| Summary: | 碩士 === 國立嘉義大學 === 農藝學系研究所 === 103 === Protein phosphatase 2A (PP2A) has been implicated in growth, development, hormone signaling, and stress tolerance in plant cells. Stress signal transduction pathways start with signal perception, followed by the activation of protein phosphorylation cascades involving protein kinases and phosphatases, and finally target proteins involved in cellular protection or transcription factors controlling sets of stress-regulated genes. This study aimed to understand the possible role of PP2A catalytic subunit isoform 2 (OsPP2Ac-2) on abiotic stress tolerance in rice. A previously selected T-DNA insertional mutant M5149 has been analyzed to contain multiple T-DNA insertions in which one of the insertions tagged at OsPP2Ac-2 gene. To isolate a single insertional line, M5149 was backcrossed with Tainung 67 and their progenies were further analyzed. The BC1F2-7-1 line was selected from the segregation population. This is a single insertional mutant which tagged at OsPP2Ac-2 gene identified by genotyping analysis, GUS staining and Southern blot analysis. We constructed the OsPP2Ac-2 gene overexpression plasmid drived by ubiquitin promoter. Totally 32 transgenic cell lines and 14 T0 transformants from 4 times of transformation operation. The results showed that OsPP2Ac-2 gene expression was inhibited under sorbitol treatment at seedling stage. Overexpressed transgenic lines showed more tolerant to osmotic stress treatment but BC1F2-7-1 knockdown mutant line was sensitive as compared with TNG67 at seedling stage. The chlorophyll fluoresence value (Fv/Fm) consistent with the phenotypic observation. On the other hand, the cell amplification efficiency of transgenic cell lines are similar to TNG67 either grown on culture medium with or without sorbitol treatment. But their growth rate were significantly decreased under early sorbitol treatment which may lead to hypersensitive to osmotic stress. Besides, the NBT staining was stronger and DAB staining was lighter in OxOsPP2Ac-2 overexpression cell lines than in TNG67 under sorbitol treatment for 20 days which may derive from higher level of superoxide and low level of hydrogen peroxide accumulation. We concluded that OsPP2Ac-2 gene may act as a negative regulator in rice by affecting downstream cell growth genes and stress responsive genes.
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