The Molecular And Cytological Analysis Of WHIRLY2 Functions In Arabidopsis During Growth And Senescence

WHIRLY2 protein is one of plant-specfic transcription factor, which can bind to single-strand DNA (ssDNA). Over-expression WHIRLY2 protein in Arabidopsis leaves reduces mitochondrial DNA content, and shows abnormal distortion. On the other hand, over-expression WHIRLY2 protein in Arabidopsis pollen cell can improve mitochondrial DNA stability and thus influence pollen development. These results demonstrate that WHIRLY2 protein plays different functions in diverse tissues. In order to systematically investigate the functions of WHIRLY2, we observed the phenotype of WHIRLY2 transgenic Arabidopsis plants and analyzed the expression difference of downstream genes in this research. We aslo evaluate the WHIRLY2 functions in the hormone related pathways by various phytohormone treatment experiments.This research contains two parts. In the first part, we observed the phenotype of WHIRLY2 transgenic Arabidopsis plants, identified some downstream genes of WHIRLY2 and also analyzed the influence of different kind of phytohormone on WHIRLY2 transgenic plants. In the second part, we analyzed the influence of different levels of WHIRLY2 protein on silique development and its role in mitochondria genome transcription.The results were displayed as follows:1. We studied the functions of WHIRLY2 on plant senescence. It was showed an enhanced senescence phenotype in the overexpressing WHIRLY2 line (35S::Why2-YFP) and a delayed senescence phenotype in the knockout WHIRLY2 line (KO:Why2-1) were observed. Senescence-associated marker gene SAG12 and dark-induced senescence related gene WRKY22 were showed upregulated expression in 35S::Why2-YFP line. By contrast, MYB113, a membwe of the MYB transcription factor family, was showed downregulated expression. At the same time, MYB113, ARR2, ERD and At2g43620 were showed upregulated expression in the KO:Why2-1 line.2. We made a study on the relationship between WHIRLY2 and jasmonic acid (JA) synthesis pathway. JAS1 and TAT3 were upregulated in KO:Why2-1 line. MeJA-treatment showed obvious senescence phenotype in 35S::WTiy2-YFP line compared to the wild-type Arabidopsis, and the gene encoding Jasmonic acid carboxyl methyl transferase (JMT) showed high transcriptional level. In contrast,35S::Why2-YFP seedlings showed less sensitive to MeJA treatment compared to the other lines. These results suggested that WHIRLY2 can regulate plant development via inducing the expression of some genes of JA related pathway.3. We verified the relation between WHIRLY2 and the stability of mitochondrial genome. Root length in 35S::Why2-YFP line was not suppressed in Ciprofloxacin (CIP) medium. This result confirmed that WHIRLY2 functions on maintaining the stability of mitochondrial genome.4. We observed the phenotype of 35S::Why2-YFP and KO:Why2-1 lines after the treatment with various phytohormones.35S::Why2-YFP line showed more sensitive phenotype after ABA-treatment; In MeSA treatment, the results were opposite to MeJA-treatment; 35S::Why2-YFP line showed less sensitive phenotype compare to wild-type; Different transgenic Arabidopsis lines showed the same phenotype after KT-treatment. These results suggested that WHIRLY2 can balance different hormone signals to regulate Arabidopsis development.5. We observed the influence of WHIRLY2 on silique development. WHIRLY2 can bind to telomeric repeat sequence and regulate the expression levels of mitochondrial energy metabolism related genes, as a result of maintaining the stability of mitochondrial genome.