| Summary: | 碩士 === 國立中興大學 === 生物科技學研究所 === 99 === The mammalian target of rapamycin (mTOR) interacts with the regulatory-associated protein of TOR (RAPTOR) to activate p70 ribosomal S6 kinase (p70s6k), and further activates its downstream - the 40S ribosomal protein S6 (rpS6), resulting in an increase of translation for 5’TOP mRNAs. 5’TOP mRNAs are specific mRNAs including an oligopyrimidine tract (CU rich) in 5’-UTR. The mTOR signaling pathway plays an important role in regulating cell growth and development. However, its function remains unclear in plants. In Arabidopsis thaliana, AtPK6, AtPK19 and AtS61, AtS62 are homologues to p70s6k and rpS6, respectively. To perform functional studies, AtS61 and AtS62 were cloned and characterized. Ectopic expression of RNAi and antisense of AtS61 or AtS62 inhibited the cell expansion and significantly reduced the plant size and root length. Moreover, the prohibition of the shoot apical meristem (SAM) development and the influence on survival were observed in some transgenic plants. On the other hand, ectopically expressing AtS61 or AtS62 in Arabidopsis caused male sterility. By Alexander’s staining, pollen of transgenic lines were normal and active, thus the male sterility was caused by the delayed anther dehiscence and pollen release. Normally, treatment of Arabidopsis with ethylene (ET) or jasmonic acid (JA) will promote anther dehiscence. However, the anther in transgenic lines did not dehiscent after ethylene or jasmonic acid treatment. The transgenic lines showed reduced expression levels of genes involved in ethylene signaling pathway. These data suggest that AtS61 and AtS62 were involved in ethylene and jasmonic acid signaling pathway to regulate anther dehiscence. To investigate 5’TOP mRNAs regulated by AtS61/AtS62, the 5’-UTR of candidate genes such as WUSCHEL (WUS), BONZAI1 (BON1), PROMOTION OF CELLSURVIVAL 1 (PCS1), BRASSINAZOLE-RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) were analyzed and oligopyrimidine tracts in the 5’-UTR were identified. We found that the mutants of these genes encoded putative 5’TOP mRNAs caused the similar phenotype as the mutant lines of AtS61 and AtS62. By transient transfection of tobacco, we found that the translation levels of these 5’TOP mRNAs were affected by AtS61 and AtS62. Further characterization and analysis of the mechanisms regulated by AtS61/AtS62 and the candidates of 5’TOP mRNAs are in progress.
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