Abstract: In this study, Pphmgr1 and Pphmgr2, two members of hmgr gene family which encodes α-farnesene metabolism rate-limiting enzyme HMGR were cloned from scald-susceptible sandy pear variety 'Cuiguan' peel, respectively. Pphmgr1 cDNA has an open reading frame of 1 827 nucleotides and encodes a polypeptide including 609 residues which relative molecular mass was 64.80 kD; while Pphmgr2 cDNA has an opening reading frame of 1 707 nucleotides and encodes a polypeptide including 569 residues which relative molecular mass was 60.21 kD. The deduced amino acid sequences were from Pphmgr1 and Pphmgr2 showed 90% and 98% homology with apple MdHMGR1 and MdHMGR2, respectively. Under high temperature shelf life condition (28~32 ℃), ethylene receptor inhibitor 1-MCP significantly decreased respiration rate and alleviated ethylene production rate. At the same time, α-farnesene and conjugated trienols contents were significantly decreased and occurring times of their peak values were postponed together. The semi-quantitative RT-PCR results showed that Pphmgr1 was constitutively expression, while expression of Pphmgr2 was inhibited by 1-MCP obviously. The results showed that under the experiment temperature conditions (28-32 ℃) 1-MCP inhibited ethylene metabolism and respiration rate so as to decrease the expression abundance of Pphmgr2, which probably directly led to the depression of α-farnesene synthetic metabolism and thus to reduce the superficial scald incidence of 'Cuiguan' pear after harvest at last.

Key words: sandy pear, superficial scald, HMGR, gene, cloning, expression, 1-MCP