Isolation And Expression Of α-farnesene Synthase Gene Of The Peel Tissue Of Yali Pear (Pyrus Bretschneideri Rehd)

Superficial scald, a physiological storage disorder of apples and pears, can reduce edible quality (especially appearance quality), market value, and the resistance to disease; hence lead substantial loss in economy. But up to now the root cause of scald is not clear, and the use of DPA and Ethoxyquin, which have been used commercially to control scald, has raised concerns of food safety and environmental problems in the world. The studies on mechanism of scald development and high effective non-chemical measures are a popular field in postharvest physiology.α-Farnesene has been proven to be correlated to the development of superficial scald.The accumulation ofα-farnesene in the skin of apple fruit during storage appears to be predominantly through classical mevalonate (MVA) pathway. 3-Hydroxy-3-methylglutaryl CoA reductase (HMGR), farnesyl diphosphate synthase (FPPS) andα-farnesene synthase are the rate-limiting enzymes in the mevalonate pathway.α-Farnesene synthase is the final, rate-limiting enzyme that converts farnesyl diphosphate (FPP) toα-farnesene in the mevalonic acid (MVA) pathway of terpene biosynthesis. Studies have been focused on the control ofα-farnesene synthesis.To elucidate the relationship betweenα-farnesene synthase expression andα-farnesene synthesis during low temperature storage, the cDNA encodiongα-farnesene synthase gene was cloned from Yali pear (Pyrus bretschneideri Rehd) fruit. Specific primers for PCR designed from AFS1 had been registered in GenBank (Genbank accession number AY182241). The results were as followed: 1 An geneα-farnesene synthase gene (PFS;GenBank accession number DQ364626) with the coding region of 1824bp in length was cloned by using RT-PCR with primers based on appleα-farnesene synthase and RNA from peel tissue.2 The deduced amino acid sequence shows high identities with otherα-farnesene synthase gene from other apple and pear varieties and low identities with crops such as cucumber, pinus and picea.3 PFS gene expression andα-farnesene synthesis delayed by Diphenylamine (DPA) but inhibited by 1-methylcycropropane (1-MCP) during storage. In control, PFS gene expression andα-farnesene reached maximal in 6th week, and then dropped during continued storage, and then could hardly be detected in pear peel treated by 1-MCP, and still increased in fruit treated by DPA in 10 week.4 The expression of PFS in pericarp andα-farnesene content were the highest, the next was in leaf, and relatively lower in stem, flower and root.5 PFS gene expression was closely correlated withα-farnesene accumulation in pear.6 1-MCP at l.0μL.L^-1 and DPA at 2.0g.L^-1 treatment gave almost no scald development, but scald occured at other concentration in different degrees.