Expression Profiling Of Chloroplast-encoded Proteins In Rice Leaves At Different Growth Stages

Background: Chloroplast is the critical organelle for transforming light energy into chemical energy in plant. Besides photosynthesis, chloroplast also takes part in the other important biological processes, such as metabolism of fatty acids and the pigment synthesis, amino acids and secondary metabolism. Chloroplast is a semiautonomous organelle, including a complete genetic system used in self-replication. At present the whole genome sequences of chloroplast of many plants have been released and the knowledge about biological processes in chloroplast has been accumulated. However, limited information regarding the expression of chloroplast-encoded proteins is available.Aim: The generation of specific antibodies against rice chloroplast-encoded proteins to investigate the expression profiling of rice chloroplast-encoded proteins in different stages of rice leaves and accumnulate basic information for functional studies.Materials and methods: Epitopes were predicted for candidate gene-encoded proteins and syntheticed high peak value peptides. Polyclonal antibodies were generated by rabbit immunization. Western blotting analysis were carried out for rice material collected at different developmental stages, including seeding stage 1cm, 2cm, 5cm, 10cm, 15cm, tilling stage, booting stage, flowering stage, filling stage. Comparison analysis with transcriptional information was carried with rice MPSS datebase in seeding stage and tilling stage.Results: In this experiment, 15 chloroplast genes were selected from chloroplast-encoded proteins and the expression profiling in different stages of rice leaves were investigated by Western blotting. The results indicated that the expression patterns of 7 photosynthesis-related proteins are similar and the expression level increase steadily as leaves grow taller. Until the booting and flowering stages, the expression reached the highest-level, and then decreased at filling stage. The correlation between the expression of photosynthesis-related proteins and the photosynthesis was observed. The expression levels of 4 RNA polymerase related to DNA replication were at their highest-level at seedling stage, which indicated that they perform their functions during the early stage. However, 4 NADH dehydrogenases exhibited two kinds of expression patterns. Subunit-2 and -4 reached their highest-level when the leaves were 1cm in length during seedling stage. While, subunit-5 and -7 reached theirs in middle and later stage of seedling. The results implied their different functions during seedling stages. Compared with transcriptional information in the two stages, it higher level transcriptional signal in seeding stage than tilling stage which in parallel with protein expression.Conclusions: By the expression profiling of 15 chloroplast-encoded proteins in different stages of rice leaves, we found that the proteins have three expression patterns. This experiment results revealed the in rice leaves at different growth stages and the correlation between the proteins and the growing process in a direct and relative quantitative way, and the diversification of protein expression of chloroplast-encoded proteins provided significant information for further research of their function. It also provided important scientific basis for chloroplast function in vital processes such as rice normal growth and response of adversity.