Isolation And Characterization Of Stress-Related MYB Genes And Stress-Inducible Promoters

Abiotic stresses are major limiting factors for plant productivity, and with global environmental degradation and abnormal climate changes, they will increasingly endanger food security. So, it is important for us to know how plants sense and adapt to the adverse environmental conditions and which genes act with crucial roles during the stress sensing and adaptation processes. A number of studies suggest that stress resistance can be significantly improved by engineering such important genes.This study is comprised of two parts. The first part is isolation and characterization of stress resistance candidate genes. Fourteen stress-responsive MYB genes were overexpressed in rice to test their effectiveness on improving stress resistance. CST1 (Cold and salt tolerance 1, OsMYB30) was found to be one of the MYB genes involved in cold and salt tolerance. The second part is isolation and characterization of stress-inducible promoters, and a drought-inducible promoter named Oshox24P was identified. The main results are as follows:1. The over-expression vectors of 14 candidate genes were constructed and introduced into japonica rice Zhonghua 11 by Agorobacterium-mediated transformation.2. After stress testing at seeding stage, transgenic rice of two candidate genes showed increased or deceased stress tolerance. One of the candidate genes, CST1, was chosen for further analyses.3. Bioinformatics analysis showed that CST1 belongs to R2R3-MYB. The phylogenetic tree based on the MYB-binding domain revealed that CST1 is close to MYB 15 from Arabidopsis and OsMYB4 from rice.4. The CST1 transcript was detected in most organs and tissues of rice, but the highest level was in lemma and palea, secondary branches, and anthers, and the lowest was in panicle. The expression level of CST1 was increased during cold stress but decreased during salt stress. 5. T-DNA insertion mutant cstl showed significantly increased cold and salt tolerance compared to the wild type plants.6. A number of cold-related genes were detected by Real-time PCR concluding DREB/CBF genes and other genes reported, however, the expression of these genes had no significant different between the overexpression and mutant plants. So, it is suggest that these genes weren’t regulated by CST1 during cold stress.7. Based on DNA chip analysis, large member of genes changed their expression on transcriptional level; this result indicated that CST1 act as an important role in cold stress tolerance.8. Promoter::GUS fusion constructs for 12 stress-inducible promoters were made and introduced into japonica rice Zhonghua 11.9. GUS activities of transgenic plants of 5 candidate promoters were analyzed under different stresses. Promoter Oshox24P was found to be strongly induced under drought condition, while the others were induced slightly.