Study On The Function Of Rice OsCATA Gene In Photorespiration

In the long process of evolution, plants have formed the photorespiration pathway to adapt the environment. Although photorespiration reduces the efficiency of the Calvin cycle, photorespiration is an essential part of all photosynthetic organisms. Especially under CO2-limited conditions, photorespiration provides a substrate for the Calvin cycle. Photorespiration is an important and protective mechanism which can eliminate redundant ATP and NADPH in the photosynthetic electron transport chain and keep an imbalance between the amount of the light energy absorbed and the capacity of the plant for its utilization to avoid photoinhibition. H2O2 produced by photorespiration pathway in peroxisomal has a dual effect in plants.It can be used as a redox cell signal. However, H2O2 also has toxicity and will trigger programmed cell death. In this study we used OsCATAi transgenic rice to analyse the function of OsCATA in photorespiration. By changing the ratio of CO2 and O2, we were able to analyze the relations among photorespiration, photosynthesis, photosystem and antioxidant system. Besides, the yeast two-hybrid system was also used to screen a two-week-old rice leaves’cDNA library to detect hybrid proteins which could interact with CATA. The major results are as follows:1. Transgenic plants were identified and analysed by quantitative PCR, Western blot and CAT activity. Compared with Oryza Saliva, the expression degrees of two lines OsCATAi decreased to 28% and 15% according to the results of quantitative PCR. The protein content of OsCATA is difficult to be detectd by Western blot. CAT activity is also decreased to 7% and 6%. At the same time, the expression degrees of OsCATC have increased to 7.50 times and 8.16 times. H2O2 histochemical tests showed that H2O2 content increased in the OsCATAi transgenic rice.2. The digital gene expression of OsCATAi transgenic rice and Oryza Sativa in CO2 and O2 treatment shows that, compared with Oryza Sativa in air, there are 1303 genes up-regulated and 391 genes down-regulated in OsCATAi transgenic rice. The upregulated and downregulated genes in CO2 and O2 treatment are:1053:532(high CO2 treatment),282:397(low O2 treatment) and 445:564(high O2 treatment). Compared with normal air, the upregulated and downregulated genes in Oryza Sativa under CO2 and O2 treatment is:451:491 (high CO2 treatment),282:397(low O2 treatment) and 445:564 (high O2 treatment).3. Compared with normal air, the performances of Oryza Sativa under high CO2 and low O2 treatment are similar:Rubisco initial activity and total activity, GLO activity, net photosynthetic rate and gross photosynthetic rate were all declined. The expression of genes in C3 and C2 pathway OsFBA、OsRPK、OsRPI、OsrbcL、OsHPR and OsGDC were also descreased, same as chlorophyll fluorescence parameters qP and Yield.The activity of SOD and APX increased, but the activity of GPX, CAT, GR and GST went down. The content of GSH and GSSG were also decreased. Once under the treatment of high O2, all these changes of Oryza Sativa on physiological and molecular were little, but higher than high CO2 treatment.4. Rubisco initial activity and total activity, GLO activity, net photosynthetic rate and gross photosynthetic rate, chlorophyll fluorescence parameters qP and Yield were all declined under different trearments in OsCATAi transgenic rice compared with Oryza Sativa. The expression of genes in C3 and C2 pathway were descreased also. The activity of antioxidant enzyme and content of antioxidants increased. The performance under high O2 treatment is higher than high CO2 and low O2 treatment, but the changes are not significant.5. The yeast expression vector bait pGBKT7-CATA was constructed and confirmed to be no ill behaver and self activation in yeast cell. Two-week-old rice leaves’ cDNA library was screened afterwards and thirteen protins were found during initial screening processes.