| Summary: | 碩士 === 國立中興大學 === 生物科技學研究所 === 103 === In Arabidopsis, GIGANTE (GI) is known as an important flowering time regulatory gene, which is regulated by circadian clock. Mutation in GI caused the delay of the flowering time and the increase of the tolerance to oxidative stress in Arabidopsis. GI has been reported to interact with FLAVIN-BINDING, KELCH REPEAT, F-BOX 1(FKF1) to regulate downstream genes such as CONSTANS (CO) in flowering pathway. We have cloned GI orthologue PcGI from non-flowering ferns Cretan Brake. The expression of PcGI also showed a circadian rhythm. Furthermore, transient expression of AtGI, PcGI, PcAt-GI which contained the C-terminus of AtGI and N-terminus of PcGI, and AtPc-GI which contained the C-terminus of PcGI and N-terminus of AtGI were performed in tobacco cells. The results indicated that the localization of AtGI was detected only in nucleus, which had the speckled nucleus. The PcGI was detected in nucleus as well as in peroxisome. The localization of PcAt-GI in peroxisome and nucleus was stronger than that for AtPc-GI. These results revealed that the C-terminus of the AtGI is functionally more important than N-terminus in nucleus localization and flowering. The N-terminal portion of PcGI is the major motif for PcGI to localize in peroxisome and is associated with senescence and oxidative stress. PcGI was detected in peroxisome in red and weak light, but not in blue light. The AtGI and PcGI were changing from speckled to disperse in nucleus by interacting with FKF1 in blue light but with less effect in red and weak light. PcGI competed and prevented the entering of catalase 3 (CAT3) into peroxisome and resulted in the hydrogen peroxide accumulation. Our result implied that PcGI played a major role in regulating oxidative stress and antibiotic tolerance in ferns whereas GI orthologues become more important in regulating flowering time in flowering plants during evolution.
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