| Summary: | 博士 === 國立中央大學 === 生命科學研究所 === 99 === Abstract
The DEAD-box protein families are involved in RNA metabolism, including pre-mRNA splicing, ribosome biogenesis, RNA decay, and gene expression. This study indentifies a homolog of the RH36 gene encoding a DEAD-box protein in Arabidopsis, AtRH36, and rice, OsRH36. The genes were expressed ubiquitously throughout the plant. The AtRH36-GFP and OsRH36-GFP fusion protein were localized in the nucleus and nucleolus. rh36 homozygote mutants, atrh36 and osrh36, were lethal. The progenies of selfed heterozygote lines were obtained at a ratio of 1:1, as heterozygote to wild type, suggesting that the RH36 gene was involved in the gametophyte development. A reciprocal cross was therefore conducted to determine that the function of AtRH36 is via the female gametophyte. The progress of female gametogenesis was retarded in atrh36-1, and asynchronous development of female gametophyte within the same pistil was found. Knockdown of AtRH36 presented a pleiotropic phenotype and led to accumulation of unprocessed 18S pre-rRNA. In phylogenetic analysis, AtRH36 and OsRH36 were homologous to yeast DBP8p. Furthermore, functional complementation tests among three homologous DEAD-box protein genes indicated that OsRH36 can restore segregation distortion in the Arabidopsis atrh36-1 mutant, but cannot complement the lethal phenotype in the yeast dbp8p mutant. Therefore, we suggest that OsRH36 is required for rRNA biogenesis and megagametogenesis in rice, consistent with the function of AtRH36 in Arabidopsis. These results suggest that RH36 is essential for the mitotic division cycles during development of female gametogenesis and plays an important role in rRNA biogenesis in rice and Arabidopsis.
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