Functional Investigation Of CYCLIN-DEPEDENT KINASE G2in Arabidopsis

Plant growth and development depend on the programed cell division, expansion and differentiation processes, and the cell division, especially the mitosis, as well as its regulatory mechanism, are essential for plant morphogenesis and developmental transition. Consequently, the regulation of cell cycle is important for plant development. Cyclin-dependent kinases (CDKs) are serine/threonine protein kinases whose activity relies on binding and activation with partner cyclins. These cyclin-CDK heterodimeric complexes can phosphorylate diversified substrates, and thus control transcription and cell-cycle.In this dissertation, we found that, the CDKG2(CYCLIN-DEPEDENT KINASE G2), a member of Arabidopsis CDKs, is negatively involved in plant flowering transition, and further research revealed the potential mechanism of CDKG2in plant flowering control. The detailed experiments and results are described below.In this study, two independent functional null mutants of CDKG2(cdkg2-1and cdkg2-2) were employed to study the physiological roles CDKG2. The cdkg2-1and cdkg2-2were both with decrement of vegetative growth and early flowering phenotypes either in long-or short-day light conditions. The mutant early flower phenotype could be reversed by cdkg2/CDKG2functional complementation. In addition, the overexpression plant lines (OE-1and OE-2) of CDKG2delayed flowering time than wild type. To further analyze the mechanism of CDKG2in regulation of plant flowering transition, the known pathways controlling flowering transition were investigated. Further phenotypic analyses, including short/long day treatments, vernalization and GA treatments, together with quantitative Reverse-Transcription PCR data for gene transcripts governing plant flowering transition, suggested that CDKG2is involved in autonomous pathway.The expression profile of CDKG2detected by promoter-GUS strategy revealed that, this gene is ubiquitously expressed during all the plant developmental stages, including seed, seedling and grown plant, especially with very high expression level in meristems. Together with the evidence that CDKG2is subcellularly located in nucleus, suggest that CDKG2may act with other interaction cyclins in nucleus to regulate the gene expression and negatively be involved in plant flowering transition.Beside of plant flowering, the CDKG2was also found to be involved in salt inhibition of seed germination process, and cdkg2-1and cdkg2-2germinated earlier with higher germination rate than wild type (Col-0). Suggesting CDKG2is also a essential element of plant in response to salt stress during seed germination.