Study Of Apple ACC Synthase Gene MdACS6and Its Regulatory Role In Fruit Ethylene Biosynthesis

Apple is one of the fruit with largest cultivation area and yield in the world. Fruit shelf-life determines the economic value of mature apple fruit, which is regulated by ethylene, a major plant growth regulater and ripening hormone. The precurse of ethylene ACC is formed from SAM under the catalyzation of ACC synthase and converted to ethylene by the oxidation of ACC oxidase (ACO). The formation of ACC is generally considered to be the rate-limiting step in the biosynthesis of ethylene. Thus, ACS is the most important enzyme in this pathway. The biosynthesis of ethylene has been divided into two systems in higher plants; and different system is regularted by different ACSgenes. In this paper, we explored all ACS genes in the apple genome, and found unreported ACS gene, which was named MdACS6. We claried its sequence and study the functiom in apple fruit during development and shelf-life by Agrobacterium infiltration. The results will be greatly helpful in clarifying the role of MdACS6in regulating apple fruit ripening and in integrating the research on fruit ripening, as well as in supporting the technology of fruit storage. The results are as follows;1. A total of19ACS genes were revealed in apple genome by exploring the genome sequence data. It is the largest ACS gene family currently known in plant. Six of these ACS genes were expressed in apple fruit, among which four of them were new members of this gene family. One of them named MdACS6was found to be expressed higher during fruit development and storage.2. MdACS6gene was cloned in this study. The3’-untranslated region (UTR) was obtained by3’-RACE. Sequencing analysis showed that the cDNA of MdAC6is1,906bp in length, and includes247bp of5’-UTR,138bp of3’-UTR and1,521bp of open reading frame (ORF). The ORF encoded a predicted polypeptide containing507amino acid residues. The coding region of MdACS6was compared to its genomic DNA and revealed4exons and three introns.3. The ordinal expression patterns of MdACS6, MdACS3a and MdACS1, together with their responses to1-MCP treatment, indicated that MdACS6regulates in System1, MdACS1in System2and MdACS3a in the transition from Systeml-to System2-ethylene biosynthesis.4. To further study the function of MdACS6, we overexpressed it in apple fruit by Agrobacterium infiltration. We found Systeml-MdACS6regulates the action of MdACS3a possibly by interacting with MdMADS17and/or MdMADS19, and then regulates the System2-ethylene biosynthesis. We deeply discussion the reason of this phenomenon.Taken together, MdACS6operates in System1ethylene biosynthesis and regulates the expression of MdACS3a and further affects System2ethylene production.