| A large scale random sequencing was performed for a cDNA library prepared from developing rice endosperms of 10 -d-old immature rice seeds. 14 496 clones had been sequenced and generated 9 215 sequences with 3'- Poly(A)+-ends. It was shown that the 9 215 3'-EST could represent 2959 unique genes after analysis with various bioinformatics tools. Among them, 471 (16% )could represent known-genes, 446 (15%) genes had a putative function ( similar to ) , 624(2 l%)genes had EST matches in http://www.ncbi.nlm.nih.gov/dbEST/rice database, another 1218 (41 %) are novel genes that had no mathch in dbEST.The expression abundance of the 2959 uni-genes were different in developing rice endosperm. In this sequencing experiment, 2490 genes(84.2%) had been sequenced not more than 2 times, we classified these genes as low expression abundance genes. 389 genes (13.2%)had been sequence more than 2 times but less than 8 times, we regard these genes as moderate expression abundance genes. There were only 80 genes (2.6 %) that had been sequenced more than 7 times, that constituted only a considerably small percentage of the total 2959 uni-genes, we classified these genes as high exression abundance genes. However, totally, these 80 highly expressed genes had been sequenced 4673 times, that is 50.8% of the total sequences we had got. On the other hand, the 3'-EST of the low expressed 2490 genes only accounted for 31.8 % of the total 3'-EST. And the 389 moderately expressed genes account for 17.5 % of the total EST. Among the 80 genes with high expression abundance, 47 genes were function-annotated .There was significant redundancy in the genes encoding storage proteins in developing rice endosperm. The number of EST for gluteline, prolamine and globulin were 2597, 614 and 105 , repectively, and they accounted for 36 % of the total 9215 EST . The amount of EST encoding proteins involved in protein biosynthesis mechanism were large ,too. There were 617 EST of ribosomal proteins and ribosomal RNAs genes, that account for 6.7% of the total EST. EST of other genes encoding proteins involved in the process of translation accounted for 0.6% of the total EST. The large number of EST of genes encoding ribosomal proteins,ribosomal RNAs, and proteins involved in translation mechanism indicated that protein synthesis was the main cell process in rice endosperm. Scores of genes that encoding proteins involved in protein folding, protein degradation and amino acid metabolisms were also identified in this experiment. 11 molecular chaperone-encoding genes were identified , which included 5 heat shock proteins , Among them, Heat shock protein 70 , protein disulfide isomerase and cyclophilin-2 were expressed with high abundance. We also identified 27 genes encoding protein involved in protein degrading processes, including 16 ubiquitin protein genes , 7 proteinase genes and 4 20s proteasome proteins genes. Totally, 11 genes encoding enzymes involved in amino acids metabolisms were identified, in which S-adenosyl methionine synthetase-1 and S-adenosyl methionine synthetase-2 and aspartate aminotransferase were highly expressed in endosperm.The genes that encoding proteins involved in starch biosynthesis were sequenced 159 times altogether, accounted for 1.7 percentage of the total EST. 18 genes encoding enzymes involved in starch metabolism were identified. ADPG -pyrophosphorylase, soluble starch synthase, branching enzyme, starch debranching enzyme, Waxy gene for starch synthase are the enzymes that directly take part in starch synthesis. The sequencing results show that the corresponding genes were all highly expressed in developing rice endosperm, indicating there existing intensive biochemical reactions of starch synthesis in amyloplasts.As expected, we had only identified 2 genes encoding enzymes directly involved in fatty acid biosynthesis, they were stearyl-ACP desaturase and acyl carrier protein II gene, and their expression abundance were low, suggesting there was little fatty acid synthesized in rice endosperm tissue. However, b... |
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