drought, salt and heavy metal, but increases tolerance to suger.Since MYB transcription factors have been determined to interact specifically with MYB cis-element, the DNA-binding specificity of OsMYB2 was examined by using yeast-one-hybrid assay. The TAACTG cis-element from the enhancer of SV40 was used to construct bait plasmid. The experimental results indicated that OsMYB2 specifically bound to TAACTG. On averageβ-galactosidase activity was decreased 2-fold relative to the control for the MYB cis element. It suggested that OsMYB2 was likely to be a transcriptional repressor and played function of negative regulation in gene expression.