| Summary: | 博士 === 國立中興大學 === 生物科技學研究所 === 101 === In higher plants, recent studies revealed that the operation of the long-distance communication network is mediated by the phloem translocation system. The environmental inputs, which include biotic stresses such as pathogen or insect attack, and abiotic stimuli, are mainly received by mature leaves. These inputs are converted into mobile signals and transported to the apices to orchestrate the proper developmental programs. Analyses of the phloem sap compositions and the grafting experiments demonstrate that endogenous mRNAs, small RNAs, proteins and phytohormones move long-distantly to regulate flowering, leaf architecture, tuberization, pathogen defense, and many other developmental processes. Although the movement of phloem mobile RNAs appears to be mediated by non-cell
autonomous RNA-binding proteins, whether these mobile RNAs contain the information motifs necessary for long-distance trafficking is still to be investigated. In the first chapter, we aimed to identify the RNA mobile motifs that are important for movement. Using linker-scanning analysis, we demonstrate that the specific RNA structural motifs on Arabidopsis GA-INSENSITIVE (GAI) RNA play a role in mediating GAI RNA movement. In the second chapter, we intended to investigate the molecular nature of the antiflorigen. In 1970s, the concept of photoperiodic dependent and graft-transmissible florigen and antiflorigen has been proposed based on the results of classical grafting experiments in tobacco plants. Recently, both RNA and protein of FLOWERING LOCUS T (FT) are the florigens whereas the identity of antiflorigen is still unclear. In this chapter, we showed that the Arabidopsis thaliana
CENTRORADIALIS homologue (ATC) RNA, a member of FT family, is a systemic floral inhibitor in Arabidopsis. We found that ATC antagonizes FT activity to regulate flowering. In addition, we also showed that the CENTRORADIALIS-like (CET), an ATC homolog in tobacco, may contribute to the antiflorigen activity. These results suggest that the florigen and antiflorigen are evolved from the same ancestor, but function antagonistically to fine-tune floral initiation in plants.
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