| Plant ripening is a developmentally controlled process that is regulated by plant hormones. Ethylene, a colorless gas hormone emitted by almost all parts of higher plants, has been well recognized to play a critical role particularly in the control of climacteric fruit ripening. In the category of climacteric fruits, banana is a typical one of which the ripening process shows a characteristic burst in respiratory rate in response to a sharp peak in ethylene production just before the ripening phase. Therefore', the climacteric ripening of banana is under control of the production of ethylene as well as the ability of the fruit to perceive ethylene. A long-term primary objective of pre- and post-harvest management of banana ripening for a prolonged storage life therefore has been focused on manipulation of the response of banana to ethylene. These include efforts in three major aspects, inhibition of ethylene biosynthesis, removal of ethylene from storage environment, or suppression of the sensitivity of banana to ethylene exposure.Ethylene responses of climacteric fruits at molecular level are composed of three sequentially relayed steps: ethylene perception at cellular membrane, intracellular ethylene signal transduction, and changes of expression of ethylene-responsive target genes. The last is major a nuclear event involving ethylene-induced transcriptional activation/repression of the target genes via ethylene responsive elements (EREs) located at genes' promoter regions. Delineation of the mechanisms associated with these processes will eventually lead to development of strategies for a fine-tuned control of climacteric ripening fruits as banana.Our previous studies have isolated a putative ethylene receptor gene from climacteric ripening banana fruit. Further functional characterization of the gene identified, however,is hampered technically due to lack of an operative transformation system in bananas. The current investigations were aimed to utilize alternative approaches to address this issue, while RNA interference (RNAi) was applied because of its merits recognized in compelling data for specific, efficient, fast, and cost-economic generation of functional information of candidate genes from almost any origin. In principle, RNAi is a concept comprised of post-transcriptional gene silencing (PTGS) mechanism. The phenomena of PTGS was initially found in transplants where expression of transgenes were frequently silenced/lost, indicating existence of a defense mechanism in the host to squelch the intruding heterologeous genetic information.Mechanistically, gene-silencing is induced through formation of long sequence-specific double-stranded RNAs (dsRNAs; typical >200 nt), which upon subsequently entering a so-called RNA interference pathway get processed into 20-25 nucleotides by an RNase Ill-like enzyme (Dicer enzyme). The derived small RNAs(referred as small interference RNA, siRNA) assemble into endoribonuclease-containingcomplex RISC (RNA-induced silencing complexes). The RISC is then guided by siRNAsto cognate RNA of a specific target gene via complementation formed between the siRNA and the target RNA. This results in the elimination (silencing) of the target gene expression by RISC-mediated cleavage and degradation of the target gene transcript. Based on these studies, theoretically, silencing of any gene of interest is accessible by introduction of dsRNA duplex specific to the target gene sequence. In fact, targeted knock-down of genes in variety of organisms and cell types (e.g., worms, fruit flyies, plants, mammalian cells and model animals) has provided significant insights into the functions of numerous genes. With genome-wide sequencing projects being finished in human and several other species in contrast to their largely unknown cognate functions, the importance of RNAi-based applications will not be underestimated at this post-genome era.We have chosen Arabidopsis thaliana as experimental materials in order to establish arefined RNAi system for future studies of ethyle...
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