Submitted to: Plant Biology
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2005
Publication Date: 7/1/2005
Citation: Gapper, N.E., Whitaker, B.D., Bai, J. 2005. Inhibition of ethylene-induced alpha-farnesene synthase gene expression in d'anjou pears with 1-mcp delays alpha-farnesene synthesis and oxidation and prevents superficial scald [abstract]. Plant Biology 2005 Meeting. p.84.
Technical Abstract: Several commercial cultivars of apple and pear fruit are prone to superficial scald, a storage disorder that appears as browning or blackening of the skin, which results from necrosis of the hypodermal cortical tissue. Tissue damage is thought to be induced or exacerbated by conjugated trienol (CT) oxidation products of the sesquiterpene alpha-farnesene, which accumulate in the fruit skin during cold storage. In apple fruit, ethylene is known to play a key role in development of scald. Pre-storage treatment with 1-methylcyclopropene (1-MCP), a blocker of ethylene perception, inhibits alpha-farnesene production and CT accumulation, and largely prevents scald development after 4-6 months of storage at 0-1 C. A marked increase in expression of AFS1, the gene encoding alpha-farnesene synthase (AFS), precedes the rapid accumulation of alpha-farnesene in cold-stored apples, and 1-MCP treatment blocks the up-regulation of AFS1 gene expression. AFS converts farnesyl diphosphate to alpha-farnesene, the last step in synthesis of this sesquiterpene via the mevalonic acid pathway, and AFS1 appears to be the only gene in the pathway that is up-regulated by ethylene in the first weeks of storage. The present study was conducted to determine if the same mechanism governs alpha-farnesene production in scald-susceptible d’Anjou pear. A gene encoding AFS (PcAFS1) was cloned using RT-PCR with primers based on apple AFS1 and RNA from peel tissue of pears stored for 4-8 weeks. Control and 1-MCP-treated (0.3 ppm; 24 h) pears were stored for up to 6 months at –1 C in air. An increase in PcAFS1 expression occurred in control fruit over the first 3 months, but was greatly attenuated in 1-MCP-treated fruit. Alpha-farnesene and CTs in peel tissue extracts were quantified by HPLC-UV and scald incidence was scored at one-month intervals. Maximum levels of alpha-farnesene and CTs in control fruit occurred at 3 and 4 months, respectively, and scald incidence was 100% after 3 months. Alpha-farnesene and CT levels at these time points were, respectively, 9- and 19-fold lower in 1-MCP-treated fruit, which had no scald.