The Characterization On Cytokinin Two-component Signalling System In Rice (Oryza Sativa L.)

To indentify cytokinin (CTK) signaling components in rice, a sequence similarity based alignment method is used. Five cytokinin receptors (OsHK1-4 and OsHKL1 ) . 5 His-containing phosphotransfer proteins (OsHP1-5) and 19 response regulators (OsRR1-19) were identified in the rice genome. The bioinformatics analysis of the TCS (two-component signal) components were conducted. The expression pattern of CTK signaling components in the transgenic plants with RNAi of CTK recaptors and the the cytokinin insensitivity mutants were investigated. The results were as following:1. Among 5 OsHK genes, 5 OsHP genes and 19 OsRR genes, the transmitter domain and receive domain were absent in OsHKL1 and no His residues were found in the OsHP3, OsHP4 and OsHP5. The key DDK residues were not integrated in OsRR 11, OsRR 12 and OsRR 13. The conserved domains were observed in the other TCS genes. The conservation at the amino acid level is highly homologous among the TCS genes among rice, Arabidopsis and maize. Based on the phylogenetic analysis, the closed relationship was found between the TCS genes of rice and maize compared with the relationship between rice and Arabidopsis.2. The TCS genes are distributed over twelve rice chromosomes. The OsRR1 and OsRR2, OsRR3 and OsRR5, OsRRI5 and OsRR19 are duplicate pairs. They are one clustering. respectively, on the phylogenetic tree, which suggests that an evolutionary relationship is reinforced by the duplication of these genes on the genome.3. The transcripts of OsHK1, 0sHK2, OsHK3 and OsHK4 were induced by exogenous cytokinin as 6-BA treatment in roots but not in the leaves. Transcripts of type-A OsRRs were rapidly accumulated after cytokinin treatment. While the type-B OsRRs were not up-regulated by 6-BA in roots and the leaves. The majority of the His-Asp phosphorelay signaling factors were expressed at various levels in roots, leaves, stems, flowers and ears, but the expression patterns differed.4. The OsHK1, 0sHK2, 0sHK3 and 0sHK4 can complement the function of the yeast SLN in a cytokinin-dependent manner and they functioned as cytokinin-responsive histidine kinases. The OsHK like gene (OsHKLl) did not response to cytokinin. The transcript levels of most His-Asp phosphorelay signaling factors are changed in the transgenic rice plants with RNAi of cytokinin receptors and the changes are different between roots and leaves. The results were as following: The OsHKl regulate the expression of OsHP 1, OsRR14 and OsRR8 in roots and OsHP4, OsRRl 7, OsRR2 and OsRR4 in leaves. The...